GuruPrakashAcadmy

2012-11-08T06:51:00.000-08:00

Crystal Field Theory (CFT).

2011-10-19T07:12:00.000-07:00

Crystal Field Theory (CFT), An Introduction.

Lecture 3. CHEM1902 (C 10K) Coordination Chemistry

In the ionic CFT, it is assumed that the ions are simple point charges. When applied to alkali metal ions containing a symmetric sphere of charge, calculations of energies are generally quite successful. The approach taken uses classical potential energy equations that take into account the attractive and repulsive interactions between charged particles (that is, Coulomb's Law interactions).

Electrostatic Potential is proportional to q₁ * q₂/r

where q₁ and q₂ are the charges of the interacting ions and r is the distance separating them. This leads to the correct prediction that large cations of low charge, such as K⁺ and Na⁺, should form few coordination compounds.

For transition metal cations that contain varying numbers of d electrons in orbitals that are NOT spherically symmetric, however, the situation is quite different. The shape and occupation of these d-orbitals then becomes important in an accurate description of the bond energy and properties of the transition metal compound.

To be able to understand and use CFT then, it is essential to have a clear picture of the shapes (angular dependence functions) of the d-orbitals.

Jmol is an Open Source application for the display of molecular graphics that is capable of displaying atomic orbitals so it is possible to see the relationship between their orientation and ligands in different stereochemistries. See the cases for octahedral, tetrahedral and square planar complexes.

A cube provides a convenient reference for displaying the coordination centre of complexes since octahedral compounds have cubic symmetry i.e. the six anions sit at the centres of the faces of the cube and for tetrahedral complexes the 4 ligands sit at opposite diagonal edges.

You should be able to see that two of the d-orbitals, the dz² and dx²-y² meet the faces of the cube, but the remaining three (dxy, dyz and dxz) point towards the edges of the cube and actually have a node meeting the centres of the faces.

What happens then to the energy of the d-electrons if negatively charged ligands are brought in towards the metal centre to give an octahedral complex - where the ligands sit at the centre of the faces of the cube i.e. on the X, Y and Z axes? Since the d electrons are themselves negatively charged they would experience repulsion and their energies would be raised. For 's' and 'p' electrons this is of little consequence but for 'd' electrons there will be an energy difference involved depending on the orbital distribution and occupation.

Consider the simple example of TiCl₆^3- in which six chloride ions octahedrally surround the Ti³⁺ cation. There is only one d-electron to be allocated to one of the five d- orbitals. If it were to occupy the dz² or dx²-y² orbital, both of which meet the face of the cube and thus point directly towards the chloride ligands, it would be strongly repelled. The geometry of these orbitals and their nodes would require the electron to stay near the negatively charged ligands causing even more repulsion than a spherically distributed electron would experience. On the other hand, if the electron were to occupy the dxy, dyz or dxz orbital, it would spend less time near the ligands than would a spherically distributed electron and would be repelled less.

This difference between for example the dx²-y² orbital, the dxy orbital and a spherical distribution can be graphically represented by

The result of these differences for the d-orbitals is an energy difference between the dz² and dx²-y² orbitals compared to the dxy, dyz and dxz orbitals.

The CFT approach can be easily extended to other geometries and the next most important case is the tetrahedron. To predict the splitting pattern of the energy of the d-orbitals under a tetrahedal crystal field you may once again find it convenient to consider how the ligands can fit into a cube to give a tetrahedron.

The next step is to consider how the d-orbitals interact with these incoming ligands. For tetrahedral complexes, the energy of those orbitals which point towards the edges should now be raised higher than those which point towards the faces. That is, the exact opposite of the situation we just dealt with for the octahedral crystal field. The end result is a splitting pattern which is represented in the splitting diagram above.

The square planar case can be considered as an extension of the octahedral, where we remove the two ligands from the Z axis. Consequently, repulsion of an electron in the dz² orbital will no longer be equivalent to that experienced by an electron in the dx²-y² orbital, and the end result is shown above. For the first year course, the only square planar complexes will be for d⁸ complexes, i.e all four coordinate complexes are tetrahedral except for d⁸ which may be tetrahedral or square planar.

Once we accept that the energy of the 5 'd' orbitals are no longer degenerate in a coordination compound we can begin to explore some of the implications. Note that a different CFT energy splitting diagram has to be applied for each stereochemistry. In this course we will only be concerned with diagrams for octahedral, tetrahedral and square planar complexes.

One of the important aspects of CFT is that not all ligands are identical when it comes to causing a separation of the energy of the d-orbitals. For transition metal compounds, there is clear evidence for this from the multitude of colours available for a given metal ion when the ligands or stereochemistry are varied. For octahedral complexes this is a reflection of the energy difference between the higher dz², dx²-y² (eg subset) and the dxy, dyz, dxz (t2g subset).

It has been established that the ability of ligands to cause a large splitting of the energy between the orbitals is essentially independent of the metal ion and theSPECTROCHEMICAL SERIES is a list of ligands ranked in order of their ability to cause large orbital separations.

A shortened list includes:

I- < Br- < SCN- ~Cl- < F- < OH- ~ ONO- < C₂O₄^2- < H₂O
< NCS- < EDTA^4- < NH₃ ~ pyr ~ en < bipy < phen < CN- ~ CO

When metal ions that have between 4 and 7 electrons in the d orbitals form octahedral compounds, two possible electron distributions can occur. These are referred to as either weak field - strong field or high spin - low spin configurations.

Take for example, Fe²⁺- d⁶.

The diagram on the left represents the case for the aqua ion (small Δ) and on the right that of the hexacyano ion (large Δ).

What this means is that if we use a technique that can detect the presence of unpaired electrons in each compound, then for the first we should find 4, while in the latter none. This accounts for the names high spin compared to low spin. The terms weak field, strong field give an indication of the splitting abilities of the ligand. Water always give rise to small splittings of the enregy of the d orbitals for first row transition metal ions and hence is referred to as a weak field ligand. Conversely, CN- is a strong field ligand, since it causes large splittings of the energy of the d-orbitals.

A simple JAVA applet that shows the electronic configuration for octahedral and tetrahedral complexes and calculates the spin-only magnetic moment is available.

One method of determining the number of unpaired electrons is by looking at the magnetic properties of the compounds. A simple technique to determine a magnetic moment (the GOUY METHOD) involves weighing the sample in the presence and absence of a strong magnetic field. By careful calibration using a known standard, such as Hg[Co(SCN)₄] the number of unpaired electrons can be determined.

To predict the magnetic moment, we can use the simple spin-only formula:

      μ     =   √[4S(S+l)]       Bohr Magneton    (BM)

where S is the spin quantum number (1/2 for each unpaired electron).
An alternative representation is:

      μ     =   √[n(n+2)]        Bohr Magneton    (BM)

where n is the number of unpaired electrons.
These simple formulae give good results for most first row transition metal compounds and can be refined to include orbital contributions (COVERED IN MORE DETAIL IN CHEM2101 (C21J)).

It is expected that all students will be able to calculate the spin-only magnetic moment of any coordination compound. To do this, you must know the number of d-electrons in the central metal ion, the stereochemistry and whether weak field-strong field considerations are necessary.

	K₃[Fe(oxalate)₃] 3H₂O	K₂[CuCl₄]
metal ion	Fe³⁺	Cu²⁺
number of d electrons	5	9
stereochemistry	octahedral	tetrahedral
High Spin/Low Spin	High Spin	Not relevant
# of unpaired electrons	5	1
magnetic moment	√(35) B.M	√(3) B.M

Note that if there are 1-3 or 8-9 d electrons in an octahedral complex, the spin-only magnetic moment will have the same value irrespective of whether the ligands present are considered weak field or strong field. For octahedral Co(III) complexes, we will make the simplification that all are low-spin, so regardless of the types of ligands present the magnetic moment will be μ=0, that is, diamagnetic.

The Peptide Bond - Peptide Guide

2011-10-16T22:31:00.000-07:00

The Peptide Bond

A peptide bond (sometimes mistakenly called amino bond) is a covalent bond that is formed between two molecules when the carboxyl group of one molecule reacts with the amino group of the another molecule, releasing a molecule of water. This is a a condensation reaction and usually occurs between amino acids. The resulting CO-NH bond is called a peptide bond, and the resulting molecule is an amide.

Formation of the peptide bond

The molecules must be orientated so that the carboxylic acid group of one can react with the amine group of the other. For example, two amino acids combining through the formation of a peptide bond to form a dipeptide.

Any number of amino acids can be joined together in chains of 50 amino acids called peptides, 50-100 amino acids called polypeptides, and over 100 amino acids called proteins. A number of hormones, antibiotics, antitumor agents and neurotransmitters are peptides (proteins).

A peptide bond can be broken down by hydrolysis (the adding of water). The peptide bonds that are formed within proteins have a tendency to break spontaneously when subjected to the presence of water (metastable bonds) releasing about 10 kJ/mol of free energy. This process, however, is very slow. Living organisms use enzymes to broken down or to form peptide bonds. The wavelength of absorbance for a peptide bond is 190-230 nm.

Structure of the Peptide Bond

X-ray diffraction studies of crystals of small peptides by Linus Pauling and R. B. Corey indicated that the peptide bond is rigid, and planer. Pauling pointed out that this is largely a consequence of the resonance interaction of the amide, or the ability of the amide nitrogen to delocalize its lone pair of electrons onto the carbonyl oxygen.

Because of this resonance, the C=O bond is actually longer than normal carbonyl bonds, and the N–C bond of the peptide bond is shorter than the N–Cα bond. Notice that the carbonyl oxygen and amide hydrogen are in a trans configuration, as opposed to a cis configuration. This configuration is energetically more favorable because of possible steric interactions in the other.

The Polarity of the Peptide Bond

The peptide bond is usually portrayed as a single bond between the carbonyl carbon and the amide nitrogen. Normally, this should allow free rotation about than bond. However, notice that the nitrogen has a lone pair of electrons, which are adjacent to a carbon-oxygen bond. Therefore, a reasonable resonance structure can be draw with a double bond linking the carbon and nitrogen, and which result in a negative charge on the oxygen and a positive charge on the nitrogen.

The resonance structure prevents rotation around the peptide bond. The real structure of course is a weighted hybrid of these two structures. Therefore, the question is how significant is the resonance structure in depicting the true electron distribution. It is know that the peptide bond has approximately 40% double-bond character and therefore it is rigid.

Charges give the peptide bond a permanent dipole. Because of the resonance, the oxygen has a -0.28 charge, while the nitrogen bears a +0.28 charge.

The Peptide Bond - Peptide Guide

2011-10-16T22:24:00.000-07:00

The Peptide Bond - Peptide Guide

EklavyaJEE06

2011-10-06T17:31:00.000-07:00

EklavyaJEE06: "IIT exam panel behind poor student quality: Super 30 founder

IANS | Oct. 05, 2011

PATNA: Anand Kumar, who founded Super 30, Bihar's widely acclaimed free coaching centre for Indian Institute of Technology (IIT) aspirants, has blamed the institutes' entrance exam panel for the poor quality of students making the cut, a concern voiced by Infosys chairman emeritus NR Narayana Murthy.

Anand Kumar said if poor quality students, as felt by Narayan Murthy, were able to get into the IITs, it was the responsibility of"

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EklavyaJEE06

2011-10-06T17:29:00.002-07:00

EklavyaJEE06: "Times of India :: 22 July 2011

CBI indicts IIT-Kgp chief in technical institutes scam

Akshay Mukul, TNN | July 22, 2011

NEW DELHI: Widening its net in the All India Council for Technical Education (AICTE) scam, the CBI has found the involvement of its former chairperson Damodar Acharya, who is now the director of IIT-Kharagpur.

In an investigation report sent to the HRD ministry in May, the agency also found involvement of five others in different cases of illegal approval to technical institutes. The CBI has named R A Yadav, former chairman, AICTE; Y Venkateswara Rao, director, National Institute of Technology, Warangal; M S Palanichamy, former vice-chancellor, Tamil Nadu Open University; M Afshar Alam, faculty of management and information technology, Jamia Hamdard University and M Altaf Khan of department of commerce and business studies, Jamia Millia Islamia. CB"

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EklavyaJEE06

2011-10-06T17:29:00.001-07:00

EklavyaJEE06: "tatesman Editorial :: 12 August 2011

The illegality within IIT

THE formality of the transfer of a case from a state government to the CBI is of relatively lesser moment than the astonishing fact of a campus within a campus. A fake institute styled the Institution of Electrical Engineering (IEE) was being run for quite a while within the holy of holies ~ the Indian Institute of Technology, Kharagpur. It was ostensibly engaged in the award of diplomas; neither the institution, not to mention the diplomas, were recognised by the All India Council for Technical Education. It is difficult to believe that the ITT authorities were not privy to this illegality. Yet it remained for the duped students to spill the beans and complain to the Central Vigilance Commission that it was being run by certain members of the faculty and IIT officials."

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EklavyaJEE06

2011-10-06T17:29:00.000-07:00

EklavyaJEE06: "Telegraph :: 11 August 2011

CBI waits for Bengal nod on IIT case

BASANT KUMAR MOHANTY

New Delhi, Aug. 10: The CBI has refused to take up the probe into a fake institute that was being run on the IIT Kharagpur campus on the ground that the Bengal government has to first transfer the case that state police are now investigating.

“The state police will have to agree to transfer the case to the CBI. We have asked the state government to expedite the process of investigation by the state police or agree to transfer the c"

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EklavyaJEE06

2011-10-06T17:28:00.000-07:00

EklavyaJEE06: "Telegraph :: 22 August 2011

Graft glare on IIT Bbsr director scam

BASANT KUMAR MOHANTY

New Delhi, Aug. 21: The HRD ministry is likely to frame charges against IIT Bhubaneswar director Madhusudan Chakraborty for alleged involvement in irregularities related to equipment purchases worth Rs 2.5 crore last year.

The charges could be framed this month by the ministry’s vigilance wing on the basis of the lapses detected by the CBI in the purchases."

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EklavyaJEE06

2011-10-06T17:27:00.000-07:00

EklavyaJEE06: "Rot starts at top: Indicted IIT chiefs go scot-free

Akshay Mukul, TNN | Oct. 05, 2011

NEW DELHI: Poor quality of engineers is not the only problem afflicting the IITs. The rot has set in from the top. At least two of its directors - Damodar Acharya of IIT-Kharagpur and A K Bhowmick of IIT-Patna - are still in office, despite the Central Bureau of Investigation's indictment in the past.

The HRD ministry appointed Bhowmick as dire"

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Oshodhara | Osho's Biography - Part V (1957-1970 Teaching and Travelling)

2011-09-22T22:44:00.000-07:00

Oshodhara | Osho's Biography - Part V (1957-1970 Teaching and Travelling): "ometimes I would go to the library or just chitchat with the professors and come back again. There was nothing else for me to do. person18
Osho writes to a friend:
Sanskrit Mahavidyalaya
Raipur
23 September 1957
Respected Deria ji,
I have come here the day before yesterday. I have been appointed by the State government in Sanskrit Mahavidyalaya (College), Raipur. I had joined the college the day before yesterday itself: the heart was very sad at the time of signing in: a feeling persisted as if the moments of freedom are coming to an end. Teaching in a college feels to be very dead: it does not impart any message of life. In the heart of my heart I know that I am not for all this, but one will have to wait for that moment and the day when one will be able to engage in that work which will truly make my 'I' my 'I'. That day I will become a dwija, the twice-born: I will be born again. 'I' will be truly born. I am incessantly praying for that day.
How is Satya? My love to all. By 5th or 6th October I am reaching home. The rest is all fine. My respects to honourable Lal Saheb and others. What are you doing: write.
Rajneesh Ke Pranam letter04

"

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Oshodhara | Osho's Biography - Part IV (1951-1957 University Student )

2011-09-22T22:18:00.000-07:00

Oshodhara | Osho's Biography - Part IV (1951-1957 University Student ): "I stood outside their house with my small suitcase, and told my father's sister that, "Your husband is unwilling to have me here, and unless he is willing it would be better for me to live on the street than to be in his house. I cannot enter unless I am convinced that he will be happy to have me. And I cannot promise that I will not be a trouble to you. It is against my nature to not be in trouble. I am just helpless."
The husband was hidden behind a curtain, listening to everything. He understood one thing at least, that the boy was worth trying.
He came out and said, "I will give you a try."
I said, "Rather you learn from the very beginning that I am giving you a try."
He said, "What!""

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Chromyl chloride - Wikipedia, the free encyclopedia

2011-09-22T21:55:00.000-07:00

Chromyl chloride - Wikipedia, the free encyclopedia: "Chromyl chloride is a chemical compound with the formula CrO2Cl2. This compound is an opaque dark blood-red liquid at room temperature and pressure. It is tetrahedral, somewhat like SO2Cl2. CrO2Cl2 is similar to the most commonly encountered chromium(VI) derivative chromate, [CrO4]2−; both are tetrahedral Cr(VI) compounds. However, they differ in both oxidizing power and in physical properties: one is a liquid and the other forms salts.
CrO2Cl2 is a neutral molecular species. This means that in the liquid and solid forms, the individual CrO2Cl2 entities interact purely via van der Waals bonding. Such weak bonding leads to low melting and boiling points, which is related to the fact that it is a distillable liquid.
The diminished oxidizing power of [CrO4]2− vs. CrO2Cl2 can be ascribed to its anionic nature, which diminishes its electron affinity. Also, chloride is a poorer pi-donor ligand than is oxide."

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Oshodhara | Osho's Biography - Part V (1957-1970 Teaching and Travelling)

2011-09-22T21:42:00.000-07:00

Oshodhara | Osho's Biography - Part V (1957-1970 Teaching and Travelling): "Ch 45: First Talk in English to Westerners

The first occasion Osho speaks publicly in English to a Western audience is in September 1969 at Pahalgam in Kashmir, where followers of Maharishi Mahesh Yogi invite Osho to talk to them. Maharishi teaches 'Transcendental Meditation', a 20-minute repetition of a mantra.
When I started using English, for two or three months I was thinking in Hindi and speaking in English. It was a double trouble. last413
I don't know English but I manage. I am surprised myself because English is such an unscientific language and I am not acquainted with it in any way, but when you have to say something, when you have something to say, then the language follows. If you have just a little bit of an acquaintance with the words they follow, they fall in line. dark14
I don't care. What does it matter if a word here and there is mispronounced? My whole life I have been mispronouncing. books07
I have met Maharishi Mahesh Yogi just by accident. I was having a camp in Pahalgam in Kashmir and he was also having a camp in "

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Osho Rajneesh

2011-09-22T21:35:00.000-07:00

Osho Rajneesh:

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Aluminium >> Extraction

2011-09-22T19:53:00.001-07:00

Aluminium >> Extraction: "The first step in extracting aluminium is to remove it from the Earth in mining. This is relatively simple given the abundance of the material. However aluminium is never found isolated in the Earth (due to its reactivity) but instead it is found bound to other elements in compounds. This means that aluminium alone in can never be dug up, but compounds of it, often containing oxygen and silicon, are."

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Calcium Oxide (CaO) Lime

2011-09-21T19:35:00.001-07:00

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Calcium oxide is commonly called Quick Lime. Quick lime has always been a cheap commodity because limestone deposits are readily available. Lime manufacturing and application dates back to the Roman, Greek and Egyptian civilizations.
Sub Topics
Raw Materials
Calcium carbonate and magnesium carbonate obtained from deposits of limestone, chalk, marble, dolomite, oyster shells, stalactites and stalagmites. Vertical or horizontal kilns are used to burn limestone. The kilns have steel shells line with refracting bricks.

Calcium oxide or lime is prepared by the calcination process. Limestone or calcium carbonate is heated to a temperature between 1200oC and 1300oC in Kilns and it decomposes to quicklime and carbon dioxide.

A Vertical Lime Kiln

This is a reversible reaction. It is exothermic in the forward direction. To ensure that the limestone is completely converted to lime, carbon dioxide is allowed to escape from the Kiln. This makes carbon dioxide unavailable for the reverse reaction.

Properties of Quick LimeBack to Top

Lime is a white amorphous solid.
It has a high melting point of 2600oC.
It is highly stable and even fusion cannot decompose it.

Chemical Properties
On hydration, quick lime forms slaked lime or lime water. When water is added to lime it becomes hot and cracks to form a white powder. This is called slaking of lime.
Calcium oxide is a basic oxide. It can react with acids to give calcium salts.
With acidic oxides like silicon dioxide and phosphorus pentoxide, it forms silicates and phosphates. This property makes lime useful as a flux in metallurgy to remove impurities.

Uses of LimeBack to Top

Lime is indispensable for use with mortar and plaster.
Lime is used for medicinal purposes, insecticides and plant and animal food.
It is used as a laboratory reagent for gas absorption, precipitation, dehydration etc.
It is used as a reagent in the manufacture of paper, high grade steel and cement.
If finds use in dehairing hides.
It can be used for water softening and in the recovery of ammonia (by-product of Solvay process).
It finds enormous use in the manufacture of soap, rubber, varnish, refractories and lime bricks.
It also finds use in the preparation of calcium carbide, basic calcium nitrate and calcium bisulphite.
Improves the quality of soil.

PROPERTIES OF THE PERIOD 3 "HYDROXIDES"

2011-09-20T05:55:00.001-07:00

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This page looks briefly at how the chemistry of the "hydroxides" of the Period 3 elements from sodium to chlorine varies as you cross the period.

I am taking the word "hydroxide" to include anything which contains either a hydroxide ion or an -OH group covalently bound to the element in question. You wouldn't usually think of some of the compounds on this page as hydroxides at all. A quick summary of the trendsSodium and magnesium hydroxides These contain hydroxide ions, and are simple basic hydroxides. Aluminium hydroxide Aluminium hydroxide, like aluminium oxide, is amphoteric - it has both basic and acidic properties.
	Note: I have no real idea of how to describe aluminium hydroxide on the ionic-covalent spectrum. Part of the problem is that there are several forms of aluminium hydroxide. For example, when it is prepared by adding ammonia solution to a solution containing hexaaquaaluminium ions, [Al(H₂O)₆]³⁺, it is probably first formed as the covalently bound Al(H₂O)₃(OH)₃. But this will lose water and rearrange itself on standing - and I don't know what exactly is formed.The chemistry textbooks that I have to hand aren't too clear about the structure of aluminium hydroxide as far as the degree of covalent character is concerened, and a web search (until I got totally bored with it!) didn't throw up any reliable chemistry sites which discussed it. Several geology sites describe the mineral gibbsite (a naturally occurring form of aluminium hydroxide) in terms of ions, but whether it actually contains ions or whether this is just a simplification as a convenient way of talking about and drawing a complicated structure, I don't know.
The other "hydroxides" In all of these have -OH groups covalently bound to the atom from period 3. These compounds are all acidic - ranging from the very weakly acidic silicic acids (one of which is shown below) to the very strong sulphuric or chloric(VII) acids. There are other acids (also containing -OH groups) formed by these elements, but these are the ones where the Period 3 element is in its highest oxidation state. Adding some detailSodium and magnesium hydroxides These are both basic because they contain hydroxide ions - a strong base. Both react with acids to form salts. For example, with dilute hydrochloric acid, you get colourless solutions of sodium chloride or magnesium chloride. Aluminium hydroxide Aluminium hydroxide is amphoteric. Like sodium or magnesium hydroxides, it will react with acids. This is showing the basic side of its nature. With dilute hydrochloric acid, a colourless solution of aluminium chloride is formed. But aluminium hydroxide also has an acidic side to its nature. It will react with sodium hydroxide solution to give a colourless solution of sodium tetrahydroxoaluminate.
	Note: You may find all sorts of other formulae given for the product from this reaction. These range from NaAlO₂ (which is a dehydrated form of the one in the equation) to Na₃Al(OH)₆ (which is a different product altogether). What you actually get will depend on things like the temperature and the concentration of the sodium hydroxide solution. In any case, the truth is almost certainly a lot more complicated than any of these. (That's equally true of the previous equation involving the acid.) This is a case where it is a good idea to find out what your examiners quote in their support material or mark schemes, and stick with that.If necessary, get this sort of information from your Exam Board by following the links on the syllabuses page.
The other "hydroxides" A quick reminder of what we are talking about here: None of these contains hydroxide ions. In each case the -OH group is covalently bound to the Period 3 element, and in each case it is possible for the hydrogens on these -OH groups to be removed by a base. In other words, all of these compounds are acidic. But they vary considerably in strength: Orthosilicic acid is very weak indeed. Phosphoric(V) acid is a weak acid - although somewhat stronger than simple organic acids like ethanoic acid. Sulphuric acid and chloric(VII) acids are both very strong acids. The main factor in determining the strength of the acid is how stable the anion (the negative ion) is once the hydrogen has been removed. This in turn depends on how much the negative charge can be spread around the rest of the ion. If the negative charge stays entirely on the oxygen atom left behind from the -OH group, it will be very attractive to hydrogen ions. The lost hydrogen ion will be easily recaptured and the acid will be weak. On the other hand, if the charge can be spread out (delocalised) over the whole of the ion, it will be so "dilute" that it won't attract the hydrogen back very easily. The acid will then be strong. Wherever possible, the negative charge is delocalised by interacting with doubly-bonded oxygens. For example, in chloric(VII) acid, the ion produced is the chlorate(VII) ion (also known as the perchlorate ion), ClO₄^-. The structure of the ion doesn't stay like this: Instead, the negative charge is delocalised over the whole ion, and all four chlorine-oxygen bonds are identical.
	Note: This is just like the delocalisation which occurs in the ethanoate ion formed when ethanoic acid is behaving as a weak acid (except on a larger scale). You will find this described in some detail on a page about organic acids.Use the BACK button on your browser if you choose to follow this link.
When sulphuric acid loses a hydrogen ion to form the hydrogensulphate ion, HSO₄^-, the charge can be spread over three oxygens (the original one with the negative charge, and the two sulphur-oxygen double bonds. That's still an effective delocalisation, and sulphuric acid is almost as strong as chloric(VII) acid.
	Note: Sulphuric acid can, of course, lose a second hydrogen ion as well from the other -OH group and form sulphate ions. However, that is a bit more difficult. If you lose that second hydrogen, you can use all four oxygens to delocalise the charge - but now you have to delocalise two negative charges rather than just one. The hydrogensulphate ion isn't a strong acid. It's strength is similar to phosphoric(V) acid.
Phosphoric(V) acid is much weaker than sulphuric acid because it only has one phosphorus-oxygen double bond which it can use to help delocalise the charge on the ion formed by losing one hydrogen ion - so the charge on that ion is delocalised less effectively. In orthosilicic acid, there aren't any silicon-oxygen double bonds to delocalise the charge. That means the ion formed by loss of a hydrogen ion isn't at all stable, and easily recovers its hydrogen.

An introduction to Lead Chemistry

2011-09-18T20:39:00.000-07:00

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Overview

Lead is the heaviest member of the carbon family. The carbon family consists of the five elements in Group 14 (IVA) of the periodic table. The periodic table is a chart that shows how chemical elements are related to each other. Although a member of the carbon family, lead looks and behaves very differently from carbon.
Lead is one of only a few elements known to ancient peoples. One of the oldest examples of lead is a small statue found in Egypt. It was made during the First Dynasty, in about 3400 B.C. Mention of lead and lead objects can also be found in very old writing from India. And the Bible mentions lead in a number of passages.

SYMBOL
Pb
ATOMIC NUMBER
82
ATOMIC MASS
207.2
FAMILY
Group 14 (IVA)
Carbon
PRONUNCIATION
LED

Throughout history, Lead has been used to make water and sewer pipes; roofing; cable coverings; type metal and other alloys; paints; wrappings for food, tobacco, and other products; and as an additive in gasoline. Since the 1960s, however, there has been a growing concern about the health effects of lead. For instance, scientists have found that lead can cause mental and physical problems in growing children. As a result, many common lead products are now being phased out.

Discovery and naming

Lead has been around for thousands of years. It is impossible to say when humans first discovered the element. It does not occur as an element in the earth very often. But one of its ores, lead sulfide (PbS), is fairly common. It is not difficult to obtain pure lead metal from lead sulfide. Humans probably discovered methods for doing so thousands of years ago.

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By Roman times, lead metal was widely used. The far-reaching system that brought water to Rome contained many lead pipes. Sheets of lead were used as writing tablets and some Roman coins were also made of lead. Perhaps of greatest interest was the use of lead in making pots and pans. Modern scientists believe many Romans may have become ill and died because of this practice. Cooking liquids in lead utensils tends to make the lead dissolve. It got into the food being cooked. People who ate those foods got more and more lead into their bodies. Eventually, the effects of lead poisoning must have begun to appear.
Of course, the Romans had little understanding of the connection between lead and disease. They probably never realized that they were poisoning themselves by using lead pots and pans.
No one is quite sure how lead got its name. The word has been traced to manuscripts that date to before the 12th century. Romans called the metal plumbum. It is from this name that the element's chemical symbol comes: Pb. Compounds of lead are sometimes called by this old name, such as plumbous chloride.

Physical properties

Lead is a heavy, soft, gray solid. It is both ductile and malleable. Ductile means capable of being drawn into thin wires. Malleable means capable of being hammered into thin sheets. It has a shiny surface when first cut, but it slowly tarnishes (rusts) and becomes dull. Lead is easily worked. "Working" a metal means bending, cutting, shaping, pulling, and otherwise changing the shape of the metal.
The melting point of lead is 327.4°C (621.3°F), and its boiling point is 1,750 to 1,755°C (3,180 to 3,190°F). Its density is 11.34 grams per cubic centimeter. Lead does not conduct an electric current, sound, or vibrations very well.

Chemical properties

Lead is a moderately active metal. It dissolves slowly in water and in most cold acids. It reacts more rapidly with hot acids. It does not react with oxygen in the air readily and does not burn.

Occurrence in nature

The abundance of lead in the Earth's crust is estimated to be between 13 and 20 parts per million. It ranks in the upper third among the elements in terms of its abundance.
Lead rarely occurs as a pure element in the earth. Its most common ore is galena, or lead sulfide (PbS). Other ores of Lead are anglesite, or lead sulfate (PbSO ₄); cerussite, or lead carbonate (PbCO ₃); and mimetite (PbCL ₂○ Pb ₃(AsO ₄) ₂).
The largest producers of lead ore in the world are Australia, China, the United States, Peru, Canada, Mexico, and Sweden. In the United States, more than 93 percent of all the lead produced comes from Missouri. Other lead-producing states are Montana, Colorado, Idaho, Illinois, New York, and Tennessee. In 1996, 426,000 metric tons of lead were produced in the United States.

Isotopes

Four naturally occurring isotopes of lead occur. They are lead-204, lead-206, lead-207, and lead-208. Isotopes are two or more forms of an element. Isotopes differ from each other according to their mass number. The number written to the right of the element's name is the mass number. The mass number represents the number of protons plus neutrons in the nucleus of an atom of the element. The number of protons determines the element, but the number of neutrons in the atom of any one element can vary. Each variation is an isotope.
About sixteen radioactive isotopes of lead are known also. A radioactive isotope is one that breaks apart and gives off some form of radiation. Radioactive isotopes are produced when very small particles are fired at atoms. These particles stick in the atoms and make them radioactive.

Romans routinely ate food cooked in lead pots and pans. The connection between lead and disease was not known then, so many people became ill and died of lead poisoning.

One radioactive isotope of lead, lead-210, is sometimes used in medicine. This isotope gives off radiation that can kill cancer cells. It is also used to treat non-cancerous eye disorders.

Lead smelting.

Extraction

Lead is obtained from its ores by a method used with many metals. First, the ore is roasted (heated in air). Roasting, also called smelting, converts the ore to a compound of lead and oxygen, lead oxide (PbO ₂). Lead oxide is then heated with charcoal (pure carbon). The carbon takes oxygen away from the lead oxide. It leaves pure lead behind:
Lead obtained in this way is not very pure. It can be purified electrolytically. Electrolytic refining involves passing an electric current through a compound. Very pure lead is collected at one side of the container in which the reaction is carried out.

A major source of lead is recycled car batteries.

Lead is also recovered in recycling programs. Recycling is the process by which a material is retrieved from a product that is no longer used. For example, old car batteries were once just thrown away. Now they are sent to recycling plants where lead can be extracted and used over and over again. It is not necessary to get all the lead that industry needs from new sources, such as ores.

Uses

The lead industry is undergoing dramatic change. Many products once made with lead no longer use the element. The purpose of this change is to reduce the amount of lead that gets into the environment. Examples of such products include ammunition, such as shot and bullets; sheet lead used in building construction; solder; water and sewer pipes; ball bearings; radiation shielding; and gasoline. These changes are possible because manufacturers are finding safer elements to use in place of lead.

The price of a gallon of gas

F or many years, lead was regarded as a miracle chemical by the automotive industry. The power to run a car comes from the burning of gasoline in the engine. However, burning gasoline is not a simple process. Many things happen inside an engine when gasoline burns in the carburetor.
For example, an engine can "knock" if the gasoline does not burn properly. "Knocking" is a "bang-bang" sound from the engine. It occurs when low-grade gasoline is used.
One way to prevent knocking is to use high-grade gasoline. Another way is to add chemicals to the gasoline. The best gasoline additive discovered was a compound called tetraethyl lead (Pb(C ₂H ₅) ₄). Tetraethyl lead was usually called "lead" by the automotive industry, the consumer, and advertisers. When someone bought "leaded" gasoline, it contained not lead metal, but tetraethyl lead.
Leaded gasoline was a great discovery. It could be made fairly cheaply and it prevented car engines from knocking. No wonder people thought it was a miracle chemical.
What people didn't realize was that tetraethyl lead breaks down in a car engine because of the high temperature at which engines operate. When tetraethyl lead breaks down, elemental lead (Pb) is formed:
The result—with millions of cars being driven every day—was more and more lead getting into the air. And more and more people inhaled that lead. Eventually, doctors began to see more people with leadrelated diseases.
The federal government finally decided that tetraethyl lead was too dangerous to use in gasoline. By 1990, the use of this compound had been banned by all governments in North America.

Other uses of lead have not declined. The best example is lead storage batteries. A lead storage battery is a device for converting chemical energy into electrical energy. Almost every car and truck has at least one lead storage battery. But no satisfactory substitute for it has been found. About 87 percent of all lead produced in the United States now goes to the manufacture of lead storage batteries. In addition to cars and trucks, these batteries are used for communication networks and emergency power supplies in hospitals, and in forklifts, airline ground equipment, and mining vehicles.

Compounds

A small percentage of lead is used to make lead compounds. Although the amount of lead is small, the variety of uses for these compounds is large. Some examples of important lead compounds are:

lead acetate (Pb(C ₂H ₃O ₂) ₂): insecticides; waterproofing; varnishes; dyeing of cloth; production of gold; hair dye
lead antimonate (Pb ₃(SbO ₄) ₂): staining of glass, porcelain and other ceramics
lead azide (Pb(N ₃) ₂): used as a "primer" for high explosives
lead chromate ("chrome yellow"; PbCrO ₄): industrial paints (use restricted by law)
lead fluoride (PbF ₂): used to make lasers; specialized optical glasses
lead iodide (PbI ₂): photography; cloud seeding to produce rain
lead naphthenate (Pb(C ₇H ₁₂O ₂)): wood preservative; insecticide; additive for lubricating oil; paint and varnish drier
lead phosphite (2PbO ○ PbHPO ₃): used to screen out ultraviolet radiation in plastics and paints
lead stearate (Pb(C ₁₈H ₃₅O ₂) ₂): used to make soaps, greases, waxes, and paints; lubricant; drier for paints and varnishes
lead telluride (PbTe): used to make semiconductors, photoconductors, and other electronic equipment

Health effects

The health effects of lead have become much better understood since the middle of the 20th century. At one time, the metal was regarded as quite safe to use for most applications. Now lead is known to cause both immediate and long-term health problems, especially with children. It is toxic when swallowed, eaten, or inhaled.
Young children are most at risk from lead poisoning. Some children have a condition known as pica. They have an abnormal desire to eat materials like dirt, paper, and chalk. Children with pica sometimes eat paint chips off walls. At one time, many interior house paints were made with lead compounds. Thus, crawling babies or children with pica ran the risk of eating large amounts of lead and being poisoned.
Some symptoms of lead poisoning include nausea, vomiting, extreme tiredness, high blood pressure, and convulsions (spasms). Over a long period of time, these children often suffer brain damage. They lose the ability to carry out normal mental functions.
Other forms of lead poisoning can also occur. For example, people who work in factories where lead is used can inhale lead fumes. The amount of fumes inhaled at any one time may be small. But over months or years, the lead in a person's body can build up. This kind of lead poisoning can lead to nerve damage and problems with the gastrointestinal system (stomach and intestines).

Lead causes both immediate and longterm health problems, especially with children. It is toxic when swallowed, eaten, or inhaled.

Today, there is an effort to reduce the use of lead in consumer products. For instance, older homes are often tested for lead paint before they are resold. Lead paint has also been removed from older school buildings.

An Introduction to Sulfur

2011-09-18T19:48:00.000-07:00

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Overview

Sulfur belongs to the chalcogen family. Other members of the family are oxygen, selenium, tellurium, and polonium. These elements make up Group 16 (VIA) of the periodic table. The periodic table is a chart that shows how chemical elements are related to each other.

The term chalcogen comes from two Greek words meaning "ore forming." An ore is a naturally occurring mineral used as a source for an element. Many ores are compounds of a metal and oxygen or a metal and sulfur. Compounds that contain two elements, one of which is sulfur, are called sulfides. For example, a beautiful gold-colored mineral is called pyrite, or "fool's gold," because it looks so much like real gold. Pyrite is iron sulfide (FeS ₂).
Sulfur was known to ancient peoples. Its physical and chemical properties are very distinctive. It often occurs as a brilliant yellow powder. When it burns, it produces a clear blue flame and a very strong odor.

SYMBOL
S
ATOMIC NUMBER
16
ATOMIC MASS
32.064
FAMILY
Group 16 (VIA)
Chalcogen
PRONUNCIATION
SUL-fur

Sulfur, also spelled as sulphur, is a very important element in today's world. Its most important use is in the manufacture of sulfuric acid (H ₂SO ₄). There is more sulfuric acid made than any other chemical in the world. It has an enormous number of important uses.

Discovery and naming

Sulfur must have been well known to ancient peoples. They sometimes referred to it as brimstone. Sulfur sometimes occurs in bright yellow layers on the top of the earth. It has a sharp, offensive odor. When it burns, it gives off a strong, suffocating smell. The odor is like that produced when a match is struck.

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The Bible mentions brimstone in a number of places. For example, Sodom and Gomorrah were two towns destroyed by God for the wicked ways of their citizens: "The Lord rained upon Sodom and upon Gomorrah brimstone and fire."
But ancient people certainly did not think about sulfur the way modern chemists do. In fact, they used the word "element" to talk about anything that was basic. Ancient Greek philosophers, for example, thought that everything consisted of four elements: earth, fire, water, and air. Other philosophers thought there were only two elements: sulfur and mercury.
But early thinkers were often confused as to what they meant by the word "sulfur." They often were talking about anything that burned and gave off large amounts of smoke. To them, "sulfur" was really a "burning substance." It took centuries for scientists to identify sulfur as an element.

Physical properties

Sulfur exists in two allotropic forms. Allotropes are forms of an element with different physical and chemical properties. The two forms of sulfur are known as α-form and β-form (the Greek letters alpha and beta, respectively). Both allotropes are yellow, with the α-form a brighter yellow and the β-form a paler, whitish-yellow. The α-form changes to the β-form at about 94.5°C (202°F). The α-form can be melted at 112.8°C (235.0°F) if it is heated quickly. The β-form has a melting point of 119°C (246°F). The boiling point of the α-form is 444.6°C (832.3°F).
The two allotropes have densities of 2.06 grams per cubic centimeter (α-form) and 1.96 grams per cubic centimeter (β-form). Neither allotrope will dissolve in water. Both are soluble

Solid sulfur.

in other Liquids, such as benzene (C ₆H ₆), carbon tetrachloride (CCl ₄), and carbon disulfide (CS ₂).
Another allotrope of sulfur is formed when the element is melted. This allotrope has no crystalline shape. It looks like a dark brown, thick, melted plastic.

Chemical properties

Sulfur's most prominent chemical property is that it burns. When it does so, it gives off a pale blue flame and sulfur dioxide (SO ₂) gas. Sulfur dioxide has a very obvious strong, choking odor.

Sulfur sometimes occurs in bright yellow layers on the top of the earth. It has a sharp, offensive odor.

Sulfur also combines with most other elements. Sometimes it combines with them easily at room temperature. In other cases, it must be heated. The reaction between magnesium and sulfur is typical. When the two elements are heated, they combine to form magnesium sulfide (MgS):

A chemical reaction involving sulfur.

Sulfur also combines with hydrogen gas:
The compound formed in this reaction is hydrogen sulfide (H ₂S). Hydrogen sulfide has one of the best known odors of all compounds. It smells like rotten eggs. Hydrogen sulfide is added to natural gas (methane) used in homes for cooking and heating. Methane is odorless. So the unique smell of hydrogen sulfide makes it easy to know when there is a methane leak.

Occurrence in nature

At one time, sulfur occurred in layers along the Earth's surface. They were easy for humans to find and take. Deposits like these are more difficult to find today. One place they still occur is in the vicinity of volcanoes. Sulfur is released from volcanoes as a gas. When it reaches the cold air, it changes back to a solid. It forms beautiful yellow deposits along the edge of a volcano.
Large supplies of sulfur still occur underground. They are removed by the Frasch process (see accompanying sidebar).
Sulfur also occurs in a number of important minerals. Some examples are barite, or barium sulfate (BaSO ₄); celestite, or strontium sulfate (SrSO ₄); cinnabar, or mercury sulfide (HgS); galena, or lead sulfide (PbS); pyrites, or iron sulfide (FeS ₂); sphalerite, or zinc sulfide (ZnS); and stibnite, or antimony sulfide (Sb ₂S ₃).
The abundance of sulfur in the Earth's crust is thought to be about 0.05 percent. It ranks about number 16 among the elements in terms of their abundance in the earth. It is more abundant than carbon, but less abundant than barium or strontium.
The largest producers of sulfur in the world are the United States, Canada, China, Russia, Mexico, and Japan. In 1996, the United States produced about 11,800,000 metric tons of sulfur. It is mined in 30 states, Puerto Rico, and the U.S. Virgin Islands.

Isotopes

There are four naturally occurring isotopes of sulfur: sulfur-32, sulfur-33, sulfur-34, and sulfur-36. Isotopes are two or more forms of an element. Isotopes differ from each other according to their mass number. The number written to the right of the element's name is the mass number. The mass number represents the number of protons plus neutrons in the nucleus of an atom of the element. The number of protons determines the element, but the number of neutrons in the atom of any one element can vary. Each variation is an isotope.

Sulfur occurs in the vicinity of volcanoes.

Six radioactive isotopes of sulfur are known also. A radioactive isotope is one that breaks apart and gives off some form of radiation. Radioactive isotopes are produced when very small particles are fired at atoms. These particles stick in the atoms and make them radioactive.
One radioactive isotope of sulfur, sulfur-35, is used commercially. In medicine, the isotope is used to study the way fluids occur inside the body. It also has applications in research as a tracer. A tracer is a radioactive isotope whose presence in a system can easily be detected. The isotope is injected into the system at some point. Inside the system, the isotope gives off radiation. That radiation can be followed by means of detectors placed around the system.
As an example, a company that makes rubber tires might want to know what happens to the sulfur added to tires. Sulfur-35 is added to rubber along with non-radioactive sulfur. Researchers follow the radioactive isotope in the tires to see what happens to the sulfur when the tires are used.

The Frasch method of removing sulfur

T he Frasch method is one of the most famous mining systems ever invented. It was developed by German-American chemist Herman Frasch (1851-1914) in 1887.
The Frasch method is based on the low melting point of sulfur. The element melts at a temperature slightly higher than that of boiling water (100°C). Here is how the method works:
A set of three nested pipes (one inside each other) is sunk into the ground. The innermost pipe has a diameter of about an inch. The middle pipe has a diameter of about four inches. And the outer pipe has a diameter of about eight inches.
A stream of superheated water is injected into the outer pipe. Superheated water is water that is hotter than its boiling point, but that has not started to boil. Superheated water can be made by raising the pressure on the water. Its temperature can reach 160°C (320°F).
The superheated water passes down the outer pipe into the underground sulfur, causing it to melt. The molten (melted) sulfur forms a lake at the bottom of the pipe.
At the same time, a stream of hot air under pressure is forced down the innermost (one-inch) pipe. The hot air stirs up the molten sulfur and hot water at the bottom of the pipe. A foamy, soupy mixture of sulfur and water is formed. The mixture is forced upward through the middle pipe. When it reaches the surface, it is collected. The sulfur cools and separates from the water.

Similar applications of sulfur-35 involve studying sulfur in steel when it is made, seeing how sulfur affects the way engines operate, following what happens when proteins (which contain sulfur) are digested, and learning how drugs that contain sulfur are processed in the body.

Extraction

Like coal, sulfur sometimes occurs in thick layers under ground. One way to remove sulfur would be to mine it the way coal is mined. But a much easier method for removing sulfur from the ground is the Frasch method (see accompanying sidebar).

Uses

Sulfur has relatively few uses as an element. One of the most important of those uses is in vulcanization. Vulcanization is the process of adding sulfur to rubber to make it stiff and hard. It keeps the rubber from melting as it gets warmer. The discovery of vulcanization by Charles Goodyear (1800-60) in 1839 is one of the greatest industrial accomplishments of modern times.
Some powdered sulfur is also used as an insecticide. It can be spread on plants to kill or drive away insects that feed on the plants. By far the majority of sulfur is used, however, to make sulfur compounds. The most important of these is sulfuric acid (H ₂SO ₄).

Compounds

Nearly 90 percent of all sulfur produced goes into sulfuric acid. Sulfuric acid is the number one chemical in the world in terms of the amount produced. Each year, almost twice as much sulfuric acid is made as the next highest chemical, nitrogen. In 1996, more than 45 million tons of sulfuric acid were produced in the United States alone.
The greatest portion, nearly 75 percent, of sulfuric acid is used to make fertilizers. The next most important use, 10 percent, is in the petroleum industry. Other important uses of sulfuric acid are in the treatment of copper ores; the production of paper and paper products; the manufacture of other agricultural chemicals; and the production of plastics, synthetic rubber, and other synthetic materials.

Vulcanization is the process of adding sulfur to rubber to make it stiff and hard.

Sulfuric acid is also used in smaller amounts to make explosives, water treatment chemicals, storage batteries, pesticides,

Reaction of sulfuric acid and sugar.

drugs, synthetic fibers, and many other chemicals used in everyday life.

Health effects

The cleansing power of sulfur has been known for many centuries. At one time, ancient physicians burned sulfur in a house to cleanse it of impurities. Creams made with sulfur were used to treat infections and diseases. In fact, sulfur is still used to treat certain medical problems. Sulfur is prepared in one of three forms. Precipitated sulfur (milk of sulfur) is made by boiling sulfur with lime. Sublimed sulfur (flowers of sulfur) is pure sulfur powder. And washed sulfur is sulfur treated with ammonia water. Washed sulfur is used to kill parasites (organisms that live on other organisms) such as fleas and ticks. It is also used as a laxative, a substance that helps loosen the bowels.
Sulfur is a macronutrient for both plants and animals. A macronutrient is an element needed in relatively large amounts to insure the good health of an organism. Sulfur is used to make proteins and nucleic acids, such as DNA. It also occurs in many essential enzymes. Enzymes are chemicals that make chemical reactions occur more quickly in cells. Humans usually have no problem getting enough sulfur in their diets. Eggs and meats are especially rich in sulfur.
A person who does not get enough sulfur in his or her diet develops certain health problems. These include itchy and flaking skin and improper development of hair and nails. Under very unusual conditions, a lack of sulfur can lead to death. Such conditions would be very rare, however.

The cleansing power of sulfur has been known for many centuries.

Plants require sulfur for normal growth and development. When plants do not get enough sulfur from the soil, their young leaves start to turn yellow. Eventually, this yellowing extends to the whole plant. The plant may develop other diseases as a result.

Read more: http://www.chemistryexplained.com/elements/P-T/Sulfur.html#ixzz1YRZDWLry

An Introduction Silver

2011-09-18T19:14:00.001-07:00

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Overview

Chemists classify silver as a transition metal. The transition metals are elements between Groups 2 and 13 in the periodic table. The periodic table is a chart that shows how chemical elements are related to one another. More than 40 elements, all metals, fall within the transition metal range.
Silver is also classified as a precious metal. Precious metals are not very abundant in the Earth's crust. They are attractive and not very chemically active. These properties make the metal desirable in jewelry, coins, and art. About a half dozen metals near silver in the periodic table are also precious metals. These include gold, platinum, palladium, rhodium, and indium.
Silver has been used by humans for thousands of years. It often occurs as a free element in nature. It can also be extracted from its ores fairly easy. These properties made it easy for early humans to learn about silver.

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SYMBOL
Ag
ATOMIC NUMBER
47
ATOMIC MASS
107.868
FAMILY
Group 11 (IB)
Transition metal
PRONUNCIATION
SIL-ver

Today, the most important use of silver is in photography. Three silver compounds used in photography are silver chloride (AgCl), silver bromide (AgBr), and silver iodide (AgI). Silver is also used to make electrical equipment, mirrors, medical and dental equipment, and jewelry. It is often used to make alloys with gold for some of these applications. An alloy is made by melting and mixing two or more metals. The mixture has properties different from those of the individual metals.

Discovery and naming

Silver was probably first discovered after gold and copper. Gold and copper often occur as free elements in nature. They have very distinctive colors, which made it easy for early humans to find these metals.
Silver also occurs as a free metal, but much less often than gold or copper. At some point, humans learned to extract silver from its ores. But that discovery must have occurred very early on in human history. Archaeologists (scientists who study ancient civilizations) have found silver objects dating to about 3400 B.C. in Egypt. Drawings on some of the oldest pyramids show men working with metal, probably extracting silver from its ores.
Other early cultures also used silver. Written records from India describe the metal as far back as about 900 B.C. Silver was in common use in the Americas when Europeans first arrived.
The Bible contains many references to silver. The metal was used as a way of paying for objects. It also decorated temples, palaces, and other important buildings. The Bible also contains sections that describe the manufacture of silver.
The word silver goes back to at least the 12th century, A.D. It seems to have come from an old English word used to describe the metal, seolfor. The symbol for silver (Ag), however, comes from its Latin name, argentum. The name may have originated from the Greek word argos,meaning "shiny" or "white."

Physical properties

Silver is a soft, white metal with a shiny surface. It is the most ductile and most malleable metal. Ductile means capable of being drawn into thin wires. Malleable means capable of being hammered into thin sheets. Silver has two other unique properties. It conducts heat and electricity better than any other element. It also reflects light very well.

Hot, glowing silver.

Silver's melting point is 961.5°C (1,762°F) and its boiling point is about 2,000 to 2,200°C (3,600 to 4,000°F). Its density is 10.49 grams per cubic centimeter.

Drawings on some of the oldest pyramids show men working with metal, probably extracting silver from its ores.

Chemical properties

Silver is a very inactive metal. It does not react with oxygen in the air under normal circumstances. It does react slowly with sulfur compounds in the air, however. The product of this reaction is silver sulfide (Ag ₂S), a black compound. The tarnish that develops over time on silverware and other silver-plated objects is silver sulfide.
Silver does not react readily with water, acids, or many other compounds. It does not burn except as silver powder.

Occurrence in nature

Silver is a fairly rare element in the Earth's crust. Its abundance is estimated to be about 0.1 parts per million. It is also found in seawater. Its abundance there is thought to be about 0.01 parts per million.
Silver usually occurs in association with other metal ores, especially those of lead . The most common silver ores are argentite (Ag ₂S); cerargyrite, or "horn silver" (AgCl); proustite (3Ag ₂S ○ As ₂S ₃); and pyrargyrite (Ag ₂S ○ Sb ₂S ₃).
The largest producers of silver in the world are Mexico, Peru, the United States, Canada, Poland, Chile, and Australia. In the United States, silver is produced at about 76 mines in 16 states. The largest state producers are Nevada, Idaho, and Arizona. These three states account for about two-thirds of all the silver mined in the United States.

Isotopes

Two naturally occurring isotopes of silver exist: silver-107 and silver-109. Isotopes are two or more forms of an element. Isotopes differ from each other according to their mass number. The number written to the right of the element's name is the mass number. The mass number represents the number of protons plus neutrons in the nucleus of an atom of the element. The number of protons determines the element, but the number of neutrons in the atom of any one element can vary. Each variation is an isotope.
About 16 radioactive isotopes of silver are known also. A radioactive isotope is one that breaks apart and gives off some form of radiation. Radioactive isotopes are produced when very small particles are fired at atoms. These particles stick in the atoms and make them radioactive.
None of the radioactive isotopes of silver has any commercial use.

The tarnish that develops over time on silverware and other silver-plated objects is silver sulfide.

Extraction

Ores rich in silver disappeared long ago due to mining. Today, silver usually comes from ores that contain very small amounts of the metal. These amounts can range from about a few thousandths

A small percent of silver produced in the United States is used for coins. The old "Peace" silver dollar, shown here, was minted from 1921 to 1935.

of an ounce per ton of ore to 100 ounces per ton. The metal is most commonly produced as a by-product of mining for other metals. After the primary metal has been removed, the waste often contains small amounts of silver. These wastes are treated with chemicals that react with the silver. The silver can then be extracted by electrolysis. Electrolysis is a process by which a compound is broken down by passing an electric current through it.

Uses and compounds

About 10 percent of silver produced in the United States is used in coins, jewelry, and artwork. One way silver is used is in alloys with gold. Gold is highly desired for coins and jewelry. But it is much too soft to use in its pure form. Adding silver to gold, however, makes an alloy that is much stronger and longer lasting. Most "gold" objects today are actually alloys, often alloys of silver and gold.
Other objects use much more of the silver metal, however. About half of the silver produced in the United States goes into photographic film. Pure silver is first converted to a compound: silver chloride, silver bromide, or silver iodide. The compound is then used to make photographic film (see accompanying sidebar).
The second most important use of silver is in electrical and electronic equipment. About 20 percent of all silver produced is used for this purpose. Silver is actually the most desirable of all metals for electrical equipment. Electricity flows through silver more easily than it does through any other metal. In most cases, however, metals such as copper or aluminum are used because they are less expensive.

Silver's important role in film

T aking a photograph depends on a simple chemical idea: Light can cause electrons to move around. Here is what that means:
Silver metal will combine with chlorine, bromine, or iodine to form compounds. As an example:
In this reaction, each silver atom loses one electron to a chlorine atom. The silver atom becomes "one electron short" of what it usually has. The one-electron-short silver atom is called a silver ion.
Photographic film is coated with a thin layer of silver chloride, silver bromide, or silver iodide. That means the film is covered with many silver ions. Silver ions are colorless, so photographic film has no color to it.
What happens when photographic film is exposed to light? Light gives energy to electrons in the photographic film. Some of these electrons find their way back to silver ions, transforming them back to atoms:
But silver atoms are not colorless. They are black. So, a photographic film exposed to light turns black at every point where light strikes a silver ion.
In taking a picture, of course, not all of the film gets equal amounts of light. A picture of a person, for example, will have areas that get much more light than others. So some places on the film become very dark, and other places become less dark.
Additional steps are necessary to "develop" photographic film or to produce a picture from it. But the first step in taking a photograph is changing silver ions back to silver atoms with light.

But sometimes, an electrical device is so important that cost is not a consideration. For example, electrical devices on spacecraft, satellites, and aircraft must work reliably and efficiently. The cost of using silver is not as important as it would be in a home appliance. Thus, silver is used for electrical wiring and connections in these devices.
In some cases, silver plating solves a practical problem where the more expensive silver would work best. Silver plating is the process by which a very thin layer of silver metal is laid down on top of another metal. Silver is so malleable that it can be hammered into sheets thinner than a sheet of paper. Silver this thin can be applied to another metal. Then the other metal takes on some of the properties of the silver coating. For example, it may work very well as a reflector because silver is such a good reflector. It does not matter if the second metal is a good reflector or not. The silver coating serves as the reflecting surface in the combination.
About a fifth of all silver produced is used in a variety of other products. For example, it is often used in dental amalgams. An amalgam is an alloy in which mercury is one of the metals used. Silver amalgams work well for filling decayed teeth. They are non-toxic and do not break down or react with other materials very readily. Silver is also used in specialized batteries, including silver- zinc and silver- cadmium batteries.

Electricity flows through silver more easily than it does through any other metal.

Health effects

Silver is a mildly toxic element. When the metal or its compounds get on the skin, they can cause a bluish appearance known as argyria or argyrosis. Breathing in silver dust can have serious long-term health effects also. The highest recommended exposure for silver dust is 0.1 milligrams per cubic meter of air.

An Introduction Manganese

2011-09-18T19:10:00.001-07:00

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Overview

Manganese is a transition metal. The transition metals are the large block of elements in the middle of the periodic table. The periodic table is a chart that shows how chemical elements are related to each other. The transition metals make up Rows 4 through 7 in Groups 3 through 12 of the periodic table. Many of the best known and most widely used metals are in this group of elements.
It took chemists some time to discover the difference between manganese and iron. The two metals have very similar properties and often occur together in the Earth's crust. The first person to clearly identify the differences between the two elements was Swedish mineralogist Johann Gottlieb Gahn (1745-1818) in 1774.

SYMBOL
Mn
ATOMIC NUMBER
25
ATOMIC MASS
54.9380
FAMILY
Group 7 (VIIB)
Transition metal
PRONUNCIATION
MANG-guh-neez

Manganese plays an interesting role in the U.S. economy. It is absolutely essential in the production of iron and steel. No element has been found that can replace manganese is such applications. The United States has essentially no manganese supplies of its own, so it depends on imports from other nations.

Discovery and naming

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One of the main ores of manganese is pyrolusite. Pyrolusite is made up primarily of the compound manganese dioxide (MnO ₂). Early artists were familiar with pyrolusite. They used the mineral to give glass a beautiful purple color. They also used the mineral to remove color from a glass. When glass is made, it often contains impurities that give the glass an unwanted color. The presence of iron, for example, can give glass a yellowish tint. Adding pyrolusite to yellowish glass removes the color. The purple tint of pyrolusite balances out the yellow color of the glass. The glass ends up being clear and colorless.
By the mid-1700s, chemists began to suspect that pyrolusite might contain a new element. Some authorities credit German chemist Ignatius Gottfried Kaim with isolating the element in 1770. However, Kaim's report was not read by many chemists and was quickly lost.
During this period, some of the most famous chemists in Europe were trying to analyze pyrolusite, but none of them was successful. The problem was solved in 1774 when Gahn developed a method for removing the new element from pyrolusite. He heated pyrolusite with charcoal (pure carbon ). The carbon tookoxygen away from manganese dioxide, leaving behind pure manganese:
The origin of manganese's name is a bit confusing. Early chemists associated the new element with a mineral called magnesia. That mineral got its name because it is magnetic. Magnesia does not contain manganese, but the name stuck.

Physical properties

Manganese is a steel-gray, hard, shiny, brittle metal. It is so brittle, in fact, that it cannot be machined in its pure form. Machining refers to the bending, cutting, and shaping of a metal by mechanical means. The melting point of manganese is 1,245°C (2,273°F) and its boiling point is about 2,100°C (3,800°F). Its density is 7.47 grams per cubic centimeter.
Manganese exists in four allotropic forms. Allotropes are forms of an element with different physical and chemical properties. The element changes from one form to another as the temperature rises. The form that exists from room temperature up to about 700°C (1,300°F) is the most common form.

Chemical properties

Manganese is a moderately active metal. It combines slowly with oxygen in the air to form manganese dioxide (MnO ₂). At higher temperatures, it reacts more rapidly. It may even burn, giving off a bright white light. Manganese reacts slowly with cold water, but more rapidly with hot water or steam. It dissolves in most acids with the release of hydrogen gas. It also combines with fluorine and chloride to make manganese difluoride (MnF ₂) and manganese dichloride (MnCl ₂).

Occurrence in nature

Manganese never occurs as a pure element in nature. It always combines with oxygen or other elements. The most common ores of manganese are pyrolusite, manganite, psilomelane, and rhodochrosite. Manganese is also found mixed with iron ores. The largest producers of manganese ore in the world are China, South Africa, the Ukraine, Brazil, Australia, Gabon, and Kazakstan.
Manganese also occurs abundantly on the ocean floor in the form of nodules. These nodules are fairly large lumps of metallic ores. They usually contain cobalt, nickel, copper, and iron, as well as manganese. Scientists estimate that up to 1.5 trillion metric tons of manganese nodules may lie on the floors of the world's oceans and large lakes. Currently, there is no profitable method for removing these ores.
Manganese is the 12th most abundant element in the Earth's crust. Its abundance is estimated to be 0.085 to 0.10 percent. That makes it about as abundant as fluorine or phosphorus.

Up to 1.5 trillion metric tons of manganese nodules (large lumps of metallic ores) may lie on ocean floors.

Isotopes

Only one naturally occurring isotope of manganese exists, manganese-22. Isotopes are two or more forms of an element. Isotopes differ from each other according to their mass number. The number written to the right of the element's name is the mass number. The mass number represents the number of protons plus neutrons in the nucleus of an atom of the element. The number of protons determines the element, but the number of neutrons in the atom of any one element can vary. Each variation is an isotope.

Men and machine lay railroad tracks. A common alloy of manganese, ferromanganese, is contained in the steel used to produce railroad tracks.

Nine radioactive isotopes of manganese are known also. A radioactive isotope is one that breaks apart and gives off some form of radiation. Radioactive isotopes are produced when very small particles are fired at atoms. These particles stick in the atoms and make them radioactive.
None of the radioactive isotopes of manganese has any important commercial uses.

Extraction

The usual method for producing pure manganese is to heat manganese dioxide (MnO ₂) with carbon or aluminum. These elements remove the oxygen and leave pure metal:

Uses

Up to 90 percent of all manganese produced is made into steel alloys. An alloy is made by melting and mixing two or more metals. The mixture has properties different from those of the individual metals. The addition of manganese to steel makes the final product hard, as well as resistant to corrosion (rusting) and mechanical shock.

The heavy steel found in bank vaults contains ferromanganese, a manganese alloy.

The most common alloy of manganese is ferromanganese. This alloy contains about 48 percent manganese combined with iron and carbon. Ferromanganese is the starting material for making a very large variety of steel products, including tools, heavy-duty machinery, railroad tracks, bank vaults, construction components, and automotive parts. About 60 percent of the manganese used in the United States in 1996 went to the manufacture of ferromanganese.
Another common alloy of manganese is silicomanganese. It contains manganese, silicon, and carbon in addition to iron. It is used for structural components and in springs. The production of silicomanganese accounted for about 33 percent of the manganese used in the United States in 1996.
Manganese is also used to make alloys with metals other than iron or steel. For example, the alloy known as manganin is 84 percent copper, 12 percent manganese, and 4 percent nickel. Manganin is used in electrical instruments.

Compounds

Less than 10 percent of all the manganese used in the United States goes to the production of manganese compounds. Perhaps the most important commercial use of these compounds is manganese dioxide (MnO ₂). Manganese dioxide is used to make dry-cell batteries. These batteries are used in electronic equipment, flashlights, and pagers. Dry cell batteries hold a black pasty substance containing manganese dioxide. The use of manganese dioxide in a dry cell prevents hydrogen gas from collecting in the battery as electricity is produced.
Another manganese compound, manganous chloride (MnCl ₂), is an additive in animal food for cows, horses, goats, and other domestic animals. Fertilizers also contain manganous chloride so that plants get all the manganese they need.
Finally, small amounts of manganese compounds are used as coloring agents in bricks, textiles, paints, inks, glass, and ceramics. Manganese compounds can be found in shades of pink, rose, red, yellow, green, purple, and brown.

Health effects

Manganese is one of the chemical elements that has both positive and negative effects on living organisms. A very small amount of the element is needed to maintain good health in plants and animals. The manganese is used by enzymes in an organism. An enzyme is a molecule that makes chemical reactions occur more quickly in cells. Enzymes are necessary to keep any cell operating properly. If manganese is missing from the diet, enzymes do not operate efficiently. Cells begin to die, and the organism becomes ill.
Fortunately, the amount of manganese needed by organisms is very small. It is not necessary to take extra manganese to meet the needs of cells.

Manganous chloride (MnCl ₂) is an additive in animal food.

In fact, an excess of manganese can create health problems. These problems include weakness, sleepiness, tiredness, emotional disturbances, and even paralysis. The only way to receive such a large dose is in a factory or mine. Workers may inhale manganese dust in the air.

extraction of cu for IIITJEE

2011-09-18T18:37:00.000-07:00

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COPPER

This page looks at the extraction of copper from its ores, its purification by electrolysis, and some of its uses. Extracting copper from its ores The method used to extract copper from its ores depends on the nature of the ore. Sulphide ores such as chalcopyrite are converted to copper by a different method from silicate, carbonate or sulphate ores. Getting copper from chalcopyrite, CuFeS₂ Chalcopyrite (also known as copper pyrites) and similar sulphide ores are the commonest ores of copper. The ores typically contain low percentages of copper and have to be concentrated by, for example, froth flotation before refining.
	Note: You will find a brief description of froth flotation on theintroduction to metal extraction page.
The process The concentrated ore is heated strongly with silicon dioxide (silica) and air or oxygen in a furnace or series of furnaces. The copper(II) ions in the chalcopyrite are reduced to copper(I) sulphide (which is reduced further to copper metal in the final stage). The iron in the chalcopyrite ends up converted into an iron(II) silicate slag which is removed. Most of the sulphur in the chalcopyrite turns into sulphur dioxide gas. This is used to make sulphuric acid via the Contact Process. An overall equation for this series of steps is: The copper(I) sulphide produced is converted to copper with a final blast of air.
	Warning! This is a simplified version of the process - an attempt to condense the whole thing down to two fairly straightforward equations. The problem is that there are all sorts of variations on this extraction. One of these does the whole thing in a single furnace, and the equations above probably best represent that particular process. This quick summary is probably unsuitable for anything other than UK A level purposes. If you are working at a higher level, or want proper technical details of particular methods, you will need to look elsewhere. Good luck doing this! I found internet sources fairly unhelpful. Several chemistry sites gave a method which is hardly used nowadays. Other sites give technical details, but no equations. I didn't find a good source of both!
The end product of this is called blister copper - a porous brittle form of copper, about 98 - 99.5% pure. Exploring the redox processes in this reaction It is worthwhile spending some time sorting out what the reducing agent is in these reactions, because at first sight there doesn't appear to be one! Or, if you look superficially, it seems as if it might be oxygen! But that's silly!
	Note: You aren't going to make much sense of this next bit if you don't have a good working knowledge of oxidation states (oxidation numbers). If you aren't sure, then either follow this link (which could take you some time) or skip this bit completely if you don't need to be able to do it. If you choose to follow this link, use the BACK button on your browser to return to this page later.
We'll start by looking at the second reaction because it is much easier to see what is happening. Let's look at the oxidation states of everything. In the copper(I) sulphide, the copper is +1 and the sulphur -2. The oxidation states of the elements oxygen (in the gas) and copper (in the metal) are 0. In sulphur dioxide, the oxygen has an oxidation state of -2 and the sulphur +4. That means that both the copper and the oxygen have been reduced (decrease in oxidation state). The sulphur has been oxidised (increase in oxidation state). The reducing agent is therefore the sulphide ion in the copper(I) sulphide. The other reaction is more difficult to deal with, because you can't work out all of the oxidation states by following the simple rules - there are too many variables in some of the substances. You have to use some chemical knowledge as well. In the CuFeS₂, you would have to know that the copper and iron are both in oxidation state +2, for example. You would also have to know that the oxidation state of the silicon remains unchanged at +4. So use that information to work out what has been oxidised and what reduced in this case! You should find that copper has been reduced from +2 to +1; oxygen (in the gas) has been reduced from 0 to -2 (oxygen in the SiO₂ is unchanged); and three of the four sulphurs on the left-hand side have been oxidised from -2 to +4 (the other is unchanged). Once again, the sulphide ions are acting as the reducing agent. Extracting copper from other ores Copper can be extracted from non-sulphide ores by a different process involving three separate stages: Reaction of the ore (over quite a long time and on a huge scale) with a dilute acid such as dilute sulphuric acid to produce a very dilute copper(II) sulphate solution. Concentration of the copper(II) sulphate solution by solvent extraction. The very dilute solution is brought into contact with a relatively small amount of an organic solvent containing something which will bind with copper(II) ions so that they are removed from the dilute solution. The solvent mustn't mix with the water. The copper(II) ions are removed again from the organic solvent by reaction with fresh sulphuric acid, producing a much more concentrated copper(II) sulphate solution than before. Electrolysis of the new solution. Copper(II) ions are deposited as copper on the cathode (for the electrode equation, see under the purification of copper below). The anodes for this process were traditionally lead-based alloys, but newer methods use titanium or stainless steel. The cathode is either a strip of very pure copper which the new copper plates on to, or stainless steel which it has to be removed from later. Purification of copper When copper is made from sulphide ores by the first method above, it is impure. The blister copper is first treated to remove any remaining sulphur (trapped as bubbles of sulphur dioxide in the copper - hence "blister copper") and then cast into anodes for refining using electrolysis. Electrolytic refining The purification uses an electrolyte of copper(II) sulphate solution, impure copper anodes, and strips of high purity copper for the cathodes. The diagram shows a very simplified view of a cell. At the cathode, copper(II) ions are deposited as copper. At the anode, copper goes into solution as copper(II) ions. For every copper ion that is deposited at the cathode, in principle another one goes into solution at the anode. The concentration of the solution should stay the same. All that happens is that there is a transfer of copper from the anode to the cathode. The cathode gets bigger as more and more pure copper is deposited; the anode gradually disappears. In practice, it isn't quite as simple as that because of the impurities involved. What happens to the impurities? Any metal in the impure anode which is below copper in the electrochemical series (reactivity series) doesn't go into solution as ions. It stays as a metal and falls to the bottom of the cell as an "anode sludge" together with any unreactive material left over from the ore. The anode sludge will contain valuable metals such as silver and gold. Metals above copper in the electrochemical series (like zinc) willform ions at the anode and go into solution. However, they won't get discharged at the cathode provided their concentration doesn't get too high. The concentration of ions like zinc will increase with time, and the concentration of the copper(II) ions in the solution will fall. For every zinc ion going into solution there will obviously be one fewer copper ion formed. (See the next note if you aren't sure about this.) The copper(II) sulphate solution has to be continuously purified to make up for this.
	Note: If it isn't obvious to you that for every zinc ion going into solution there will be one fewer copper ion, think of it like this. For each copper ion that is deposited as metallic copper at the cathode, two electrons need to flow around the circuit. Where are they coming from? Esentially, it is the anode's job to supply them. They are released there when copper or zinc atoms lose electrons and go into solution as ions. The power source then pumps them around the external circuit to the cathode. So, to deposit one copper ion at the cathode needs two electrons. These can be supplied either by a zinc atom ionising at the anode or by a copper atom ionising - it doesn't need both to happen. That means that for every extra zinc ion that gets into solution there will be one fewer copper ion going in.
Uses of copper Amongst other things copper is used for: electrical wiring. It is a very good conductor of electricity and is easily drawn out into wires. domestic plumbing. It doesn't react with water, and is easily bent into shape. boilers and heat exchangers. It is a good conductor of heat and doesn't react with water. making brass. Brass is a copper-zinc alloy. Alloying produces a metal harder than either copper or zinc individually. Bronze is another copper alloy - this time with tin. coinage. In the UK, as well as the more obvious copper-coloured coins, "silver" coins are also copper alloys - this time with nickel. These are known as cupronickel alloys. UK pound coins and the gold-coloured bits of euro coins are copper-zinc-nickel alloys.

super 30 what is trurh???

2011-09-18T08:56:00.001-07:00

Super-30 founder adds another feather to his cap
Abhay Kumar, Patna, May 12, DHNS:
Founder of Super-30 Anand Kumar will be conferred the ‘Excellence in Education Award-2011’ at a glittering function in Doha on Friday.

Maths wizard Anand, who runs Super-30, an institute which helps the underprivileged students crack the IIT joint entrance examination (JEE), was selected for the award jointly by the Doha chapter of Bihar Foundation and the Indian Association for Bihar & Jharkhand in Doha. These two associations are organising a special programme to celebrate the 100th year of Bihar formation. Since its inception in 2002, Super-30 has helped 212 poor students clear the IIT-JEE. For the last three consecutive years, all the 30 students of the institute have made it to the IITs, drawing worldwide attention. Last year, Super-30 was featured by Time magazine as the “best school in Asia.” The Discovery Channel too made an hour-long documentary on the institute, while a film made on it by Christopher Michel went on to win the Viewers’ Choice Award in the USA. Two Japanese Channels have also made films on Super-30. What is remarkable about this institute is that most of the successful candidates have been from the underprivileged sections of the society. Many of them are first generation learners from extremely poor background. They get free food, lodging and above all free coaching. Anand supports the entire exercise by earmarking a portion of his earning through private tuition for the noble cause. “The credit for this goes to my team members and students who strive hard to achieve their goal,” the maths wizard told Deccan Herald.

IIT-JEE: Bihar''s Super 30 cracks cent

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adress of super 30 , bihar by mahendra shukla on Jun 04, 2008 03:02 PM can u provide me adress and contact no of the coaching super 30, what is the admission procedure?? | Report abuse

RE:adress of super 30 , bihar by danish hashmi on Jun 09, 2008 06:40 AM SUPER 30 RAMANUJAN SOCIETY OF MATHEMATICS SHANTI KUTIR, CHANDPUR BELA PATNA- 800 001 (INDIA) email:- mail@super30.org | Report abuse

Super 30 by James Bond on Jun 03, 2008 12:56 PM Do they take a student from other state? james | Report abuse

RE:Super 30 by danish hashmi on Jun 09, 2008 06:41 AM I dont think they take student from outside bihar. But you can take a look on his website or. contact him at the below address SUPER 30 RAMANUJAN SOCIETY OF MATHEMATICS SHANTI KUTIR, CHANDPUR BELA PATNA- 800 001 (INDIA) email:- mail@super30.org | Report abuse

RE:Super 30 by rohit tripathi on Jul 25, 2008 12:57 PM Online IITJEE Preparation | Report abuse

what a fake by mukhlal singh on Jun 02, 2008 06:16 PM Mr. anand kumar a well known mathematician these days, co-founder of super thirty, working for poor students. i cant belive this. i am an ex student of Anank kumar, i had taken mathematics coaching by him when i was preaparing for IIT JEE.He is runnig a huge coaching class behind this free service super thirty.at my time(2002 IIT JEE) in my batch there were 350 students and there was total 7 batches, and fee was RS 2500 . you can calculate how much is the yearly revenu for only one person. and still they have around 3000-4000 students in there coaching institute. today i seen news on INB7 channel,when media person asked Mr. Anand kumar about the money part from where you are getting financial support for doing this great work.. he replied humlog sham me tution padhate hain 11th 12th ke bachhon ke aur usse paisa jo ata hai usse humlog superthirty run karte hai. | Report abuse

RE:what a fake by Tom on Jun 03, 2008 11:48 AM Nothing wrong in what he does. Btw you mean Rs 2500 / month ? This is costlier for students of Patna. | Report abuse

RE:what a fake by mukhlal singh on Jun 03, 2008 12:30 PM i am not saying that. its around 60,00,000 (2500*350*7)buesyness.and out of aound 3000 students if they are producing 30 results then what a big deal. what does it mean to give a free eduaction. they count all successful students from their coaching as super thirty. | Report abuse

Re: RE:what a fake by neeraj singh on May 24, 2009 07:14 PM Mr. Mukhlal...there is absolutely no BIG deal..I don't know why they had to start this Super 30 at all...when there are people like Mukhlal' in the society who can't even see others doing good things in the society...they are, atleast, leveraging the money they earned based on the education they have,..no body stopped you either ..why don't you start something like this...try giving just a Ruppee of your earned money to a needy...sarcasm is not the solution Sir...do & then talk...nothing great that they do...however nothing so great even that could be spoken of you either... | Report abuse

Re: what a fake by Manoj Kumar on Jul 02, 2010 02:26 PM his charges only Rs. 6000 per yaer | Report abuse

great achievement by ganesh chandra on May 31, 2008 04:13 PM super 30 the brain child of one math teacher and the ADG Bihar has given us the live example of grooming of students coming from the lower strata of the society. this is another story after the patwa toli (gaya) achievement in IIT. see this is bihar now the gold mine of IIT, IAS and civil servants coming from all the poor strata of the society. its gives also the inspiration that if one want to change the social fabric the only way out is educational upliftment of the society | Report abuse

Re: great achievement by Guest on Sep 10, 2009 07:29 PM sir, i beg to say that iwant to do iit. .i was doing iit coaching from guidance DELHI .But dwe to my famisly background ileft it . i hope u to s guide me to crack iit | Report abuse

Unsung by chandrasekaran v on May 31, 2008 04:06 PM An important point has been missed in this report. Durng their seven month intensive coaching, students have to strictly stay away from their homes, but they get 'home-made' food prepared by Anand's (Maths teacher)mother Jayanthi Devi. She told TOI that "I offered to prepare food for them so that they kep fit and ocncentrate on theri studies". | Report abuse

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RE:I do not trust by chandrasekaran v on May 31, 2008 03:58 PM I do not think this generalisation, which is doing round for many years, can be applied to IIT-JEE given the system of examination etc. But, I would like to point out that your above post is in the borderline of being reported as abuse. I may also add that another generalisation, going round for many years, is that the Bengalis (I think u hail from West Bengal) would like Biharis/North-Eastern poeple to be subordinate to your folk (hope I am not mistaken). | Report abuse

RE:RE:I do not trust by Dipak Bose on May 31, 2008 04:33 PM Whjat I wrote is particularly applicable for IIT-JEE examination, because only last year West Bengal poilice arrested a large number of Biharis who paid huge money to a company in Bangalore to send experts to sit for these examinations on their behalf. I am sure it is not just Behari, but people from other states are also getting into IITs in this way by hiring experts to sit for them in the examinations, but they got away. This is the way things are working now in India. That is the reason we can see so many hundreds of IAS and IPS officers with the same surname 'KUMAR'. | Report abuse

RE:RE:RE:I do not trust by Gyanendra Prasad on Jun 02, 2008 09:51 AM Hello Mr. Dipak Basu, you are really Bengali. Means full of Jealous(Irshya). Pls. work hard leaving the Irshya your Bang Bhang Samaj also can delight. This is a short note from me. | Report abuse

RE:RE:RE:RE:I do not trust by Dipak Bose on Jun 03, 2008 07:43 AM Those who got admission or jobs by cheating in the examination will continue to cheat all their lives. Only yesterday a number of candidates from Bihar for the Rly recruitment examination were arrested as they also employed experts to sit for the competitive examinations in the Rly recruitment board on their behalf. There were riots a few months ago in Bihar, because in one place the examiners refused to allow cheating supported by local MLA and MPs. | Report abuse

RE:RE:RE:RE:RE:I do not trust by Tom on Jun 03, 2008 12:04 PM You are inventing news. Btw look at your West Bengal. Strike , strike and strike .. u guys have rotten the beautiful calcutta, which british left. Bad days of Bihar are over. It's like, it can't be any more bad. It's destined to become better as it was centuries back, before Muslim invaders attacked it. | Report abuse

RE:RE:RE:I do not trust by Tom on Jun 03, 2008 11:57 AM hmm .. you are ignorant. A Kumar entering IIT by fake means wouldn't be able to survive. But if a Kumar is able to get a degree in IIT , that means he is no fake. It's not possible to do fake things for years and be someone who you are not, specially in IIT. | Report abuse

RE:RE:RE:I do not trust by chandrasekaran v on May 31, 2008 04:42 PM I may add that it is not too late in the case of the recently conducted IIT-JEE also. The authorities can subject the answer-sheets to closer scrutiny especially where complaints of this nature have arisen in the recent past and now. | Report abuse

RE:RE:RE:RE:I do not trust by Dipak Bose on May 31, 2008 05:04 PM You can do nothing by examining the answer scripts as they are all perfect, written by Research Fellows or PhD software engineers who were hired by some companies to sit for the candidates. As I have seen from the reports in the newspapers, the candidates are paying 2-3 Lakhs of Rupees for each set of examinations. This is true for all competitive examinations, possibly also for GMAT/GRE/TOEFL conducted in Indian centres. | Report abuse

RE:RE:RE:RE:RE:I do not trust by himadri roy on Jun 01, 2008 09:15 AM Hi Dipak, As I am away from my country, so I can't say anything about the news you have posted. But what I can say, even if they get into IIT by some ill way, they can't survive over there. It's not about only getting chance, but also about your performance in IIT. Regards Himadri | Report abuse

RE:RE:RE:I do not trust by chandrasekaran v on May 31, 2008 04:40 PM If what you have stated above is true, the authorities conducting IIT-JEE have a lot to reply and also to ensure strict superintendence in the years to come. Thanks for the reply. | Report abuse

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Kudos to Super 30! by Virgo on May 31, 2008 02:19 AM Super 30 has shown the correct path for the upliftment of the downtrodden poor in our society. This also exposes the political rats such as the DMK, Congress, commies and other leftists whose lip service to caste discrimination is just vote bank politics and self agendas. All their ulterior motives came exposed when they opposed the SC decision to drop the creamy layers! The quota system has become perpetual entitlement to the rich and well-off OBC/SC/ST people. The only correct way to eliminate all caste discrimination and help out the downtrodden is to help them with free and high quality education through highschool and base any reservations on the poverty level. Supet 30 has shown the way. I am very happy for the poor students that have made it to the IIT. Congratulations to them and Super30. | Report abuse

RE:Kudos to Super 30! by Vishnu Sharma on May 31, 2008 03:03 AM You are 100% correct. | Report abuse

RE:Kudos to Super 30! by Virgo on May 31, 2008 04:37 AM What is worse is that these creamy later rats, commies and leftists not only are stealing the future of the poor deserving people, in the process, they are instigating and keeping the communal divides of caste, religion etc. alive thus destroying the fabric of Indian society, all for their own seflish agendas. | Report abuse

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RE:This is amazing. CONGRATS. by som ranjan on May 30, 2008 09:42 PM my dear ,never repeat these words to anybody who leaves in these places...what the politeness is of work in DELHI when u can easily it becoming crime capital ....and what the politeness of MUMBAI doing to end the criminals known to world....BIHAR and UP knows how to grow and my dear if u wont get aducated people from your state how can u continue with this legacy of this politeness...plesae hav a look at this my dear | Report abuse

they too have self respect Mr ARJUN SINGH by ashish sinha on May 30, 2008 09:23 PM I so much appreceate this, that derived kids are making into JEE out of their own, without any crutches provided by Mr Arjun Singh. These people will be able to hold their head high. I have seen peope from reservation feeling ashamed of their achievements. I hope ARjun singh and the whole reservation lobby learns a lesson or two, that providing basic facilities is the answer, reservation is not the answer. Its like when you want to make a plant grow, you water the roots, not the leaves. | Report abuse

RE:they too have self respect Mr ARJUN SINGH by mukhlal singh on Jun 02, 2008 06:15 PM Mr. anand kumar a well known mathematician these days, co-founder of super thirty, working for poor students. i cant belive this. i am an ex student of Anank kumar, i had taken mathematics coaching by him when i was preaparing for IIT JEE.He is runnig a huge coaching class behind this free service super thirty.at my time(2002 IIT JEE) in my batch there were 350 students and there was total 7 batches, and fee was RS 2500 . you can calculate how much is the yearly revenu for only one person. and still they have around 3000-4000 students in there coaching institute. today i seen news on INB7 channel,when media person asked Mr. Anand kumar about the money part from where you are getting financial support for doing this great work.. he replied humlog sham me tution padhate hain 11th 12th ke bachhon ke aur usse paisa jo ata hai usse humlog superthirty run karte hai. | Report abuse

Time for Some Idiots to Learn by John Thomas on May 30, 2008 09:04 PM Our Human Resource Minister the great Chamcha Arjun Singh would be wondering how it is all possible without reservation and minority appeasement. | Report abuse

WOW by John Thomas on May 30, 2008 09:03 PM Way to go . IAS, IPS and IIT, People from Bihar are doing well in these areas. | Report abuse

Great!! by zaks hussain on May 30, 2008 08:45 PM Great Sup-30 team!! Your contribution to society will definitely give long term fruit!! KEEP IT UP. | Report abuse

Bihar & Vihar. by Ravindra Yadav on May 30, 2008 08:28 PM After all it was 'Vihar' in Gautama Buddha period which turned now 'Bihar' in Lalu period which knew the cult of 'charvaha-school'from field to factory and office journey, is well planned and ideals set by Lalu & Nitish who come from very backward families and set the best norms of Rail Minister and Chief Minister.In earlier period the state produced leaders like Rajendra Prasad, the first President of India.Jagjivan Ram 'Ex- Dy.Prime Minister of India,Jai Prakash Narain, the sarvodayee leader. | Report abuse

Way to go by deepak on May 30, 2008 08:22 PM Why cant the politicians who divide the country on caste and reservation learn from this?? the way to go is make opportunities available for the underprivileged which is what the Govt should do....not take away the place of a deserving merit by making reservations...foolish Congress have condemned SC/T into perpetual dependence and begging mode. Affirmative action in US more harm than good, same with India. The challenge would be to provide first class schools for deserving sections of socieity which are until now accessible to only the privileged. | Report abuse

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SUPER 30 by jk s on May 30, 2008 08:07 PM The selfless and dedicated work of everybody behind this endeavour makes thousands like me think about what I have contributed. These acts make India a great country. | Report abuse

Congratulations by on May 30, 2008 08:04 PM This is something like miracle for those students have little resource and making it to IIT. This is really a great example spreading the benifits to each section of society. | Report abuse

Obsession with IITs by True Indian on May 30, 2008 08:03 PM Why are people so obsessed with IITs?? Why do you want to waste your life? Try something you are truly interested in. | Report abuse

Congratulations by Fried Yakov on May 30, 2008 07:48 PM I heartily congratualte the commendable achievement by the group at Super 30. If only this can be emulated in other states can we truly change society. It is for all to see how a change in attitude of the peple goes a long way to change society for the better, not the casteist politics of ploiticians. These students, who may b from the lowest social castes, are now well equipped to face the world with their knowledge. Congratulations again. | Report abuse

Salute by Rajesh kumar on May 30, 2008 07:47 PM Salute to Anand and Abhyanand Sir,,, | Report abuse

Lession for Raj T by Eagle on May 30, 2008 07:33 PM Congratulations to all! Hard work and devotion will be the key of success. | Report abuse

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RE:Lession for Raj T by Aditya Phadnis on May 30, 2008 07:38 PM Hmmmm who is Raj T you are refereing too?? did he sit for JEE or is he anyways connected to IIT?? Then whome is this reference in code language directed at? | Report abuse

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wonderful!! by namrata thakur on May 30, 2008 06:56 PM it's great to see such achievement. I had seen it's vidoe on you tube. it's amazing to see the kids of very poor family make it to highest standard of world exams. cracking IIT wich such ease is commendable. ever MIT, harvard and carnegie will salute them. pls keep the good work and see if more poor students can be accomodated and it can be taken to other states too | Report abuse

hats off to you sir by prashant singh on May 30, 2008 06:49 PM I am really proud of you sir.you are a real patriot.Every capable person should take a lesson from you.one should follow your path by implementing the same concept forK.G.S, primary schools,high schools etc for eradicating the illiteracy so that some of them can reach to stature of earning on their own through jobs etc and finally might turn out to be handy in improving the economic and social condition. HATS OFF TO YOU SIR. You are really the nuclear of inspiration. I wish one day i would also be able to do something for others,be it my state Bihar,or Gujrat or Delhi.For that i am going to help myself to be in a position so as can help other I drew lot of inspiration from you. Great Indian in fact great person. | Report abuse

Great Work by vishal on May 30, 2008 06:47 PM Well this reaaly great work! They need to be applauded and supported to further increase their work. This is what we need in todays time and will really make India a great country. Crazy media and useless politicians listening? | Report abuse

Great Achievement by Anand & Abhay by Neutral on May 30, 2008 06:46 PM Kudos to Anand & Abhay for 100% results in the toughest IIT. People like you are required to uplift the downtrodden. This is the real achievement and what is required is these sort of training and coaching instead of reservations Please give your photos to Arjun Singhs & VP Singhs | Report abuse

Read Comments Showing 1 - 10 of total 131 comments

Kudos to the 30 students and their mentors Anand and Abhyanand by Samosachat on May 30, 2008 06:45 PM Keep up the good work. We are so proud of you. Thanks to rediff for publishing a nice happy inspiring story. | Report abuse

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Congratulations ! by Mukesh Kumar on May 30, 2008 06:38 PM Respected Abhayanand Sir and Anand Sir, Congratulations to you and your team for this fantastic achievement. I don't want to say we Bihari's are proud of you, but this means a lot for me. You have setup highest level of social standards for our society. Best wishes and regards, Mukesh Kumar | Report abuse

unsung heroes by subhojit ghosh on May 30, 2008 06:37 PM Aanad Kumar and Abhyanand are the real horoes of modern india.This news item is an eye opener for all those people who think bihar is only about corruption and casteism. | Report abuse

THIS IS A SLAP ON FACE OF PEOPLE LIKE RAJ THAKREY AND HIS SCUM SUPPORTERSby Guest on May 30, 2008 06:37 PM THEY SHOULD SEE HOW INTELLIGENT BIHARIS ARE... THIS YEARS IIT TOPPER IS ALSO BIHARI... BIHARIS AND UPITES ARE IN THE SAME SITUATION INDIANS ARE IN INDIA. INDIANS GO ABROAD AND EARN LOTS, SAME WITH BIHARIS BECAUSE AT HOME EARNING OPPORTUNITY IS NOT THERE...

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Cong should leave vote politics and learn from ANAND by bandu bondu on May 30, 2008 06:35 PMCong should learn from them. Without Vote politics any one can do selfless work. We r proud of anand and his friend | Report abuse

This is the way haves should do for have nots... by A. Swaminathan on May 30, 2008 06:27 PMCongrates..for selfless..work.We need lot more people like Anand.Why we need reservation, spliting the society.

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Result of Super 30 by Rajkumar Kothari on May 30, 2008 06:26 PM These people deserve the highest educational award of the country. Good going.Keep it up.People with financial capability should come forward to support Super 30. | Report abuse

Great doing*** by alok yadav on May 30, 2008 06:26 PM Great work of appreciation . No doubt what ever be caste of this student Super 30 has done a gud job ..

SUPER30 SUCESS STORY by RAMACHANDRARAO MYLAVARAPU on May 30, 2008 06:25 PMWONDERFUL ACHIVEMENT AND REQUEST ALL OUR INDUSTRILISTS TO CONTRIBUTE FOR SUCH CAUSES.IT WILL HELP IN UPLIFTMENT OF BACKWARD AND POOR PEOPLE AND ULTIMATE GROWTH OF INDIA. | Report abuse

What News by sameer pandita on May 30, 2008 06:22 PM I need to be educated on this i guess . Are these backward category students appearing under general category in this exams if so they must be praised for that . If not then this news is not a news to me as they are already having the cushion of reservation easing their way to success | Report abuse

RE:What News by sanjay verma on May 30, 2008 06:44 PM here u r hitting at the right spot. The article is conviniently silent on this aspect. I dont know weather Arjun Singh has provided OBC reservation in this JEE list, but anyway SC/ST reservation is always there. Most regretable is the fact that even rediff like anyother media is trying to sensanalize it, without giving all facts. |

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COMPLEX METAL IONS - LIGAND EXCHANGE REACTIONS

2011-09-18T05:22:00.000-07:00

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This page describes some common ligand exchange (substitution) reactions involving complex metal ions. It assumes that you are familiar with basic ideas about complex ions.
	Note: If you aren't happy about complex ions, then explore the complex ion menu before you go on, or refer back to it if you come across things that you don't understand.
Examples of ligand exchange reactionsA ligand exchange reaction is exactly what it says - a reaction in which one ligand in a complex ion is replaced by a different one. The following examples are taken from UK A' level syllabuses. Replacing water with chloride ions *Replacing the water in the hexaaquacobalt(II) ion* If you add concentrated hydrochloric acid to a solution containing hexaaquacobalt(II) ions (for example, cobalt(II) chloride solution), the solution turns from its original pink colour to a dark rich blue. The six water molecules are replaced by four chloride ions. The reaction taking place is reversible. Concentrated hydrochloric acid is used as the source of chloride ions because it provides a very high concentration compared to what is possible with, say, sodium chloride solution. Concentrated hydrochloric acid has a chloride ion concentration of approximately 10 mol dm^-3. The high chloride ion concentration pushes the position of the equilibrium to the right according to Le Chatelier's Principle.
	Note: You really need to know about Le Chatelier's Principle, particularly with regard to the effect of changes in concentration on the position of equilibrium. Follow this link if you aren't sure.Use the BACK button on your browser to return quickly to this page.
Notice the change in the co-ordination of the cobalt. Chloride ions are bigger than water molecules, and there isn't room to fit six of them around the central cobalt ion. This reaction can be easily reversed by adding water to the solution. Adding water to the right-hand side of the equilibrium has the effect of moving the position of equilibrium to the left. The pink colour of the hexaaquacobalt(II) ion is produced again (only paler, of course, because it is more dilute). *Replacing the water in the hexaaquacopper(II) ion* In terms of the chemistry, this is exactly the same as the last example - all that differs are the colours. Unfortunately, these aren't quite so straightforward. The colour of the tetrachlorocuprate(II) ion is almost always seen mixed with that of the original hexaaqua ion. What you normally see is: The reaction taking place is reversible, and you get a mixture of colours due to both of the complex ions. You may find the colour of the tetrachlorocuprate(II) ion variously described as olive-green or yellow.
	Help! If you dissolve copper(II) oxide in concentrated hydrochloric acid (to make copper(II) chloride which will then go on to form the tetrachlorocuprate(II) ion), you get a dark yellowish brown solution. This probably better reflects the colour of the ion. What are you going to call the colour in an exam? Don't worry about it particularly. Your examiners will almost certainly allow any valid colour. If in doubt look at mark schemes and support material produced by your examiners. If you are a UK A' level student and haven't got these, find out how to get them by visiting the syllabuses page.Use the BACK button (or the History file or the Go menu - depending on how waylaid you get!) to return to this page later.
Adding water to the green solution, replaces the chloride ions as ligands by water molecules again, and the solution returns to blue. Replacing water molecules by ammonia Water molecules and ammonia molecules are very similar in size, and so there is no change in co-ordination this time. Unfortunately, the reactions aren't quite so straightforward to describe. Ammonia solution can react with hexaaqua metal ions in two quite distinct ways, because it can act as a base as well as a ligand. If you add a small amount of ammonia solution you get precipitates of the metal hydroxide - the ammonia is acting as a base. In some cases, these precipitates redissolve when you add more ammonia to give solutions in which a ligand exchange reaction has occurred. In the diagrams below, both steps are shown, but we are only going to consider the chemistry of the overall ligand exchange reaction. The precipitates dissolve because of a complicated series of equilibrium shifts, and we shan't worry about that for the moment.
	Note: You will find full details of the reactions involved in the formation of the precipitates described on a separate page about the reaction of ammonia with metal aqua ions.That page also describes the quite complex reasons why the precipitate dissolves again.
*Replacing the water in the hexaaquacopper(II) ion* This is a slightly untypical case, because only four of the six water molecules get replaced to give the tetraamminediaquacopper(II) ion, [Cu(NH₃)₄(H₂O)₂]²⁺. Notice that the four ammonias all lie in one plane, with the water molecules above and below. What you see in a test tube is: The main equilibrium involved in the ligand exchange reaction is: The colour of the deep blue complex is so strong that this reaction is used as a sensitve test for copper(II) ions in solution. Even if you try to reverse the change by adding large amounts of water to the equilibrium, the strength of the deep blue (even highly diluted) always masks the pale blue of the aqua ion. *Replacing the water in the hexaaquacobalt(II) ion* This time, all the water molecules get replaced. The straw coloured solution formed changes colour very rapidly on standing to a deep reddish brown. The hexaamminecobalt(II) ions are oxidised by the air to hexaamminecobalt(III) ions. However, that is a quite separate reaction, and isn't a part of the ligand exchange reaction. *Replacing the water in the hexaaquachromium(III) ion* Again, all the water molecules get replaced by ammonias. The difference this time is that the reaction isn't so complete. The precipitate has to be left to stand in the presence of excess concentrated ammonia solution for some time in order to get the ammine complex. Even so, you still get left with some unreacted precipitate. Two more replacements of the water in the hexaaquachromium(III) ion The colour of the hexaaquachromium(III) ion has been shown as a "difficult to describe" violet-blue-grey in all the diagrams above. In practice, when it is produced during a reaction in a test tube, it is often green. A typical example of this is the use of acidified potassium dichromate(VI) as an oxidising agent. Whenever this is used, the orange solution turns green and we nearly always describe the green ion as being Cr³⁺_(aq) - implying the hexaaquachromium(III) ion. That's actually an over-simplification. What happens is that one or more of the ligand water molecules get replaced by a negative ion in the solution - typically sulphate or chloride. *Replacement of the water by sulphate ions* You can do this simply by warming some chromium(III) sulphate solution. One of the water molecules is replaced by a sulphate ion. Notice the change in the charge on the ion. Two of the positive charges are cancelled by the presence of the two negative charges on the sulphate ion. *Replacement of the water by chloride ions* In the presence of chloride ions (for example with chromium(III) chloride), the most commonly observed colour is green. This happens when two of the water molecules are replaced by chloride ions to give the tetraaquadichlorochromium(III) ion - [Cr(H₂O)₄Cl₂]⁺. Once again, notice that replacing water molecules by chloride ions changes the charge on the ion.
	Note: Technically, the chloride ion ligand should be written in the formula before the neutral water molecules, but you will find both versions. The one I have chosen to use is probably the more commonly found, and has the advantage that it is consistent with the order the ligands appear in the name.
A ligand exchange reaction in the test for iron(III) ions This provides an extremely sensitive test for iron(III) ions in solution. If you add thiocyanate ions, SCN^-, (from, say, sodium or potassium or ammonium thiocyanate solution) to a solution containing iron(III) ions, you get an intense blood red solution containing the ion [Fe(SCN)(H₂O)₅]²⁺.
	A note on the colours: I haven't been able to suggest properly the intense rich red of the thiocyano complex. Imagine blood!The colour of the original solution isn't the colour of the [Fe(H₂O)₆]³⁺ ion. This is actually very pale violet, but is rarely seen in solution. That complex reacts with water to some extent to produce other more strongly coloured yellow and orange complexes. This is explained in more detail on the page about the acidity of the aqua ions.