Chemoinsight

Experimental techniques in chemistry

noreply@blogger.com (Mian Tahir) — Fri, 30 Apr 2021 12:33:00 +0500

Experimental techniques in chemistry

Analytical chemistry:

The branch of chemistry which gives a complete characterization of substance that is the qualitative and quantitative analysis of a substance

Qualitative analysis:

The type of analysis in which identification of elements in a compound is carried out for example detection of elements by the sodium fusion test and salt analysis and mixture analysis

Quantitative analysis:

The type of analysis in which relative amounts of different elements are carried out for example volumetric analysis (titration)

The main steps in the quantitative analysis are involved

· Obtaining a sample for analysis

· Separation of the desired component

· Measurement and calculation of the result

· Drawing conclusion from the analysis

Filtration:

The separation of insoluble particles precipitate from the liquid by passing the mixture through a the filter medium is called filtration

Filter medium:

The porous medium which is used to separate insoluble solid particles from a solution or a mixture is called filter medium

Filtrate:

The liquid part of a solution that passed through the filter medium is called filtrate

Residue:

The insoluble particles which cannot pass through the filter medium is called Residue

Selection of a filter medium

· Nature of precipitate

· Size of precipitate

Why fluted filter paper is used instead of normal filter paper

Fluted filter paper increase the rate of filtration because alternate elevations and depressions on a filter paper provides an increased area for filtration Hans it increases the rate of filtration

Differentiate between gooch crucible and sintered glass crucible

Gooch crucible:

Composition: it is made of porcelain having a perforated bottom which is covered with the paper pulp are filter paper are asbestos mat cut to its size. Filtration is useful for the filtration of the precipitate which needs to be ignited at heart temperature. If its perforation is covered with asbestos mad then it may be used to filter solution that reacts with paper

For example: concentrated hydrochloric acid and potassium permanganate solution

Sintered glass crucible: is made up of Glass having a porous glass disc sealed into bottom

Advantages:

It is convenient to use because no preposition is needed as with the crucible moreover the process is very e smooth

Crystallization:

Crystallization is the removal of solid from a solution by increasing its concentration above the saturated point in such a manner that the excess solid separate out in the form of crystals

Why there is a need to crystallize the crude product

There is a need to crystallize the crude product for the purification

Steps of crystallization

• Choice of solvent

• Preparation of saturated solution

• Filtration

• Cooling

• Collecting of crystals

• Drawing to the crystalline substance

• Decolorizing of undesired colors

Write the steps for the choice of solvent in crystallization

• It should dissolve a large amount of a substance at its boiling point and only a small amount at the room temperature

• It should not react chemically with the solute

• It should either not dissolve the imperative are the impurities should not crystallize from it along with the solute

• On cooling it should deposit well-formed crystals of the pure compound

• It should be inexpensive

• It should be safe to use

• It should be easily removable

Note: If none of the solvents is found suitable for crystallization a combination of two or more miscible solvents may be employed

Give the name of drying agents used in the drying of crystallized substance

Drying agents:

• Calcium chloride

• Phosphorus pentoxide

• Silica Gel

Decolorizing of undesirable color:

Sometimes during the preparation of crude substance that coloring matter are resonance product affect the appearance of the product and it may appear color Such color impurities are conveniently removed by boiling the substance in the solvent with the sufficient quantity of finely powdered animal charcoal and then filtering the hot solution impurities are absorbed by the animal charcoal and the pure decolorize substance crystallizes out from the filter on the cooling

How color impurities are removed from crystallized substances

Animal Charcoal is used to decolorize the undesirable color from crystallizing substances

Sublimation:

A process in which a solid when heated vaporized directly without passing through the liquid phase and these vapors can be condensed from the solid again

For example Iodine, ammonium chloride, naphthalene, benzoic acid, and dry ice

Differentiate between sublimand and sublimate

Sublimand:

The substance whose sublimation is required or impure substance for sublimation is called sublimand

Sublimate:

The pure substance after sublimation is called sublimate

Define solvent extraction

Solvent extraction:

The technique in which a solute is separated from a solution by shaking it with an immiscible solvent in which the solute is more soluble is called solvent extraction

Define distribution law

Distribution law:

Solvent extraction is an equilibrium process and it is controlled by distribution law or partition La which is defined as

“A solute distributes itself between two immiscible liquids in a constant ratio of concentration irrespective of the amount of solute added”

Define distribution coefficient K

Distribution Coefficient k:

The ratio of the concentration of solute in an organic solvent to the concentration of solute in an aqueous solution is called distribution Coefficient and it is represented by k

Chromatography:

A process that is used to separate the components of a mixture on the basis of their difference in a relative affinity with two faces that is stationary and the mobile phase is called chromatography

The word chromatography original from the Greek words Chroma toes which means color and graphene which means writing so chromatography means color writing

Differentiate between the stationary phase and mobile phase

Stationary phase:

The stationary phase is a solid or liquid spotted as a thin film on the surface of an inert solid. This phase is in rest and the mobile phase flows over it. Component of a mixture with a small value of k mostly remains in this phase

Example: Glass Silica or Alumina

Mobile phase:

The mobile phase may be liquid or a gas. It flows over the surface of a stationary phase. Component of a mixture with a great value of k mostly remains in this phase

Example: helium argon nitrogen and organic solvents

Distribution coefficient:

The distribution of components of a mixture between the two phases are governed by the distribution coefficient is the ratio of the component in a mobile phase and a concentration of that component in a stationary phase

A smaller value of k:

The component of a mixture with a small value of k mostly remains in the stationary phase and the mobile phase flows over it

The greater value of k:

The component with a the greater value of k largely remains dissolved in the mobile phase and pass over the stationary phase quickly

Types of chromatography

• Adsorption chromatography

• Paper chromatography

Differentiate between adsorption chromatography and partition chromatography

Adsorption chromatography:

A type of chromatography in which the stationary phase is solid. In this type, a substance leaves the mobile Phase to become absorbed on the surface of the solid phase

For example a thin layer chromatography and column chromatography

Partition chromatography:

It is a type of chromatography in which the stationary phase is liquid in this type the a substance being separated are distributed throughout both the stationary and mobile phase

For example paper chromatography

Chromatogram: once the paper is dried the pattern on the paper is called a chromatogram

Retardation factor:

Each component has a specific retardation factor called Rf value this value is related to its distribution Coefficient and is given by

“The ratio between the distance traveled by the component from the originals part and the distance traveled by the solvent from the original spot”

Write important uses of chromatography

Uses of chromatography

It is used for separation and purification

It is used for checking the purity of components

It is used in the qualitative and quantitative analysis

It is used for the separation and identification of colored pigments

It is used for the identification of amino acids

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Quiz for experimental techniques

noreply@blogger.com (Mian Tahir) — Thu, 29 Apr 2021 12:40:00 +0500

Quiz related to experimental techniques

Chemistry Quizzes related to experimental techniques are an important part of different examination especially in board exams and for different university entry text examinations. For good practice and securing good grades in these exams, students should practice this chemistry online quizzes test of experimental techniques

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Short Answers and Questions

noreply@blogger.com (Mian Tahir) — Tue, 27 Apr 2021 11:57:00 +0500

Short Answers and Questions

Basic Concepts

Chapter No.1

Important short answers and questions related to basic concept for first year classes

Question: Define chemistry

Answer:

The branch of chemistry which deals with study of composition, structure, properties and changes of matter and laws and principle that governs these changes is called chemistry

Question: Define Atomicity

Answer:

The number of atoms present in molecule is called atomicity. For example; atomicity of glucose is 24 and atomicity of hemoglobin is 10,000

Question: Why formation of cation is endothermic reaction

Answer:

When an electron is removed from an atom, energy is required to overcome the force of attraction between electrons and nucleus, that’s why formation of cation is an endothermic reaction.

Question: Why formation of anion is an exothermic reaction

Answer:

When an electron is added to an atom, energy is released from an atom due to overcome the force of repulsion between electrons and incoming electron, that’s why formation of anion is an exothermic reaction

Question: Define Molecular Ions

Answer:

Molecules carry both positive and negative charge is called molecular ions

For example CO⁺, O₂^-,

Question: How molecular ions are produced

Answer:

Cation molecular ions are formed by the bombardment of electron beam beta rays alpha rays and X- rays on the gas molecules

Question: Define relative atomic mass

Answer:

Relative atomic mass is the mass of an atom of an element as compare to the mass of atom of carbon taken as 12.

Relative atomic masses are measured in atomic mass unit

Question: Define isotopes

Answer:

The atom of same element having same atomic number but different atomic masses are called isotopes

For example: hydrogen has three isotopes protium, deuterium and tritium

Question: Define empirical formula

Answer:

A formula which shows the simplest whole number ratio between the atoms present in a compound is called empirical formula

For example: benzene CH, glucose CH₂O

Question: Define Molecular formula

Answer:

The formula of substance which is based upon actual number of atoms present in a molecule of a compound is called molecular formula

Example: benzene C6 H6, glucose C₆H₁₂ O

Molecular formula= n x empirical formula

Question: Define mole

Answer:

Atomic mass of an element molecular mass of a molecule formula mass of an ionic substance and ionic mass of ionic species when Express in gram is called mole

23 Graham of sodium = 1 mole

18 Graham of water = 1 mole

58.5 gram of sodium chloride = 1 mole

Question: Write basic assumptions for stoichiometric calculations

Answer:

· All the reactants are completely converted into products

· No side reactions occur

· The reaction must be Irreversible

Question: Write limitation of a chemical equation

Answer:

· Chemical equation does not show the rate of reaction

· It does not tell about the condition necessary for reactions

· The chemical equation can even be written to describe a chemical change that does not occur

Question: Define Limiting Reactant

Answer:

Reactant which is completely consumed earlier leaving behind the other reactant in excess is called limiting reactant

A limiting reactant:

· is consumed earlier

· is in lesser than stoichiometric amount

· Limit the chemical reaction

· Limit the amount of product

· give least amount of product

Question: Write steps to calculate the limiting reactant

Answer:

· Calculate the number of moles from the given amount of reactants

· Find out the number of moles of product with the help of balanced chemical equation

· Identify the reactants which produces the least amount of product as a limiting reactant

Question: Define yield

Answer:

The amount of product calculated from a balanced chemical equation are produced as a result of chemical reaction is known as yield.

Question: Differentiate between theoretical and actual yield

Answer:

Theoretical yield

The amount of product calculated from the balanced chemical equation is called theoretical yield

Actual yield

It is the maximum amount of product that should be produced according to the balanced chemical equation

Question: Why actual yield is less than theoretical yield

Answer:

Side reactions, reversible reactions, incomplete reactions, in experience worker, mechanical loss during separation by, solvent extraction filtration distillation and crystallization and actual yield maybe laser due to inefficiency during the washing and drying of crystals

Question: 23 gram of sodium and 238 gram of Uranium have equal number of atoms in them

Answer:

23 gram of sodium = 1 mole = 6.02 x 10²³ atoms

238 grams of Uranium = 1 mole = 6.02 x 10²³ atoms

That’s why both have equal number of atoms in them

Question: Magnesium atom is twice heavier than that of carbon atom

Answer:

One mole of magnesium = 24 gram

One mole of carbon = 12 gram

That’s why magnesium is twice heavier than carbon atom

Question: 180 gram of glucose and 342 grams of sucrose have same number of molecules but different number of atoms present in them

Answer:

180 grams of glucose = 1 mole = 6.02 X 10²³ molecules

342 grams of sucrose = 1 mole = 6.0 to X 10²³ molecules

One mole of glucose C₆ H₁₂ O₆= 24 atoms

One mole of sucrose C₁₂ H₂₂ O₁₁= 45 atom

That’s why both have same number of molecules both have different number of atoms in them

Question: No individual Neon atom in the sample of the element has a mass of 20.18 amu

Answer:

It is the average atomic mass of different isotopes of different of neon atom in the sample of the element has the mass of 20.18 amu

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Chemistry Online Quiz 2021

noreply@blogger.com (Mian Tahir) — Mon, 26 Apr 2021 11:53:00 +0500

Chemistry Online Quiz 2021

Chemistry online quiz are most important part of every examination. Due to Covid-19 pandemic where physical education in different institution are not conducted and online quiz are the most convenient way to test the ability of students that’s why chemistry online quiz helps to overcome the difficulty in online quiz.

Chemistry Quizzes For Basic Concept

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Chemistry Quizzes

noreply@blogger.com (Mian Tahir) — Sat, 24 Apr 2021 09:31:00 +0500

Chemistry Quizzes

Chemistry Quizzes are important part of different examination especially in board exams and for different university entry text examinations. For good practice and securing good grades in these exams students should practice this chemistry online quizzes test.

Chemistry Online Quizzes For First Year

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Basic Concepts in chemistry

noreply@blogger.com (Mian Tahir) — Thu, 22 Apr 2021 10:06:00 +0500

For thousands of years people rocks and distal plant uses to materials over the past two centuries chemist have loved more and more about how to get materials from rocks from the air and the sea types of plants they have also found out the right condition to alow these materials to react together to make new substances such as dyes, plastic, medicine.

When we make a new substance that is important to mix the reactance in the correct proportions to ensure that it is vested in order to do this we need to know about the relative masses of atoms and molecules and how these are used in chemical calculation.

In order to explain how chemical substances behave, first have to understand but the substances themselves were made from. Over time a model was developed in which all substances were composed of atom of element. Originally it was thought that atom could not themselves be broken up into smaller parts but now we understand the structure inside the atoms themselves and the role of electrons protons and neutrons we cannot design and make materials and objective almost at the atomic level.

Matter

Anything and which has mass and occupy space. For example oxygen nitrogen wood and iron

Atoms

are the smallest particle of an element which may or may not exist independently and it can enter in a chemical reaction for example atoms of Hydrogen oxygen nitrogen do not exist independently but Helium Neon and Argon can exist independently.

Diameter of atom is of the order = 2 x 10^-10 meter or .2 nm.

Radius of atom is of the order = 10^-10

Compound

A pure substance which is formed by the chemical combination of two or more different elements in a fixed ratio by mass is called compound. Hydrogen and Oxygen in water have a fixed ratio by mass which is 1:8 respectively.

Molecules

The smallest particle of an element or compound which exist independently is called molecule

Classification of Molecules

· On the basis of type of atoms

1) Home atomic molecules same kind of atoms H₂, O₃

2) Heteroatomic molecules different kind of atoms HCl , H₂O

· On the basis of number of atoms

1) Monatomic contain only one atom. For Example Helium, Neon, Argon

2) Polyatomic contain more than one atoms. For example O₂ ,CH₄ ,NH₃

· On the basis of mass of molecules

1) Micro molecules: contain molecular mass less than 10000 Dalton. For example glucose

2) Macromolecules: contain molecular mass about 10000 Dalton. For example: protein

Atomicity:

Total number of atoms in one molecule is called atomicity for example hemoglobin has 10000 atom

Ions

The species which carry positive or negative charge. Example Cl^- ,O₂^-,

Types of Ions:

Cations: The ions which carry positive charge. All cations are smaller in size than their parent Atoms and energy is required to form cations. For example: Na^+, Ca⁺⁺

Isoelectronic cations are those have same number of electrons in them.For example Na⁺, Mg⁺⁺, Al⁺⁺⁺

Anions: The ions which carry negative charge. All anions are larger than parent atom andEnergy is released to form anions. For Example: Cl^-,SO₂^-2

Isoelectronic anions are those have same number of electrons in them. For example Cl^-, O^--, N^---

Molecular Ions: Molecules carry positive or negative charge is called molecular ions.For Example: O₂^-2, CH₄⁺

Types of Molecular Ions

Molecular Cations: molecules carry positive charge

Molecular Anions: molecules carry negative charge

Note: NH₄⁺ positive is not a molecular ion:

Moles:

Atomic mass of an element expressed in gram is called gram atom or mole

For example

23 gram of sodium is = 1 mole

12 gram of carbon is = 1 mole

Molar mass of compound expressed in gram is called gram molecule or mole

For example

44 gram of carbon dioxide is = 1 mole

18 gram of water is = 1 mole

Formula mass of ionic compound expressed in gram is called gram formula or mole

For example

58 8.5 gram of sodium chloride is equal to 1 mole

Ionic mass of ions expressed in gram is is called Gram ion or mole

For example

17 gram of OH^- is = 1 mole

Avogadro's number

The number of atoms molecules and ions in 1 mole of substance which is equal to 6.02 x 10 ²³. It is a constant and denoted by N_A

For example

One mole of sodium contain 6.02 x 10 ²³ atoms

One mole of carbon dioxide contain 6.02 x 10 ²³ molecules

One mole of hydroxyl Ion contains 6.02 x 10 ²³ ions

Molar volume

One mole of any gas at standard temperature and pressure occupies 22.414dm^-3.

For example

One mole of H₂ contains 6.02 x 10 ²³ molecules is equal to 22.414 dm³

STOICHIOMETRY

The branch of chemistry which deals with quantitative relations between reactants and products in a balanced chemical equation

Limitation of Balanced chemical equation

They do not tell about

· Conditions

· Rate of reaction

· Physical state of reactants and products

· Mechanism of reaction

Condition for stoichiometry calculation

· All reactants must be completely converted into products

· The side reaction must not occur

· The law of conservation of mass and law of Definite proportion must be obeyed while doing the calculations

Limiting Reactant

Limiting reactant is a reactant that controls the amount of product formed in a chemical reaction due to being less than the required amount

It can also be defined as follows

· It is a reactant that produce least number of moles of product

· It is consumed earlier in the reaction

Identification of Limiting Reactant

· Calculate the number of moles from the given amount of reactants

· Calculate the number of moles of product formed from the given moles of each reactant

· Identify the reactant as a limiting reactant which produces least moles of product

Yield

The amount of product obtained as a result of chemical reaction is called yield

Types of Yield:

Theoretical yield: The amount of product calculated from the balanced chemical equation is called theoretical yield

Actual yield: The amount of product obtained in a chemical reactions experimentally is called actual yield

Percentage yield: it is the ratio between actual yields divided by theoretical yield x 100

Note: actual yield is always less than theoretical yield

Isotopes

The atoms of same element having same atomic number but different atomic masses are called isotopes

For example: Hydrogen has three isotopes naming protium, deuterium and tritium respectively Carbon has three isotopes Chlorine has two isotopes Oxygen has three isotopes Nickel has five Calcium has six Palladium has six Cadmium has nine and Tin has 11 isotopes the majority of elements of the periodic table have some number of isotopes

Note: those elements which have only one isotopes are called monoisotopic elements

For example: gold, Arsenic, Iodine and Fluorine are mono isotopic elements

Isobars: Atoms of element having same atomic message but different atomic number. For example,

Calcium have mass number 40 and atomic number is 20 but argon has mass number 40 but atomic number is 18

Isotones: Atoms of element have same number of neutrons. For Example, Carbon-14, Oxygen-16 and Nitrogen-15 have same number of neutrons.

Relative Abundance of Isotopes:

The percentage of a particular isotope of element which exist naturally is called the relative abundance of isotopes

280 different isotopes are present naturally. They include 40 radioactive isotopes as well. About 300 isotopes are unstable radioactive produced through artificial disintegration of atoms of different element. Out of 280, 240 isotopes are stable. The relative abundance of isotopes can be determined by mass spectrometry

For example:

The elements like arsenic following iodine and gold have only a single isotope they are called monoisotopic substances.

In general the element of odd atomic number almost never possesses more than two stable isotopes the element of even atomic number usually have much larger number of isotopes. Oxygen magnesium silicon calcium iron farm nearly 50% of the earth crust out of 280 isotopes that occur in nature 154 are of even mass number and even atomic number and 126 has odd Match number and atomic number. Isotopes are separated from each other based upon their properties.

Mass spectrometry

The technique in which atoms or molecules are converted into ions are Separated on the basis of charge to mass ratio

Mass spectrometer: An instrument used to measure the exact mass of different isotopes of an atom of element with their relative abundance is called mass spectrometer

Types of mass spectrometer

· Aston mass spectrometer

· Dempster's Mass spectrometer

· Modern Mass spectrometer

Aston mass spectrometer: It was designed to identify isotopes of an element on the basis of atomic masses

Dempster’s spectrometer: It was design to identify isotopes of element which are in solid state

Parts of modern mass spectrometer

Vaporization chamber: In this chamber the sample of element is vaporized in this chamber the Vapors pressure is reduced to 10 ^-7 to 10^-6 Torr.

Ionization chamber: In this chamber sample of element is ionized either by alpha rays are by Electron beam

Electric field: Electric field is applied to accelerate the positive ions the applied potential Difference is of 500- 2000 volts.

Magnetic field: On passing through magnetic field deflection of positive ions takes place According to their mass to charge ratio.

Electrometer or ion collector: And collector receive positive ions according to their mass to Charge ratio related to isotopes

1) The strength of current measured by ions collector gives the relative abundance of isotopes of a definite mass to charge value

2) The same experiment is performed with carbon 12 isotopes and current strength is compared

Other techniques for the separation of isotopes

· Gas diffusion

· Thermal diffusion

· Distillation

· Ultracentrifugation

· Electromagnetic separation

· Laser separation

The mass spectrometer tells us

· The number of isotopes the number of peaks represents the number of isotopes of an atom of an element

· The abundance of isotopes the relative height of peaks give the direct measure of the relative abundance of isotopes

Fractional atomic mass

Atomic mass of elements depends upon the number of isotopes of an element and their natural abundance.

Combustion analysis

Those compounds which simply consists of carbon hydrogen and oxygen can be analyzed by very easily by combustion analysis. The product of combustion is H₂O and CO₂.these two products are collected separately and weighed.

The carbon and hydrogen present in the compound reacts with oxygen in the presence of cupric oxide and change into carbon dioxide and water respectively. These gases are passed first through water absorber containing magnesium dichlorate and then through carbon dioxide absorber which contains 50% potassium hydroxide solution.

The increase in mass of these absorbers corresponds to the main source of water and carbon dioxide produce in an organic compound. The percentage to Carbon and Hydrogen from the mass of carbon dioxide and water can be determined directly and mass of Oxygen which is in excess cannot be determined directly

Note: there are two methods through which nitrogen from organic compound can be estimated and following methods are

a) Dumas method

b) Kjeldahl method

Empirical Formula

The simplest whole number ratio of atoms of different elements in a compound is called empirical formula. For example, empirical formula of glucose C₆ H₁₂ O₆ is CH₂ O, empirical formula of hydrogen peroxide H₂O₂ is HO

The empirical and molecular formula of CH₄, NH_3, H₂O and C₁₂ H₂₂ O₁₁ are the same because they cannot be simplified. Ionic compounds have empirical formula but no molecular formula.

Molecular Formula

Actual number of atoms of different elements present in a molecule is called molecular formula.

For example benzene C₆ H₆, ethane C₂ H₆, Sodium Peroxide and Na₂ O₂, mercuric chloride and glucose have molecular formulas. In all these compounds the molecular formulas are simple multiple of empirical formulas, Hence.

Molecular formula= n x Empirical Formula

(Where n is the simple integer. those compounds whose empirical and Molecular formulas are same or numerous for example sodium chloride water carbon dioxide ammonia and sucrose have same empirical and Molecular formulas

Note: Empirical Formula of hemoglobin is C₇₅₉ H₁₂₀₈ N ₂₁₀ S₂ O₂₀₄ Fe