ENGINEERING CHEMISTRY

2012-07-01T18:01:00.003+05:30

Chemistry Quiz Questions-(Chemical and elements)

Category - Basic Chemistry I
Question	Correct Answer
An atom is generally regarded as being made up of	Electrons Neutrons Protons
An element is made up of	Atoms
What forms the nucleus of the atom ?	Protons Neutrons
What particles move rapidly around the nucleus ?	Electrons
A pure substance that cannot be split up by a chemical reaction is a	Element
What particle is by far the lightest ?	Electron
Mass Number - Atomic Number =	Number of Neutrons
Mixtures of elements combine to form a	Compound
The mass number is the number of what in an atom ?	Protons Neutrons
The Atomic Number is the total number of what in an atom ?	Protons

GENERAL QUESTIONS :

•H2O is liquid, but H2S is what?

Gas

• Which sulfur has needle shaped crystals?
Prismatic

• Gold paint made from:
Copper

• Name a reducing agent:
Hydrogen sulfide

• Name the dehydrating agent:
Sulfuric acid

• Name a bleaching agent:
Sulfur di oxide

• A rain coat is made up of what?
Polychloroethene

• Which element on adding to natural rubber makes it less sticky in hot weather and less hard in cold weather?
Sulfur

• Which chemical causes Minimata disease?
Mercury

• The absence of cobalt in minute quantities in human body causes what?
Pernicious anemia

• Which element can easily form chains?
Carbon

• Oxygen can accept electron from all elements except what?
Fluorine

• Which element is used as an antichlor?
SO2

• Which is the most reactive element in sixth group?
Oxygen

• Which is the smallest atom in sixth group element?
Oxygen

• All the oxide which contains two atoms of oxygen in a molecule is called what?
Di oxides

• Write example for slow chemical reaction:
Rusting of iron
Change of mill into curd

• Which catalyst used in the manufacture of ammonia from nitrogen and hydrogen?
Iron

• Which substance used as catalyst in the preparation of oxygen from potassium chlorate?
Manganese dioxide

• Which compound formed when hydrogen peroxide decomposes?
Water

• Which useable substance formed as a result of collision?
Active complexes

• Which element can toxic to plants growing in soils that are high acidity?
Aluminum

• Glass is made out of what?
Sand

• Which is considered to be an anomalous compound?
Water

• How would you know that a chemical is pure or not?
By checking its melting point

• Which drug is present in cola drinks?
Caffeine

• Which fuel produce maximum heat per gram burnt?
Hydrogen

• Which element in radioactive form is used for determining the age of artifacts, relics, bones etc. of the past?
Carbon

• Which product of living organisms was the first to be made under the laboratory conditions?
Urea

• Which drug is present in tobacco?
Nicotine

• What is the most common natural source for sulfur?
Volcanic region

• The first scientific definition of a chemical element was made in which book?
The Sceptical Chymist

• Which element is present in the least amount in a living body?
Manganese

• Which substance is produced when nitrogen react with hydrogen?
Ammonia

• Which metal has the density is less than that of water?
Sodium

• Which catalyst used in the manufacture of sulfuric acid?
Vanadium pent oxide

• Which metal react with water and forms an alkaline compound?
Sodium

• Which metal floats on water?
Sodium (potassium)

• Which theory is used for explaining the changes in reaction rate?
Collision theory

2012-07-01T17:31:00.000+05:30

Science Quiz: Chemistry

1) How many moles of sugar are required to make 4 L of a saturated solution of sugar having a concentration of 0.6 mole per liter?
a) 2.4 moles
b) 1.2 moles
c) 1.8 moles
d) 0.6 moles

2) Sugar is not infinitely soluble in water because:
a) when you mix enough sugar into water the solution eventually solidifies.
b) of the strong attractions that occur between sugar molecules
c) of the strong attractions that occur between water molecules
d) there is only so much space between water molecules for sugar molecules to fit

3) Covalent and ionic bonds differ in that:
a) ionic bonds don't involve the sharing of electrons
b) covalent bonds are more permanent
c) covalent bonds are much less common
d) ionic bonds are electrical by nature

4) The outer shells of two atoms that are covalently bonded:
a) cancel each other
b) have increasing capacities for electrons
c) overlap
d) repel

5) The boiling temperature of water is much higher than methane because water molecules are:
a) composed of fewer atoms
b) more massive
c) smaller
d) polar

6) Are there hydrogen bonds between water molecules in the liquid phase?
a) No, and if there were, the water would just be ice (a solid)
b) Yes, and they are continually breaking and reforming
c) Yes, but they rarely occur
d) No, otherwise the water molecules would not be able to tumble over one another

7) Detergents differ from soaps in that:
a) their ionically charged heads are derivatives of sulfur
b) they can be broken down by microorganisms
c) detergents are human-made while soaps are produced naturally
d) detergents are less able to penetrate grease than soaps

8) A pH of 7 signifies a solution which is:
a) basic
b) salt
c) acidic
d) neutral

9) How many different isomers are possible for a hydrocarbon with the molecular formula C4H10?
a) 1
b) 2
c) 3
d) 5

10) Which of these contains the carbonyl group?
a) Ketones
b) Aldehydes
c) Esters
d) All of these

ANSWERS :

1=a
2=d
3=a
4=c
5=d
6=b
7=a
8=d
9=b
10=d

2012-07-01T17:24:00.001+05:30

Sample Questions for the Chemistry Placement Test

The chemistry placement test is used to assess your present level of general chemistry knowledge in addition to your mathematical skills. You will be provided scratch paper (you cannot write on the test itself) and the Periodic Table of the Elements, and you will be allowed to use a calculator. You will have 45 minutes to answer 44 multiple choice questions, with the following sample questions intended only as a guideline:

1. If the formula for potassium chlorate is KClO3 and the formula for magnesium fluoride is MgF2, then what is the formula for magnesium chlorate?
(a) MgClO3
(b) Mg2ClO3
(c) Mg(ClO3)2
(d) Mg2(ClO3)3

2. From the periodic table, what is the atomic number of aluminum?
(a) 26.98
(b) 13
(c) 18
(d) 39.95

3. Which one of the following elements does not exist as a diatomic molecule in nature?
(a) hydrogen
(b) nitrogen
(c) fluorine
(d) neon

For questions 4. and 5., consider the following reaction:
4 Al (s) + 3 O2 (g) ⇒ 2 Al2O3 (s)

4. The reaction can be classified as which one of the following types?
(a) precipitation
(b) decomposition
(c) synthesis
(d) double displacement

5. How many moles of Al2O3 can be produced from the reaction of 10.0 g of Al and 19.0 g of O2?
(a) 0.581 mol
(b) 0.371 mol
(c) 0.185 mol
(d) 0.396 mol

6. What volume of 12.0 M HCl is required to make 75.0 mL of 3.50 M HCl?
(a) 21.9 mL
(b) 0.560 mL
(c) 257 mL
(d) 75.0 mL

7. A fish tank holds 1.029 yd3 of water. What is this volume in cubic meters given that 1 m = 1.093 yd?
(a) 1.062 m3
(b) 0.9414 m3
(c) 1.125 m3
(d) 0.7881 m3
note : m3 and yd3 is the cube representation

8. Which one of the following is a strong acid?
(a) HNO3
(b) CaSO4
(c) NH3
(d) NaOH

For questions 9. and 10., consider the following heating curve of a hypothetical substance:

9. What is the boiling point of the substance?
(a) 0°C
(b) −50°C
(c) 12°C
(d) 75°C

10. What state of matter is the substance at 50°C?
(a) gas
(b) liquid
(c) solid
(d) not enough information

Answers
1. (c) 2. (b) 3. (d) 4. (c) 5. (c) 6. (a) 7. (d) 8. (a) 9. (d) 10. (b)

2012-07-01T17:17:00.000+05:30

Basic concepts of Chemistry

Several concepts are essential for the study of chemistry; some of them are

Atom

An atom is the basic unit of chemistry. It consists of a positively charged core (the atomic nucleus) which contains protons and neutrons, and which maintains a number of electrons to balance the positive charge in the nucleus. The atom is also the smallest entity that can be envisaged to retain the chemical properties of the element, such as electronegativity, ionization potential, preferred oxidation state(s),coordination number, and preferred types of bonds to form (e.g., metallic, ionic, covalent).

Element

The concept of chemical element is related to that of chemical substance. A chemical element is specifically a substance which is composed of a single type of atom. A chemical element is characterized by a particular number of protons in the nuclei of its atoms. This number is known as the atomic number of the element. For example, all atoms with 6 protons in their nuclei are atoms of the chemical elementcarbon, and all atoms with 92 protons in their nuclei are atoms of the element uranium.

Although all the nuclei of all atoms belonging to one element will have the same number of protons, they may not necessarily have the same number of neutrons; such atoms are termed isotopes. In fact several isotopes of an element may exist. Ninety–four different chemical elements or types of atoms based on the number of protons are observed on earth naturally, having at least one isotope that is stable or has a very long half-life. A further 18 elements have been recognised by IUPAC after they have been made in the laboratory.

The standard presentation of the chemical elements is in the periodic table, which orders elements by atomic number and groups them by electron configuration. Due to its arrangement, groups, or columns, and periods, or rows, of elements in the table either share several chemical properties, or follow a certain trend in characteristics such as atomic radius, electronegativity, etc. Lists of the elements by name,by symbol, and by atomic number are also available.

Compound

A compound is a substance with a particular ratio of atoms of particular chemical elements which determines its composition, and a particular organization which determines chemical properties. For example,water is a compound containing hydrogen and oxygen in the ratio of two to one, with the oxygen atom between the two hydrogen atoms, and an angle of 104.5° between them. Compounds are formed and interconverted by chemical reactions.

Substance

A chemical substance is a kind of matter with a definite composition and set of properties.^[38] Strictly speaking, a mixture of compounds, elements or compounds and elements is not a chemical substance, but it may be called a chemical. Most of the substances we encounter in our daily life are some kind of mixture; for example: air, alloys, biomass, etc.

Nomenclature of substances is a critical part of the language of chemistry. Generally it refers to a system for naming chemical compounds. Earlier in the history of chemistry substances were given name by their discoverer, which often led to some confusion and difficulty. However, today the IUPAC system of chemical nomenclature allows chemists to specify by name specific compounds amongst the vast variety of possible chemicals.

The standard nomenclature of chemical substances is set by the International Union of Pure and Applied Chemistry (IUPAC). There are well-defined systems in place for naming chemical species. Organic compounds are named according to the organic nomenclature system.^[39] Inorganic compounds are named according to the inorganic nomenclature system.^[40] In addition the Chemical Abstracts Service has devised a method to index chemical substance. In this scheme each chemical substance is identifiable by a number known as CAS registry number.

Molecule

A molecule is the smallest indivisible portion of a pure chemical substance that has its unique set of chemical properties, that is, its potential to undergo a certain set of chemical reactions with other substances. However, this definition only works well for substances that are composed of molecules, which is not true of many substances (see below). Molecules are typically a set of atoms bound together by covalent bonds, such that the structure is electrically neutral and all valence electrons are paired with other electrons either in bonds or in lone pairs.

Thus, molecules exist as electrically neutral units, unlike ions. When this rule is broken, giving the "molecule" a charge, the result is sometimes named a molecular ion or a polyatomic ion. However, the discrete and separate nature of the molecular concept usually requires that molecular ions be present only in well-separated form, such as a directed beam in a vacuum in a mass spectrograph. Charged polyatomic collections residing in solids (for example, common sulfate or nitrate ions) are generally not considered "molecules" in chemistry.

A molecular structure depicts the bonds and relative positions of atoms in a molecule such as that in Paclitaxel shown here

The "inert" or noble chemical elements (helium, neon, argon, krypton, xenon and radon) are composed of lone atoms as their smallest discrete unit, but the other isolated chemical elements consist of either molecules or networks of atoms bonded to each other in some way. Identifiable molecules compose familiar substances such as water, air, and many organic compounds like alcohol, sugar, gasoline, and the various pharmaceuticals.

However, not all substances or chemical compounds consist of discrete molecules, and indeed most of the solid substances that makes up the solid crust, mantle, and core of the Earth are chemical compounds without molecules. These other types of substances, such as ionic compounds and network solids, are organized in such a way as to lack the existence of identifiable molecules per se. Instead, these substances are discussed in terms of formula units or unit cells as the smallest repeating structure within the substance. Examples of such substances are mineral salts (such as table salt), solids like carbon and diamond, metals, and familiar silica and silicate minerals such as quartz and granite.

One of the main characteristic of a molecule is its geometry often called its structure. While the structure of diatomic, triatomic or tetra atomic molecules may be trivial, (linear, angular pyramidal etc.) the structure of polyatomic molecules, that are constituted of more than six atoms (of several elements) can be crucial for its chemical nature.

Mole and amount of substance

Mole is a unit to measure amount of substance (also called chemical amount). A mole is the amount of a substance that contains as many elementary entities (atoms, molecules or ions) as there are atoms in 0.012 kilogram (or 12 grams) of carbon-12, where the carbon-12 atoms are unbound, at rest and in their ground state.^[41] The number of entities per mole is known as the Avogadro constant, and is determined empirically. The currently accepted value is 6.02214179(30)×10²³ mol⁻¹ (2007 CODATA). One way to understand the meaning of the term "mole" is to compare and contrast it to terms such as dozen. Just as one dozen eggs contains 12 individual eggs, one mole contains 6.02214179(30)×10²³ atoms, molecules or other particles. The term is used because it is much easier to say, for example, 1 mole of carbon, than it is to say 6.02214179(30)×10²³ carbon atoms, and because moles of chemicals represent a scale that is easy to experience.

The amount of substance of a solute per volume of solution is known as amount of substance concentration, or molarity for short. Molarity is the quantity most commonly used to express the concentration of a solution in the chemical laboratory. The most commonly used units for molarity are mol/L (the official SI units are mol/m³).

Ions and salts

An ion is a charged species, an atom or a molecule, that has lost or gained one or more electrons. Positively charged cations (e.g. sodium cation Na⁺) and negatively charged anions (e.g. chloride Cl⁻) can form a crystalline lattice of neutral salts (e.g. sodium chloride NaCl). Examples of polyatomic ions that do not split up during acid-base reactions are hydroxide (OH⁻) and phosphate (PO₄³⁻).

Ions in the gaseous phase are often known as plasma.

Acidity and basicity

A substance can often be classified as an acid or a base. There are several different theories which explain acid-base behavior. The simplest is Arrhenius theory, which states than an acid is a substance that produces hydronium ions when it is dissolved in water, and a base is one that produces hydroxide ions when dissolved in water. According to Brønsted–Lowry acid-base theory, acids are substances that donate a positive hydrogen ion to another substance in a chemical reaction; by extension, a base is the substance which receives that hydrogen ion.

A third common theory is Lewis acid-base theory, which is based on the formation of new chemical bonds. Lewis theory explains that an acid is a substance which is capable of accepting a pair of electrons from another substance during the process of bond formation, while a base is a substance which can provide a pair of electrons to form a new bond. According to concept as per Lewis, the crucial things being exchanged are charges.^[42]^{[unreliable source?]} There are several other ways in which a substance may be classified as an acid or a base, as is evident in the history of this concept ^[43]

Acid strength is commonly measured by two methods. One measurement, based on the Arrhenius definition of acidity, is pH, which is a measurement of the hydronium ion concentration in a solution, as expressed on a negative logarithmic scale. Thus, solutions that have a low pH have a high hydronium ion concentration, and can be said to be more acidic. The other measurement, based on the Brønsted–Lowry definition, is the acid dissociation constant (K_a), which measure the relative ability of a substance to act as an acid under the Brønsted–Lowry definition of an acid. That is, substances with a higher K_aare more likely to donate hydrogen ions in chemical reactions than those with lower K_a values.

Phase

In addition to the specific chemical properties that distinguish different chemical classifications chemicals can exist in several phases. For the most part, the chemical classifications are independent of these bulk phase classifications; however, some more exotic phases are incompatible with certain chemical properties. A phase is a set of states of a chemical system that have similar bulk structural properties, over a range of conditions, such as pressure or temperature.

Physical properties, such as density and refractive index tend to fall within values characteristic of the phase. The phase of matter is defined by the phase transition, which is when energy put into or taken out of the system goes into rearranging the structure of the system, instead of changing the bulk conditions.

Sometimes the distinction between phases can be continuous instead of having a discrete boundary, in this case the matter is considered to be in a supercritical state. When three states meet based on the conditions, it is known as a triple point and since this is invariant, it is a convenient way to define a set of conditions.

The most familiar examples of phases are solids, liquids, and gases. Many substances exhibit multiple solid phases. For example, there are three phases of solid iron (alpha, gamma, and delta) that vary based on temperature and pressure. A principal difference between solid phases is the crystal structure, or arrangement, of the atoms. Another phase commonly encountered in the study of chemistry is theaqueous phase, which is the state of substances dissolved in aqueous solution (that is, in water).

Less familiar phases include plasmas, Bose-Einstein condensates and fermionic condensates and the paramagnetic and ferromagnetic phases of magnetic materials. While most familiar phases deal with three-dimensional systems, it is also possible to define analogs in two-dimensional systems, which has received attention for its relevance to systems in biology.

Redox

It is a concept related to the ability of atoms of various substances to lose or gain electrons. Substances that have the ability to oxidize other substances are said to be oxidative and are known as oxidizing agents, oxidants or oxidizers. An oxidant removes electrons from another substance. Similarly, substances that have the ability to reduce other substances are said to be reductive and are known as reducing agents, reductants, or reducers.

A reductant transfers electrons to another substance, and is thus oxidized itself. And because it "donates" electrons it is also called an electron donor. Oxidation and reduction properly refer to a change in oxidation number—the actual transfer of electrons may never occur. Thus, oxidation is better defined as an increase in oxidation number, and reduction as a decrease in oxidation number.

Bonding

Electron atomic and molecular orbitals

Atoms sticking together in molecules or crystals are said to be bonded with one another. A chemical bond may be visualized as the multipole balance between the positive charges in the nuclei and the negative charges oscillating about them.^[44] More than simple attraction and repulsion, the energies and distributions characterize the availability of an electron to bond to another atom.

A chemical bond can be a covalent bond, an ionic bond, a hydrogen bond or just because of Van der Waals force. Each of these kind of bond is ascribed to some potential. These potentials create the interactions which hold atoms together in molecules or crystals. In many simple compounds, Valence Bond Theory, the Valence Shell Electron Pair Repulsion model (VSEPR), and the concept of oxidation number can be used to explain molecular structure and composition.

Similarly, theories from classical physics can be used to predict many ionic structures. With more complicated compounds, such as metal complexes, valence bond theory is less applicable and alternative approaches, such as the molecular orbital theory, are generally used. See diagram on electronic orbitals.

Reaction

During chemical reactions, bonds between atoms break and form, resulting in different substances with different properties. In a blast furnace, iron oxide, acompound, reacts with carbon monoxide to form iron, one of the chemical elements, and carbon dioxide.

When a chemical substance is transformed as a result of its interaction with another or energy, a chemical reaction is said to have occurred. Chemical reaction is therefore a concept related to the 'reaction' of a substance when it comes in close contact with another, whether as a mixture or a solution; exposure to some form of energy, or both. It results in some energy exchange between the constituents of the reaction as well with the system environment which may be designed vessels which are often laboratory glassware.

Chemical reactions can result in the formation or dissociation of molecules, that is, molecules breaking apart to form two or more smaller molecules, or rearrangement of atoms within or across molecules. Chemical reactions usually involve the making or breaking of chemical bonds. Oxidation, reduction, dissociation, acid-base neutralization and molecular rearrangement are some of the commonly used kinds of chemical reactions.

A chemical reaction can be symbolically depicted through a chemical equation. While in a non-nuclear chemical reaction the number and kind of atoms on both sides of the equation are equal, for a nuclear reaction this holds true only for the nuclear particles viz. protons and neutrons.^[45]

The sequence of steps in which the reorganization of chemical bonds may be taking place in the course of a chemical reaction is called its mechanism. A chemical reaction can be envisioned to take place in a number of steps, each of which may have a different speed. Many reaction intermediates with variable stability can thus be envisaged during the course of a reaction. Reaction mechanisms are proposed to explain the kinetics and the relative product mix of a reaction. Many physical chemists specialize in exploring and proposing the mechanisms of various chemical reactions. Several empirical rules, like the Woodward-Hoffmann rules often come handy while proposing a mechanism for a chemical reaction.

According to the IUPAC gold book a chemical reaction is a process that results in the interconversion of chemical species".^[46] Accordingly, a chemical reaction may be an elementary reaction or a stepwise reaction. An additional caveat is made, in that this definition includes cases where the interconversion of conformers is experimentally observable. Such detectable chemical reactions normally involve sets of molecular entities as indicated by this definition, but it is often conceptually convenient to use the term also for changes involving single molecular entities (i.e. 'microscopic chemical events').

Equilibrium

Although the concept of equilibrium is widely used across sciences, in the context of chemistry, it arises whenever a number of different states of the chemical composition are possible. For example, in a mixture of several chemical compounds that can react with one another, or when a substance can be present in more than one kind of phase.

A system of chemical substances at equilibrium even though having an unchanging composition is most often not static; molecules of the substances continue to react with one another thus giving rise to adynamic equilibrium. Thus the concept describes the state in which the parameters such as chemical composition remain unchanged over time. Chemicals present in biological systems are invariably not at equilibrium; rather they are far from equilibrium.

Energy

In the context of chemistry, energy is an attribute of a substance as a consequence of its atomic, molecular or aggregate structure. Since a chemical transformation is accompanied by a change in one or more of these kinds of structure, it is invariably accompanied by an increase or decrease of energy of the substances involved. Some energy is transferred between the surroundings and the reactants of the reaction in the form of heat or light; thus the products of a reaction may have more or less energy than the reactants.

A reaction is said to be exergonic if the final state is lower on the energy scale than the initial state; in the case of endergonic reactions the situation is the reverse. A reaction is said to be exothermic if the reaction releases heat to the surroundings; in the case of endothermic reactions, the reaction absorbs heat from the surroundings.

Chemical reactions are invariably not possible unless the reactants surmount an energy barrier known as the activation energy. The speed of a chemical reaction (at given temperature T) is related to the activation energy E, by the Boltzmann's population factor - that is the probability of molecule to have energy greater than or equal to E at the given temperature T. This exponential dependence of a reaction rate on temperature is known as the Arrhenius equation. The activation energy necessary for a chemical reaction can be in the form of heat, light, electricity or mechanical force in the form ofultrasound.^[47]

A related concept free energy, which also incorporates entropy considerations, is a very useful means for predicting the feasibility of a reaction and determining the state of equilibrium of a chemical reaction, inchemical thermodynamics. A reaction is feasible only if the total change in the Gibbs free energy is negative, ; if it is equal to zero the chemical reaction is said to be at equilibrium.

There exist only limited possible states of energy for electrons, atoms and molecules. These are determined by the rules of quantum mechanics, which require quantization of energy of a bound system. The atoms/molecules in a higher energy state are said to be excited. The molecules/atoms of substance in an excited energy state are often much more reactive; that is, more amenable to chemical reactions.

The phase of a substance is invariably determined by its energy and the energy of its surroundings. When the intermolecular forces of a substance are such that the energy of the surroundings is not sufficient to overcome them, it occurs in a more ordered phase like liquid or solid as is the case with water (H₂O); a liquid at room temperature because its molecules are bound by hydrogen bonds.^[48] Whereashydrogen sulfide (H₂S) is a gas at room temperature and standard pressure, as its molecules are bound by weaker dipole-dipole interactions.

The transfer of energy from one chemical substance to another depends on the size of energy quanta emitted from one substance. However, heat energy is often transferred more easily from almost any substance to another because the phonons responsible for vibrational and rotational energy levels in a substance have much less energy than photons invoked for the electronic energy transfer. Thus, because vibrational and rotational energy levels are more closely spaced than electronic energy levels, heat is more easily transferred between substances relative to light or other forms of electronic energy. For example, ultraviolet electromagnetic radiation is not transferred with as much efficacy from one substance to another as thermal or electrical energy.

The existence of characteristic energy levels for different chemical substances is useful for their identification by the analysis of spectral lines. Different kinds of spectra are often used in chemicalspectroscopy, e.g. IR, microwave, NMR, ESR, etc. Spectroscopy is also used to identify the composition of remote objects - like stars and distant galaxies - by analyzing their radiation spectra.

2012-07-01T16:58:00.000+05:30

Atom Basics Quiz

Science Fundamentals - 1

The three basic components of an atom are:
(a) protons, neutrons, and ions
(b) protons, neutrons, and electrons
(c) protons, neutrinos, and ions
(d) protium, deuterium, and tritium

An element is determined by the number of:
(a) atoms
(b) electrons
(c) neutrons
(d) protons

The nucleus of an atom consists of:
(a) electrons
(b) neutrons
(c) protons and neutrons
(d) protons, neutrons, and electrons

A single proton has what electrical charge?
(a) no charge
(b) positive charge
(c) negative charge
(d) either a positive or negative charge

Which particles have approximately the same size and mass as each other?
(a) neutrons and electrons
(b) electrons and protons
(c) protons and neutrons
(d) none - they are all very different in size and mass

Which two particles would be attracted to each other?
(a) electrons and neutrons
(b) electrons and protons
(c) protons and neutrons
(d) all particles are attracted to each other

The atomic number of an atom is:
(a) the number of electrons
(b) the number of neutrons
(c) the number of protons
(d) the number of protons plus the number of neutrons

Changing the number of neutrons of an atom changes its:
(a) isotope
(b) element
(c) ion
(d) charge

When you change the number of electrons on an atom, you produce a different:
(a) isotope
(b) ion
(c) element
(d) atomic mass

According to atomic theory, electrons are usually found:
(a) in the atomic nucleus
(b) outside the nucleus, yet very near it because they are attracted to the protons
(c) outside the nucleus and often far from it - most of an atom's volume is its electron cloud
(d) either in the nucleus or around it - electrons are readily found anywhere in an atom

Answers:

^{1 . b}
^{2 . d}
^{3 . c}
^{4 . b}
^{5 . c}
^{6 . b}
^{7 . c}
^{8 . a}
^{9 . b}
^{10. c}

UNIT IV : WATER TECHNOLOGY

2010-03-03T09:11:00.009+05:30

Water : Water is A clear, colorless, odorless, and tasteless liquid, H₂O essential for most plant and animal life and the most widely used of all solvents . Whose Freezing point 0°C (32°F); boiling point 100°C (212°F); specific gravity (4°C) 1.0000; weight per gallon (15°C) 8.338 pounds (3.782 kilograms).

Sources of Water :

(A) Surface Waters : Surface waters generally contains suspended matter , disease producing bacterias .

   1.Rain water : It is obtained as a result of evaporation from the surface water .

   2.River water : Rivers are fed by rain and spring waters . Water from these sources flow over the surface of land .

   3.Lake water : A large inland body of fresh water or salt water. It has a more constant chemical composition .

   4.Sea water : It is the most impure form of natural water . Rivers carry the impurities to the sea .

(B) Underground waters : A part of the rain water which reaches the surface of the earth percolates in to the earth . Spring and well water contains more dissolved salts . Thus water from these sources contains more hardness .

Effects of water on rocks and minerals :

When water flows over/percolates through the ground rocks or solids, It gets contaminated due to the following physical and chemical changes :

1.Dissolution : Mineral constituents of rocks like sodium chloride , gypsum (CaSO4.2H₂O) , etc readily dissolve in water and collect in it .

2.Hydration : Some materials like anhydrite(CaSO4) , olivine (Mg₂SiO₄) , etc . readily undergo hydration , leading to the formation of products of increased volume . It leads to the dis-integration of such mineral breaking rocks . Thus :

- CaSO₄ + 2H₂O ----> CaSO₄.2H₂O (Gypsum of 33% more volume)

- Mg₂SiO₄ + xH₂O ----> Mg₂SiO₄.xH₂O (Serpentine)

3.Action of dissolved oxygen : Oxidation and hydration reactions are brought by dissolved oxygen .

eg:
- 2Fe₃O_{4 (oxd)(+1/2O₂)--->3Fe₂O₃ (Hyd)(2H₂O})---> 3Fe₂O₃.2H₂O (Limonite)
- 2FeS₂+2H₂O+7O₂ (oxd&hyd)----> 2Feso₄+2H₂SO₄

4.Action of dissolved carbon dioxide :

(i) Converts insoluble carbonates of Ca,Mg and Fe into soluble bicorbonates . eg:

- CaCO₃+CO₂+H₂O ---> Ca(HCO₃)₂ (soluble)
- MgCO₃+CO₂+H₂O ---> Mg(HCO₃)₂(soluble)

(ii) Converts insoluble rock-forming silicates and alumino silicates of Na , K , Ca and Fe into soluble carbonates , Bicarbonates and silica.

eg:
K₂O.Al₂O₃.6SiO₂+CO₂+2H₂O ---> Al₂O₃.2SiO₂.2h₂+K₂CO₃+4SiO₂

Dissolved salts , fine clay and silica finally are collected in water .

Electro-dialysis : It is based on the principle that the ions present in the saline water migrate towards their respective electrodes through ion selective membranes . Under the influence of applied e.m.f

Click on the picture for a better view :-)

The unit consists of a chamber , two electrodes , The cathode and anode. The chamber is divided into three compartments with help of thin rigid ion-selective membranes which are permeable to either cation or anion . The anode is placed near anion selective membrane . While the cathode placed near cation selective membrane . The anion selective membrane is containing of positively charged functional groups such as R₄N⁺ and is permeable to anions only . The cation selective membrane consists of negatively charged fucntional groups . Such as RSO₃^-  and is permeable to cations only . Under the influence of applied e.m.f across the electrodes the cations move towards cathode through the membrane and anions move towards anode through the membrane . The net result is depletion of ions in the central compartment while it increases in the cathodic and anodic compartments . Desalinated water is periodically drawn from the central compartment while conc brakish water is replaced with fresh sample .

Advantages :

UNIT I : ELECTRO CHEMISTRY

2009-11-15T14:10:00.064+05:30

Electro-Chemistry :- (def)

The study of chemical applications of electricity is known as Electro-Chemistry . It deals with chemical reaction produced through an electrolyte or production of electricity through chemical reactions .

Conductor : A material that allows electric current to pass through it is known as a conductor .

Types of Conductors :

1) Metallic conductors : In these conductors the flow of electrons is responsible for the passage of electric current and there is no change in physical and chemical nature of the metal .

Eg : Graphite , all metals etc .,

2) Electrolytic conductors : In these conductors current is carried by ions . the electrolyte which is present in either liquid or fused state and the decomposition of electrolyte take place . Eg : H2SO4 , HCl , HNO3 , NaOH , KOH

Ampere : The current which deposits 0.001118 gms of silver per second from a 15% solution of AgNO3 in a voltmeter of definite dimensions .

Coulomb : The quantity of current which passes in 1 second with current strength of 1 ampere is known a a Coulomb .

Ohm : The resistance at 0° c of a column of mercury 106.3 long and weighing 14.4521 gms is known as a Ohm .

Volt : The difference in potential required to send a current of 1 amp strength through 1 ohm resistance is known as a Volt .

Conductance : The conductance of an electrolytic solution is defined a the reciprocal of its own resistance . Conductance is given by L/C = 1/R Its units are ohm^-1(or) mho (or) siemen

Specific conductivity : The conductivity of 1 cm³of solution is known as specific conductivity .

   k = L/a x 1/R = cell constant x Conductance

   UNITS : ohm^-1cm^-1

Equivalent Conductivity : The equivalent conductivity of an electrolyte is defined as the conductance of all ions produced by dissociation of 1gm equivalent of an electrolyte a certain volume V of a solution at constant temperature .

      λ eq or  λ V = K x 1000 / C or N

   Where k = Specific conductivity
   C = conc of solution in gm equivalent per litre

     λ eq = KV and V=1000/C

   UNITS : ohm^-1cm²  eq^-1

Molecular conductivity : It is defined as the conductance of all the ions produced by dissociation of 1 mol wt of an electrolyte dissolved in certain volume V of the solvent at a constant temperature .

     λm = k x 1000 /M

   UNITS : ohm^-1cm²m^-1

Problems :

1) The specific conductivity of a deci-normal solution of an electrolyte is 3 x 10^-4  what is equivalent conductance ???

SOl :   λ eq = k x 1000/c
   = 3 x 10^-4x 10³/ 0.1
     λ eq = 3 ohm^-1cm²  eq^-1

2) Specific conductance of 0.02 normal solution of an electrolyte is 0.004 ohm^-1cm^-1. The resistance of solution is 250 ohms . find the cell constant ???

SOl :    k = L/a x 1/R = cell constant x Conductance

cell constant (L/a) = 0.004 x 250 = 1 cm^-1

3) Resistance of an conductivity cell is found to be 180 ohms & 220 ohms when filled with 0.1 M NaCl & 0.01 N of CuSO4 electrolyte . Calculate the equi conductivity of CuSO4 if the specific conductivity of 0.1 N NaCl solution is 0.0125  ohm^-1cm^-1???

Sol :    k = L/a x 1/R of NaCl
   0.0125 = L/a x 1/180
   L/a = 2.25 cm^-1

   K of CuSO4 = Cell constant / resistance = 2.25/220
   = 0.0102 ohm^-1cm^-1

   λ eq of cuso4 = k x 1000 / 0.01 = 0.0102 x 1000/0.01
   = 1020 ohm^-1cm²  eq^-1

Kohlraush's law : The equivalent conductivity of an electrolyte at infinite dilution is equal to the sum of the equivalent conductivity of its cation and anion

λ eq (at infinite) = λ+(at infinite)  + λ-(at infinite)

APPLICATIONS :

1) Determination of equivalent conductivity at Infinite dilution of weak electrolytes
   Eg: λ eq (at infinite) CH3COOH = λ eq (at infinite) HCl , CH3COONa , NaCl

   λ eq (at infinite) CH3COOH = λ eq(at infinite) [H⁺] +λ eq(at infinite) [Cl^-] +λ eq(at infinite)[CH3COO^-] + λ eq(at infinite) [Na⁺] - λ eq(at infinite) [Na⁺] - λ eq(at infinite) [Cl^-]

   = λ eq(at infinite) [H⁺] +λ eq(at infinite)[CH3COO^-]
   =   λ eq (at infinite) CH3COOH

2) Determination of degree of dissociation : It is the fraction of no. of molecules dissociated into ions .

α (alpha)= No of mol. dissociated into ions / total No of mol. in solution

  α (alpha) = λm^c/λm^αNO UNITS

PROBLEMS on 2nd application:

a) At 25° c the resistance of cell filled with deci-normal KCl solution is 425 ohm the resistance of same cell when filled with 0.1 normal NH4OH is 2300 ohms . The specific conductivity of a deci-normal KCl solution is found to be 0.0012 & equivalent conducatnce of NH4OH at Infinite dilution is found to be 380 ohm^-1cm²  eq^{-1 . What is the degree of dissociation of NH4OH ???}

Sol:    k(kcl) = L/a x 1/R
   0.0012 = L/a x 1/425
   L/a = 0.51 cm^-1

   K(NH4OH) = 0.51/2300 = 2.2 x 10^-4

   λ eq (NH4OH) = k x 1000 / N = 2 x 10^-4x 10³/0.1
   = 2.2 ohm^-1cm²  eq^-1

   Degree of dissociation = 2.2/380 = 0.0057

b) At 20° c equivalent conductivity at infinite dilution of NH4Cl , NaOH , NaCl are 130 , 220 & 110 the equivalent conductivity of 0.01 N NH4OH is 9.20 . calculate the degree of dissociation of NH4OH ???

Sol:  λ eq (NH4OH) = λ eq NH4Cl + λ eq NaOH - λ eq NaCl
   = 130+220+110 = 240

      α (alpha) = λm/λ(infinite)
^{= 9.20/240 = 0.038}

^{3) Determination of solubility of sparingly soluble salt : The conc of sparingly soluble salt is the solubility of the salt .}

     S = k x 1000 /λ(infinite) gm.eq/lit or gm mol/lit
     S = k x 1000 /λm(infinite) x m   gm/lit
     S = k x 1000 /λeq(infinite) x e gm/lit

Problems on 3rd application :

1) The specific conductivity of saturated solution of AgCl at 25° c was found to be 3 x 10^{-6 ohm^-1cm^-1the K of H2) used to make solution 1.6 x 10^-6ohm^-1cm^-1the equivalent conductivity of AgCl at infinite dilution is 140 ohm^-1cm²  eq^-1find the solubility of Agcl in water at 25° c ???}

SOl: K(Agcl) = K(saturated sol of Agcl) - K (H2O)
   = (3.4-1.6) x 10^-6 = 1.8 x10^-6  ohm^-1cm^-1

S = 1.8 x 10^-6x 1000 / 140 = 1.28 x 10^-5 gm.eq/lit

Ionic mobility : It is defined as the total amount of current is carried by any one of the ions .

   Ionic mobility α speed of ions
   Ionic mobility α speed of cations (u)
   Ionic mobility α speed of anions (v)
     Total ions α (u+v)

Under the influence of electric field the cation and anion of electrolyte moves at different speeds and hence carry different amounts of electricity .

     K = 96,500 .
   Ionic mobility = Ionic conductivity / 96,500 cm/sec

since 1 equivalent of an ion under unit potential gradient carrier a charge of 1 Faraday per sec . The proportionality constant k = 96,500 coulombs .

Transport no also directly proportional to the speed of ions

Transport no of cations t+ = U/U+V
Transport no of anions t- = V/U+V

Galvanic cell : an electro chemical cell is a device for converting chemical energy into electrical energy (or) Cell which is used for production of electrical energy from chemical reactions is known as a Galvanic cell . eg: danial cell

CLICK ON THE PICTURE FOR BETTER VIEW :)



The danial cell is a typical example of galvanic cell and consists of copper rod dipping in a solution of CuSO4 which is separated with the help of a semi permeable membrane or a salt bridge from solution of ZnSO4 in which zinc rod is dipped . The Porous wall prevents the diffusion of two liquids but allows the passage of ions through it when the flow of electric current takes place .
OXIDATION : anode: Zn ----->Zn²⁺+2e^-
REDUCTION : cathode: Cu²⁺+ 2e^-----> Cu

The total cell along with the flow of electrons is described as follows :

   E.M.F = 1.09 volts

Concentration Cell : A conc cell is a galvanic cell in which electrical energy is produced by transfer of material from a system of high concentration to low concentration .

TYPES :

1) Electrode conc cell : In these cells the E.M.F arises as a result of two like electrodes at different conc's dipping in the same solution of electrolyte . eg: Two hydrogen electrodes at unequal gas pressures p1&p2 immersed in same solution of H+ ions . The following cell reactions takes place
OXIDATION : H2(p1) ------> 2H+ + 2 electrons
REDUCTION :  2H+ + 2 electrons ------> H2(p2)
TOTAL REACTION: H2(p1) -----> H2(p2)

It is clear that in this process there is no over all chemical change and there is only transfer of H2 gas from electrode with pressure (p1) to the electrode with pressure (p2) . The EMF depends only on pressure and conc of H2 ions solution in which electrodes are dipped .

2) Electrolyte conc cells : These cells consists of two identical electrodes dipped in a two electrolyte solutions of different conc's . A conc cell with 2 ZN electrodes dipped in 2 sloutions of Znso4 with different conc's c1&c2 joined through semi permiable membrane or salt bridge can be represented as follows :

   ZN/ZNSO4(c1) // ZNSO4(c2)/Zn

OXIDATION : Zn(c2) -----> Zn(2+) + 2 electrons
REDUCTION : Zn(2+) + 2 electrons -----> Zn(c1)

The EMF of cell can be calculated by following expression based on nernst equation :

Electrodes :

Single electrode potential (S.E.P) : The potential difference between metal and solution (or) electrode and electrolyte is called Single electrode potential .

Reference electrode : It is an electrode of standard potential with which we can compare the potentials of other electrodes .

TYPES :
1) Primary reference electrode
2) Secondary reference electrode

1) Primary reference electrode : The standard hydrogen electrode is the primary reference electrode . The EMF of such all has orbitally fixed at zero . Hydrogen electrode may be employed to find the P^H  value of unknown solution . The solution whose P^H  value is to be determined is taken in a vessel and platinum electrode is half dipped in it . Hydrogen gas at 1 atmosphere is bubbled through the solution . The platinum catalyses the reaction

   H⁺_(aq) + e^- -----> 1/2 H _{2 (g)}
This reaction develops a definite potential at the electrode depending on the H⁺ions  conc of the solution under test .

The above half cell so formed is connected to a standard or normal Hydrogen electrode . The two solutions are separated by a salt bridge to eliminate liquid junction potential . The EMF of full cell is then determined by means of potentiometer . The EMF of the reference electrode being zero the observed EMF gives directly the EMF of half cell containing solution under test .

2) Secondary reference electrode :

Click on the picture for a better View :-)

Calomel electrode : It consists of tube at bottom where a small amount of Hg is placed . It is covered with a paste of solid Hg2Cl2 . A solution of Kcl is then placed over the paste . A platinum wire dipping into the mercury layer is used for making electrical contact . The side tube is used for making contact with a salt bridge . The saturated calomel electrode is formulated as mercury , Hg2Cl2 , Kcl salt solution . The electrode reaction taking place in the half cell is

   1/2 Hg₂Cl₂ + e^------> Hg + Cl ^-

The electrode can be coupled with H₂electrode containing solution of unknown P^H. The total cell assembly is :

   Pt , H₂/H⁺// KCl.Hg₂Cl₂/Hg

The EMF of the cell is :

Saturated Kcl Reduction potential is 0.2422 Volts , 0.1N Kcl reduction potential is 0.3335 Volts , 1 N Kcl reduction potential is 0.2810 Volts .

Problems :
1) Saturated Kcl Reduction potential is 0.2422 Volts , 0.1N Kcl reduction potential is 0.3335 Volts , 1 N Kcl reduction potential is 0.2810 Volts and the EMF of the following cell at 25° c is 0.445 volts .
   cell : pt,H_{2 (g)}/H⁺//Kcl_(saturated)/Hg₂Cl₂,Hg
Calculate P^H . Given that O.P of saturated calomel electrode is 0.2422 .???

Sol:   E_cell = E_R - E_L
   0.445 = 0.2422 - E_L
     E_L= 0.2422 - 0.4450

   P^H= 0.445 - 0.2422
   _____________
   0.0592

2) What is single electrode potential (S.E.P) of half cell for Zn electrode dipping in a 0.01M Zn solution . E_o= 0.763 Volts . Find Electrode potential of Zn ???

Sol: E= Eo - E(unknown)
     E_((unknown) = - 0.0591 log[0.01]
   --------------
   2
   = -0.0591

   E = 0.763 + 0.0591 = 0.8814

3) Calculate EMF of following reaction at 25° c .
Cu²⁺+Zn -----> Cu + Zn²⁺ .. E^Zn=0.763 V , E^Cu=-0.337

Sol : E= E_R - E_L = 0.763 = 0.337
   = 0.1 Volts

Glass electrode : It is made of a special glass of relatively low M.P and high electrical conductivity . It is a corning glass containing Na2O - 22% , CaO - 6% and SiO2 - 72% . The assembly of glass electrode consists of a thin glass bulb and this electrode is filled with 0.1M HCl and a silver wire coated with AgCl is immersed in it here Ag/AgCl acts as internal reference electrode . The glass electrode is representated as Ag/AgCl/0.1M HCl/Glass .
The measurement of P^H  the Glass electrode is immersed in the solution whose  P^H  is to be determined . It is then combined with a reference saturated calomel electrode . The cell assembly is represented as
Ag/AgCl/0.1M Hcl/Glass/Unknown solution (H+)//Kcl.Hg2Cl2/Hg

The EMF of the cell at 298k is as

     E_cell = E_R - E_L
   = 0.2422-[E_G]+(0.0592 P^H)
   P^H  = 0.2422 -E_cell-E^o_G
   __________________
   0.0592

Glass electrode potential(E^o_G) is 1st measured by dipping the electrode in buffer solution of known P^H values .

ClicK on the picture for a better view :-)

Quin Hydrone electrode : It can be very easily set up by adding a pinch of quin hydrone powder to the experimental solution is stirred until the solution is saturated and a slight excess of it remain undissolved . Then indicator electrode of brigth platinum is inserted in it for determining P^Hvalue this half cell is combined with other reference electrode i.e., saturated calomel electrode and the EMF of cell is determined potentiometrically . The cell is may be represented as
Pt/QH₂ QH⁺//Kcl.Hg2Cl2/Hg⁺

When a platinum electrode is immersed in a solution containing quin hydrone . A potential is established the value of which is given by

E=E^o_Q- 2.303 x 8.318 x 10⁷ x298 Log₁₀ QH₂
   --------------------------------- ----------
   2 x 96,500 [Q][H+]²

The quinone & hydro quinone are taken in equi-molar conc's then
   Quinone = Hydro quinone

Potentiometric Titration's : A titration in which the equivalent or end point of the reaction is determined with help of the potentials of the reaction mixture is known as potentiometric titration .

TYPES:

1) Acid-Base Titration : The acid solution whose strength has to be determined is taken in a beaker and hydrogen electrode and calomel electrode were dipped in the solution with the help of a salt bridge . The electrodes are connected to the potentiometer and EMF is measured . A known volume of standard alkali solution (NaOH) is added from a burette stirred thoroughly and EMF of cell is recorded . Like this 10-15 readings are recorded by repeating the procedure of addition of standard alkali solution . The volume of alkali added is plotted against EMF observed. The sweetest portion of the curve indicates the equivalent point of the solution .

2) Oxidation & Reduction titration : The procedure adopted for oxidation & reduction titration's is same as in acid-base titration's . The only difference is that the electrode reversible to Hydrogen ions is replaced by a bright platinum electrode. The EMF of the electrode is determined by the activity of ratio of substance being oxidised are reduced .
Eg : The Ferrous iron is taken in a beaker and titrated with potassium chromate and platinum electrode and calomel electrode are dipped. The two electrodes are connected to potentiometer (PM) and EMF of solution after addition of potassium chromate . The step rise is the end point of the titration .

3) Precipitation reaction : In these reactions also an electrode reversible to one of the ions involved is made use of , for example : titration of AgNO3 with NaCl where AgCl is precipitated out . Ag electrode is used along the calomel electrode . The AgNO3 is placed in the micro burette and NaCl is taken in a beaker containing electrodes . The EMF of cell is measured and plotted against volume of AgNO3 added . The step rise in the curve shows the end point of the titration .

4) Determination of P^H by EMF method : The EMF of a solution depends on the conc of hydrogen ions or P^H of the solution . A hydrogen electrode containing solution of unknown P^H is paired with a standard calomel electrode . The complete cell may be represented as

   Pt,H₂/H⁺//KCl.Hg₂Cl₂/Hg⁺
The EMF of cell is measured by potentiometer and P^H of unknown solution can be calculated as follows :

Batteries :

Definition : When two or more electro-chemical cells are electrically inter connected each of which consists of 2 electrodes and an electrolyte is called a battery .
Types : There are two types of batteries depending on recharging capacities , they are :
1) Primary batteries /cells (non - rechargeable)
2) Secondary batteries / cells (rechargeable)

1) Primary batteries : These are non-rechargeable and meant for a single use and meant to discharge after the use . Lithium cells belong to this cells . The cells having Lithium can be classified into 2 categories :

a) Lithium cells with solid cathode : In these cells lithium is anode and MnO2 is cathode . The cathode MnO2 should be heated to more than 300^oc to remove water by incorporating it in the cathode . This is very important to improve the efficiency of the battery . The electrolyte is a mixture of propylene carbonate and 1-2 di methoxy methane .
Anodic reaction : Li ------> Li⁺ + e^-
Cathodic reaction : MnO2 + e^-+ Li-----> LiMnO₂
Net reaction : Li + MnO2 ------> LiMnO2

Applications :
1) The cylindrical cells are used in fully automatic cameras .
2) Coil cells are widely used in electronic devices such as calculators , watches .

b) Li cells with liquid cathode : In this cell the cathode constitute 50% - SO2 with solvents such as acrylonytryl or propylene carbonate or mixture of both . The cell reaction can be represented as

Li⁺ + 2SO2 ----> LiS2O4

Thyonil chloride also can be used as a liquid cathode . The cell reaction can be represented as :

4Li + 2SOCl2 ------> 4LiCl + S + SO2

Applications :
1) Used on electronic circuit board for supplying fixed voltage for memory protection and other stand by functions .
2) Used for military and space applications .
3) Used in medical devices such as neuro-stimulator's , drug delivery systems .

2) Secondary Batteries : These are rechargeable and have very large capacitance and long period of low current discharge . eg : Lead acid storage cells & Nickel - cadmium cells .

Lead acid storage cells : This cell has a great advantage of working both as an electrolytic cell and as a voltaic cell . It consists of lead anode and lead dioxide as cathode . Lead dioxide is used in form of a paste . A no of lead plates are connected in parallel and a no of lead di oxide plates are also connected in parallel . The lead plates fit in between lead dioxide plates . The plates are separated by insulators like strips of wood rubber or glass fibre . The entire combination is immersed in 20-21%   dil H2SO4 . The discharging of storage cell is operating as a voltaic cell wher the oxidation of Pb takes place .
Anodic reaction : Pb ----> Pb²⁺ + 2e^-

The Pb²⁺ combines with SO₄^2- (sulphate ions) to produce PbSO4
   Pb²⁺+ SO₄^2- -----> PbSO4

The 2 electrons released at anode close to the lead dioxide electrode and causes reduction of lead dioxide to produce  Pb²⁺which finally combine with SO₄^2- to produce PbSO₄ .

Cathodic reaction : PbO2 + 4H⁺ + 2e^- ------> Pb²⁺ + 2H₂O
   Pb²⁺ + SO₄^2- -------> PbSO4
The lead accumulator for car consists of lead and lead storage cells in series and is capable of delivering 12 Volts . The net reaction is
Pb + PbO2 + 4H⁺ + SO₄^2- -------> 2PbSO4 + 2H₂O + Energy .

Charging : During the charging or re charging an external EMF> 2 volts is passed so that the cell reactions are reversed as
anode : 2PbSO4 + 2e^- ------> Pb + SO₄^2-
Cathode : PbSO4 + 2H₂O + 2e^-  ------> PbO2 + 4H⁺ + SO₄^2- .
Net reaction : 2PbSO4 + 2H₂O + Energy ------> Pb + PbO2 + 4H⁺ + SO₄^2- .

The positive pole of the generator is attached to positive pole of battery and negative pole is connected to the negative pole of the battery of generator . During the discharging operation the conc of H2SO4 decreases while the conc of the acid is restored during charging . Battery containers are made up of hard rubber and palstic .

Applications : Used to supply current for electric vehicles , gas engine ignition in telephone exchanges , electric trains , laboratories , hospitals ,  broad castings stations , auto mobiles , power stations .

Nickel - Cadmium cells : This battery consists of a Cadmium anode and a cathode composed of a paste of NiO(OH) . The cell reactions are

Cd_(s) + 2OH^- -----> Cd(OH)₂ + 2e^-
NiO(OH) + 2e^- + 2H₂O ----> 2Ni(OH)₂ + 2OH^-_{(aq) .}

The reaction can be easily reversed because the reaction products nickel hydroxide & cadmium hydroxide adhere to the electrode surface . Nickel-Cadmium cell give a voltage1.4 V and can be connected in series to give nickel-cadmium storage batteries . There are two types :
1) Pocket - plate Nickel-cadmium battery : The material used for cathode and anode are filled into pocket plates (two perforated nickel coated steel strips) and connected in series . The cells have no longer life i.e., more than 20 yrs with capacities between 10 - 1000 amp and maintains the voltage of 1.4-1.45 Volts .

Click on the picture for better view :-)

2) Sintered plate Nickel-cadmium cells : The cathode materials are finely nickel- sintered in a mould . A Nickel screen impregnated with Nickel nitrate and process to produce Ni(OH)₂ in the course for anode the moulds are impregnated with Cadmium-salt processed to get Cd(OH)₂ . The electrodes are separated by separators such as porous polymer membrane the electrolytic solution is KOH . The sealed cells are made in 2 different designed plates :
1)Horizantal disc (button cells)
2)spirally wound cylindrical cells

Applications :
1) Used for aircrafts & diesel engine starting .
2) lighting of trains .
3) Emergency power supply .
4) many military applications .



Fuel cell : It is an electro chemical cell which converts chemical energy contained in a easily available fuel oxidant system into electrical energy . The basic principle of fuel cells are identical to those of the well known identical cell . The only difference is that in fuel cell the chemical energy is provided by a fuel and an oxidant stored outside the cell .

H₂O₂ Fuel cell  : The cell consists of two inert porous electrodes made of graphite impregnated with finely divided platinum or 75%of alloy of lead with 25% of silver or nickel and an electrolytic solution 2.5% of KOH . Through the anode Hydrogen gas is bubbled and through the cathode Oxygen gas is bubbled . The following reactions takes place :
2H₂ -----> 4H⁺ + 4e^-

O₂ + 4H⁺ + 4e^------> 2H₂O

The product discharged as water and the standard EMF of cell is 1.23 Volts . A no of such fuel cells are stacked together in series to make a battery .

Applications :
1) Used as axillary energy source in space vehicles , sub marines or other military vehicles .
2) Because of light weight these fuel cells are preferred for space craft and product water is valuable space water for astronauts .

Advantages :
1) energy conservation is high 70-82% .
2) The product water is drinking water source for astronauts .
3) noise and thermal pollution are low .
4) fuel cell offer an excellent method for use of fossil fuels .
5) maintenance cause is low, fuel transportation costs , etc., .
6) This cell is an energy storage systems for space applications .

Limitations :
1) the main limitation of fuel cell lie in high initial costs associated with electrode material and design costs . The later could be brought down with mass production and suitable R&D in this direction . The low maintenance and longetivity of cells could compensate some of these negative factors .
2) large weight and volume of Hydrogen gas-fuel storage system .
3) lack of infrastructure for distribution and marketing of hydrogen gas . The developing natural gas distribution net-work could pave way for this in future .
4) High cost of Hydrogen gas . Technological advances should bring the costs down .
5) Most alkaline fuel cells suffer from carbon dioxide leakages and should be properly filtered and prevented from entering the cell and reacting with electrolyte .

UNIT II : Corrosion and its Control

2009-10-02T22:24:00.080+05:30

Corrosion :-(def)

Corrosion is the process of gradual deterioration of metal from its surface due to unwanted chemical or electro chemical reaction of metal with its environment .

Classification :-

Corrosion is classified depending upon the Nature of corrodent,Mechanism of corrosion and Appearence ofCorroaded products

Nature of corrodent :- depending upon thenature of the corrodent Corrosion is classified into two types : (1) Dry Corrosion (2) WetCorrosion

Mechanism of corrosion :- depending upon the mechanism of the corrosion corrosion is classified into two types : (1) Direct chemicalAttack (2) Indirect electro chemical Attack

THEORIES OF CORROSION :

(1) Acid Theory : Carbonic acid(H2CO3) is essential corrosion

REACTION :

Fe(iron) + atm. o (atm.oxygen) + H2O + CO2 ----> Fe(HCO3)2

On OXIDATION of Fe(HCO3)2 :-

2Fe(HCO3)2 + H2O + O2 ------> 2Fe(OH)CO3 + 2H2O + 2CO2

Fe(OH)CO3 + H2O ----> Fe(OH)3 + CO2

(2) Direct Chemical Attack : (Dry corrosion)

Direct chemical attack, or pure chemical corrosion, is an attack resulting from a direct exposure of a bare surface to coustic liquid or gasous agents.

----------> Corrosion by gases : A metal gets Corroaded when they are exposed to gases like atmospheric oxygen , halogens , s02 , H2S, at higher or lower temperatures . alkali metals and alkaline earth metals at lower temperatures and all metals at higher temperatures .

Example : when silver (Ag) metal is exposed to chlorine (Cl2) gas then it gets corroaded and

AgCl is formed .

(3) Electro Chemical Theory / wet corrosion :

Metal corrosion occurs when metal is in contact with conducting liquids when 2 dissimilar metals or alloys are dipped or immersed partially in conducting liquids . It occurs mainly in existance of separate Anode and Cathode areas . At anode oxidation reaction takes place and at Cathode Reduction reaction takes place .

At cathode the electrons are exited in 3 different ways :-

(1) evolution of hydrogen

(2) absorption of oxygen

(3) electro plating

(1) Evolution of Hydrogen : A metal gets corroaded when a metal is placed in an or Exposed to an Acidic Environment by evoloving a Hydrogen atom. Here Metal acts as Anode and the acidic environment acts as Cathode

REACTIONS:

At cathode : Fe ------> Fe(2+) + 2electrons

At Anode : 2H(+) + 2 electrons -------> H2

(2) Absorption of Oxygen : A metal gets corroaded when a metal rod is dipped in dilute solutions like dil.NaCl in a container . A water line is formed in the container . The part of a Metal rod above the water line acts as Cathode because of presence of higher oxygen and the part of a metal rod below water line acts as anode due to presence of low oxygen .

REACTIONS :

Anodic Area reaction :-

oxidation : Fe -------> Fe(2+) + 2 electrons

Cathodic Area reaction :-

reduction: 1/2 O2+H2O+2electrons ---> 2oH(-)

(3) Electro Plating : It is the process of deposition of coating metal on the surface of base metal by flowing the direct current through electrolytic solution consisting soluble salts of the coating metal .

REACTIONS :

Anodic Area reaction :-

oxidation : Fe ----> Fe(2+) + 2 electrons

Cathodic Area reaction :-

reduction: 1/2 O2+H2O+2 electrons ---> 2oH(-)

Types of Wet Corrosion :

(1) Galvanic Corrosion : This corrosion occurs when dissimilar cells are connected and dipped in an electrolytic solution .

Gavanic cells : Cells used for generation of electricity from chemical reactions are called as Galvanic cells or Voltaic cells

Galvanic Couples : (1) zinc & copper (2) zinc & silver (3) iron & copper

(2) Pitting Corrosion : is a form of extremely localized corrosion that leads to the creation of small holes in the metal. The driving power for pitting corrosion is the lack of oxygen around a small area. This area becomes anodic while the area with excess of oxygen becomescathodic, leading to very localized galvanic corrosion. The corrosion penetrates the mass of the metal, with limited diffusion of ions, further pronouncing the localized lack of oxygen. The mechanism of pitting corrosion is probably the same as crevice corrosion.

REACTIONS :

Oxidation : M(metal) -------> M(2+)+2electrons

Note: here the metal taken is IRON(Fe)

Reduction : 1/ 2 O2+ H2O+2electrons ---> 2oH(-)

Total Reaction : Fe(2+) + 2oH(-) --->Fe(OH2) ---> Fe(OH3)

(3) Crevice Corrosion : Crevice corrosion is a localized form of corrosion occurring in spaces to which the access of the working fluid from the environment is limited and a concentration cell, areas with different oxygen concentration, will take place with consequent high corrosion rate . These spaces are generally called crevices. Examples of crevices are gaps and contact areas between parts, under gaskets or seals, inside cracks and seams, spaces filled with deposits and under sludge piles.

(4) Differential Aeration Corrosion :

(or)

Concentration cell Corrosion :

This type of corrosion is caused by anelectrochemical corrosion cell. The potential difference (electromotive force) is causedby a difference in concentration of some component in the electrolyte. Any difference inthe electrolyte contacting the metal forms discrete anode and cathode regions in themetal. Any metal exposed to an electrolyte exhibits a measurable potential or voltage.The same metal has a different electrical potential in different electrolytes, orelectrolytes with different concentrations of any component. This potential differenceforces the metal to develop anodic and cathodic regions. When there is also anelectrolyte and a metallic path, the circuit is complete, current flows, andelectrochemical corrosion will occur.

(OR)

Concentration cell corrosion is corrosion that is accelerated by differences in environment between separated areas on a single metal.

(5) Water Line corrosion : Waterline Corrosion is a form of galvanic corrosion taking place at the surface of a liquid in which the stainless steel is partially immersed.

REACTIONS :

Oxidation : M(metal) -----> M(2+) + 2electrons

Reduction : 1/2 O2+H2O+2electrons ---> 2oH(-)

(6) Underground / Soil Corrosion : This type of corrosion generally occurs in the metal pipes which are buried under the soils . Due to the change in the types of soil the corrosion occurs in the buried pipe . Generally this corrosion occurs in Iron pipes and some other metal rod pipes .

Example: consider a buried Iron pipe as shown in below fig., Here the part of pipe which is under clay soil acts as anode due to the presence of less oxygen (coz the distance b/w the molecules of clay soil is too less) and the part which is under the sand soil acts as cathode due to presence of more oxygen . The corrosion occurs in the anode part

Reactions:

oxidation : Fe ----> Fe(2+) + 2 electrons
reduction: 1/2 O2+H2O+2 electrons ---> 2oH(-)

(7) Passivity/Passivation : It is a phenomenon by which metals or alloys shows highly resistance to corrosion because of formation of protective layer on the surface of metals . Here As there is a protective layer formed it fights or resists with corrosion and help the metal from corrosion . Some metals which show passivity are Nickel(Ni) , Titanium(Ti) , Chromium(Cr) , Aluminum (Al) etc.., these are some of the metals which shows the phenomenon of Passivity .

(8) Stress corrosion/Cracking : The combined effect of static tensil stress and corrosive environment on metal causes Stress corrosion or stress cracking .

Stress corrosive agents are highly specific and selective , Those are :-

1) Caustic alkalies and strong Nitrate solutiuon for mild steel .

2) Traces of Ammonia for Brasses .

3) Acid chloride solution for Stainless steel

Exapmles:

A) Season Cracking : Season crackin is common in copper alloys mainly brasses . When brasses are exposed to Ammonia solution . Both copper and Zinc are electro chemically very active in ammonia solution due to formation of stable complex ions like copper ammonia , zinc ammonia . this is cause of dissolution of brass which ultimately results cracks in presence of high tensile stress .

B) Caustic Embrittilment : It is the phenomenon during which the boiler material become brittle due to the accumulation of caustic substances . This type of boiler corrosion is caused by the use of alkaline water in high pressure boilers sodium carbonate produce caustic substances .

Na2co3+ H2O ------> 2NaOH + CO2

This caustic water close into the minute hair cracks present in the inner side of boiler by capillary action of evaporation of water . The dissolved caustic soda concentration increases progressively which attacks the surrounding area there by dissolving iron of boiler as Sodium ferrate

2NaOH + Fe ----> Na2FeO2+H2

The sodium ferrate decomposes a short distance aware from this point of formation and NaOH is regenerated magnetite is precipitated there by enhancing further dissolution of iron .

3Na2FeO2+4H2O -----> 6NaOH+Fe3O4+H2

This causes embrittlement of boiler walls . More particularly stressed parts like bends . joints , rivets etc . causing failure of the boiler .

Preventive Measures :

1) Caustic embrittlement can be prevented by using sodium phosphate as softening reagent instead of sodium carbonate .

2) Adding tanning or libnin to boiler water which block the hair cracks in the boiler box .

Factors Influencing Corrosion :

A) Nature of the Metal :

1) Position in Galvanic series : When 2 metals or alloys are electrically connected and these are exposed to electrolyte the more active metal suffers from corrosion .

2) Over Voltage : Reduction in over voltage of the metal or alloy acceleratesthe corrosion rate .

Example : Zn occupies a high position in galvanic series is placed in one normal sulfuric acid . Hydrogen evolution takes place rate of corrosion is very slow because of over voltage of zinc(0.70 volts) . However if a few drops of cuso4 are added the corrosion rate of the metal is accelerated because of reduction in over voltage of zinc . i.e., 0.33volts .

3) purity of metal : Lesser is the percentage of purity of metal faster is the rate of corrosion .

4) Relative areas of Anodic & Cathodic parts : The rate of corrosion of metal is less when the area of the cathode is smaller . Then cathodic area is smaller . Then demand for electrons will be less and this results in the decreased rate of dissolution of metal at anodic region .

5) Physical state of the metal : It means orientation of crystals , grain size etc ., . The grain size of the metal or alloy are larger its solubility and corrosion rate is lesser .

6) Nature of the surface field : If the metal is covered by protective film the metal protects the corrosion . If the metal is covered by non protective or volatile field the metal cannot protect the corrosion .

7) Specific volume ratio : It is the ratio of the volume of the metal oxides to the metal . greater the specific volume ratio lesser the oxidation corrosion rate .

8) Passive character of metal : Metals like titanium , aluminium , chromium , magnesium , nickel etc., are passive and they exhibit much higher corrosion resistance because of position in galvanic series and formation of protective layer on the surface of the layer .

9) Solubility of corrosion product : If solubility of corrosion product is more the rate of reaction is also more .

B) Nature of corrosive environment :

1) Temperature : As the temperature increases the rate of corrosion increases .

2) Humidity : With increse of HUmidity the rate of corrosion increases .

3) PH : Corrosion of those metals which are attacked by acids can be reduced by increase in the pH of the specific environment .

4) Presence of impurities in atmosphere : There are some corrosive gases in atmosphere which causes corrosion . the gases like H2SO4 , SO2 , CO2 , Halogens & cubes of sulfuric acid etc ., causes corrosion in metals .

5) Presence of suspended particles in atmosphere : If the metals are exposed to active particles like ammonium sulphate enhance the rate of corrosion . If these are exposed to inactive particles like charcoal it slowly enhances the rate of corrosion .

6) Formation of oxygen concentration cell : Anodic part having lesser oxygen concentration suffers corrosion and corrosion doesnot takes place at cathodic part due to the presence of high oxygen concentration .

Corrosion control methods :

1) Cathodic protection : Let us consider the corrosion of a metal in acidic environment , Metal undergoes corrosion by its oxidation . This reaction is simultaneously accompanied by reduction reaction .

REACTIONS:

Oxidation : M(metal) ----> M⁺²+2e^-(electrons)

Redution : 2H⁺+2e^-(electrons) --->H₂

As its clear from the above reaction we can prevent the dissoultion of metal by forcing the metal to behave like a cathode . This is the principle of Cathodic protection .

Types of Cathodic protection :

A) Sacrificial Anodic protection : The metal structure can be safe from corrosion by connecting it with a copper(Cu) wire to a more active metal so that all the corrosion is concentrated at the more active metal . as the more active metal is sacrificed in the process of saving metal from corrosion . Hence it is known as sacrificial anode .

Metals commonly used as sacrificial anodes are Magnesium , Zinc and thier alloys .

Zinc is used as sacrificial anode in good electrolytes such as sea water .

Magnesium is used as a sacrificial anode in high resistivity electrolytes such as soil .

Applications :

1) Protection of underground cables and pipe lines from soil corrosion .

2) Protection of ships and boats from marine corrosion sheets of Magnesium/Zinc are hung around the SHIP HULL . This sheets being anodic to iron they get corroded and then its consumed completely , those are replaced by the fresh ones

3)The formation of rusty water or water corrosion is prevented by insertion of Magnesium/Zinc sheets or rods into the domestic water tank .

B) Impressed current cathodic protection : In this method current from an external source is impressed (applied in the opposite direction) to nullify the corrosion current . This is done to convert corroding metal from anode to cathode . Once the metal become cathodic it is protected from corrosion . The anode may be either inert material or active material . The anodic materials are Platinum , Graphite , Stailess steel , Scrap iron . The anode is buried in Backfill such as Gypsum to increase the electrical contact between itself and surrounding soil .

Applications :

1)This protection method is useful when electrolyte resisitivity and current requirements are high . It is well suited for large structures and long term obligations such as buried pipe lines, tanks , marine pipes etc.,

2) Surface Coatings : Iron and steel are the most commonly used construction materials due to thier low cost , easy availability , ease of fabrication into desired structures . Iron and steel structures can be protected from corrosion by covering thier surfaces with metallic coatings . The metallic coatings often used are Zn , Al , Tin , Cu , Cd , Cr etc ., these coatings separate the base metal from corrosive environment and also functions as an effective barrier for the protection of base metal .

Types of Surface coatings :

A) Anodic coatings : In this coatings the metal which is used for coating is more anodic than the metal which is to be protected . Anodic coatings protect the underlying base metal sacrificially .

Example : coating of zinc on steel surface .

Let us discuss how galavanised steel is protected from corrosion . here Zn is coating metal and steel is base metal . If any cracks occurs in Zn films . Zn undergoes corrosion because of Zn occupies higher position than steel .

B) Cathode coatings : These coatings protects the underlying base metal due to thier noble character and high corrosion resistance , In such coatings effective protection is possible only when they are completely continuous and free from force , breaks . If the force , breaks are discontinuous occur in such coatings the corrosion of the base metals is speeded up . This is due to the fact that exposed metal acts as anode and coatings become cathode . A galavanic cell is setup and an intense localised at small exposed part occurs . This results in severe pitting and perforation of the base metal .

Methods for applications of Metallic coatings :

1) Hot dipping : It is the process of coating of low melting point metals on the surface of high melting pont materials like iron , steel . This is of two types :-

a) Galvanizing : It is the process of coating of Zinc on the surface of iron or steel . In this process iron or steel is first cleaned by acid picking with dil.H2SO4 for 15-20 minutes and 60-90° c . The article is then washed with water and dries in a dry chamber . It is then dipped in bath of molten Zinc at 425-430°c . The surface of the bath is kept covered with NH3Cl flux to prevent oxide formation . When the article is taken out , the article is coated with a thin layer of Zinc . It is then passed through a pair of hard rollers . This process removes any excess of Zinc on the articles

Click on the picture for a better view :-)

uses : It is widely used for protection of iron and steel from atmospheric corrosion in the form of roofing sheets , wires , pipes , screws , buckets , sheets . Zinc dissolved in dil.acids to form highly tonic compounds . Hence Galvanized utensil cannot be used for storing of food stuff , especially acid ones .

b)Tinning : It is coating of Tin over the iron or steel articles . In this process first treating steel sheet in Dil.H2SO4 to remove any oxide film after this it is passed through a bath of molten tin . It is covered by a Zncl2 flux . This flux helps the molten metal to adhere on the metal sheet and helps to prevent oxidation of molten tin . Finally the metal sheets passed through a series of rollers from underneath the surface of a layer of palm oil . the palm oil protect the hard tin coated surface against oxidation . The rollers remove any excess of tin and produce a tin film of uniform thickness on the steel sheet .

click on the picture for a better view :-)

Uses :

1) Tin coated iron or steel articles or utensils are used for storing and preparing of fodd stuffs .

2) It is most widely used for protection of iron or steel from atmospheric corrosion in the form of roofing sheets , pipes , etc .,

2) Metal cladding : It is a process of coating of brass metal on dense homogeneous layer of cladding material . cladding metals can be pure metals or alloys . In this process arranging Tin sheets of coating metal and the base metal sheet in the form of sandwich which are then passed through rollers under the action of heat and pressure

Example : Duralumin is sandwiched Between two layers of 99.5% pure aluminium . This sheet is called as Alclad used in Aircraft industry .

Electroplating : It is the process of coating of base metal by a dense homogeneous layer of a coating material by passing a direct current through electrolytic solution s consists of soluble

salts of coating metal .

Organic coatings : These are paints , varnishes ,Enamels and lackers .

functions : To impart decorative and aesthetic appeal to give resistance to corrosion .

Paints :

Requirements for a good paint :

1) It should be fluid enough to be spread on the metals surface easily .

2) It should form a quite tough uniform and adherent film .

3)It should have covering or hiding power .

4) It should not crack on drying .

5)It should be corrosion resistance .

6)It should give a glassy film .

Constituents of paints :

Pigments : The most commonly used pigments are yellow pigment like zinc yellow , Brown pigments like clays having iron , green pigments like chromium oxide , red pigments like red lead , black pigments like carbon black , white pigments like Zno2

FUNCTIONS :

1) To provide a desired colour , opacity and strength to the paint .

2) To give protection by reflecting UV light to improve the impermeability of paint film to moisture .

Vehicle or dry oil : It is a film forming constituent of the paint . The liquid portion of the paint in which the pigment is disturbed it is known as Vehicle or dry oil .

FUNCTIONS :

1) They hold the pigment to the metal surface and form a protective film .

2)They give water toughness and durability to the paint .

3)They give better adhesion to the metal surface .

TYPES :

1) Non drying oils - like sunflower oil , mustard oil .

2) semi-drying oils - like fish oil , roxin oil .

3) drying oils - like dehydrated castor oil and limb seed oil .

Tinners : It reduces the viscosity of the paint . They suspend the pigments in the paint . They dissolve the film forming materials . Examples: kerosene , mineral spirits , terpentine etc .,

Dryers : The drying of the oil film is accelerated by driers . They do this by oxidation , polymerisation and condensation .

TYPES :

1) Surface driers eg: Cobalt substances

2) Bottom driers eg: Lead substances

3)Through out driers eg: Manganese substances

Fillers/Extenders : They reduce the cost of the paint . They serve to fill the voids in the paint film . They improve the durability of the film by reducing the cracking of the paints after drying . Eg: CaCO3 , CaSO4 , Gypsum , Asbestos etc .,

Plastisizers : Give elasticity to the paint film and to prevent cracking of the film eg: Tri cresyle phosphate , Tri phenyl phosphate .

Anti skinning agents : This agent prevents the jelling and skinning of paint film . eg: Poly hydroxy phenols .

-----------xxx END OF CORROSION AND ITS CONTROL xxxx--------------

Atom Basics Quiz

ENGINEERING CHEMISTRY

Chemistry Quiz Questions-(Chemical and elements)

Sample Questions for the Chemistry Placement Test

Basic concepts of Chemistry

Atom

Element

Compound

Substance

Molecule

Mole and amount of substance

Ions and salts

Acidity and basicity

Phase

Redox

Bonding

Reaction

Equilibrium

Energy

Atom Basics Quiz Science Fundamentals - 1

UNIT IV : WATER TECHNOLOGY

UNIT I : ELECTRO CHEMISTRY

UNIT II : Corrosion and its Control

-----------xxx END OF CORROSION AND ITS CONTROL xxxx--------------

Atom Basics Quiz

Science Fundamentals - 1