Kohlrausch Law directs the electrolyte’s limiting molar conductivity with its constituent ions. It displays that at infinite dilution equivalent conductivity of an electrolyte is equivalent to the sum of the conductances of the cations and anions. For example, the equivalent conductivity of CH3COONa at equivalent dilution would be equivalent to the sum of the conductances of the acetate and sodium ion.

Kohlrausch Law Questions – Practice Questions of Kohlrausch Law with Answer & Explanations

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Kohlrausch Law directs the electrolyte’s limiting molar conductivity with its constituent ions. It displays that at infinite dilution equivalent conductivity of an electrolyte is equivalent to the sum of the conductances of the cations and anions. For example, the equivalent conductivity of CH3COONa at equivalent dilution would be equivalent to the sum of the conductances of the acetate and sodium ion.

𝛬mº CH3COONa = 𝛬mº CH3COO – + 𝛬mº Na +

Definition: Kohlrausch’s law states that the equivalent conductivity of an electrolyte at infinite dilution is equivalent to the sum of the conductances of cations and anions.

Kohlrausch Law Chemistry Questions with Solutions

Q1. Equivalent conductance of a strong electrolyte increases on dilution due to

(a) An increase in the number of ions and the ionic mobility of solution

(b) Complete dilution of the electrolyte at standard dilution

(c ) An increase in the ionic mobility of solution

(d) None of the above

Answer: (c ) Equivalent conductance of a strong electrolyte increases on dilution due to an increase in the ionic mobility of solution.

Q2. The molar conductivity of an ionic solution depends on

(a) Concentration of electrolytes in solution

(b) Distance between electrodes

(c ) Surface area of electrodes

(d) None of the above

Answer: (a) The molar conductivity of an ionic solution depends on the concentration of electrolytes in solution.

Q3. The molar conductance of a solution ___________ with dilution while its specific conductance ________ with dilution.

(a) Decreases, Increases

(b) Increases, Decreases

(c ) Decreases, Decreases

(d) Increases, Increases

Answer: (a) The molar conductance of a solution increases with dilution while its specific conductance decreases with dilution.

Q4. Kohlrausch’s law states that at

(a) Infinite dilution, the equivalent conductivity of an electrolyte is equivalent to the sum of the conductances of the cations and anions

(b) Finite dilution, the equivalent conductivity of an electrolyte is equivalent to the sum of the conductances of the cations and anions.

(c ) Both (a) and (b)

(d) None of the above

Answer: (a) Kohlrausch’s law states that at infinite dilution, the equivalent conductivity of an electrolyte is equivalent to the sum of the conductances of the cations and the anions

Q5. Which of the following statements is correct for an electrolytic solution upon dilution?

(a) Conductivity increase on dilution

(b) Conductivity decrease on dilution

(c ) Molar conductance decreases, but equivalent conductance increases on dilution

(d) Molar conductance increases, but equivalent conductance decreases on dilution

Answer: (b) When an electrolytic solution is diluted, it’s concentration decreases. Due to this, the conductance increases, and the conductivity decreases.

Q6. What is Kohlrausch’s law?

Answer: Kohlrausch’s law states that at infinite dilution equivalent conductivity of an electrolyte is equivalent to the sum of the conductances of the cations and anions.

Q7. What are the applications of Kohlrausch’s law?

Answer: Kohlrausch’s law states that at infinite dilution equivalent conductivity of an electrolyte is equivalent to the sum of the conductances of the cations and anions. There are a lot of applications of Kohlrausch’s law.

A few of them are mentioned below.

1. It can be used to calculate the molar conductance at infinite dilution for a weak electrolyte.

2. It can be used to calculate the degree of dissociation at infinite dilution for a weak electrolyte.

3. It can be used to calculate the dissociation constant at infinite dilution for a weak electrolyte.

4. It can be used to calculate the solubility of the sparingly soluble salt.

Q8. The 𝛬mº for sodium iodide, sodium acetate, and magnesium acetate solution are 12.69, 9.10 and 18.78 S cm2 mol-1, respectively, at 298 K. Calculate 𝛬mº for magnesium iodide.

Answer:

We know that

𝛬mº (NaI) = 12.69 S cm2 mol-1

𝛬mº (CH3COONa) = 9.10 S cm2 mol-1

𝛬mº (MgI2) = 18.78 S cm2 mol-1

According to Kohlrausch’s law

𝛬mº (MgI2) = 𝛬mº [CH3(COO)]2Mg + 2 𝛬mº (NaI) – 2 𝛬mº (CH3COONa)

𝛬mº (MgI2) = (18.78 + 2 X 12.69 – 2 X 9.10) S cm2 mol-1

𝛬mº (MgI2) = (18.78 + 25.38 – 18.20) S cm2 mol-1

𝛬mº (MgI2) = (44.16 – 18.20) S cm2 mol-1

𝛬mº (MgI2) = 25.96 S cm2 mol-1

Q9. Calculate 𝛬mº for CaCl2 and MgSO4 from the following data:

𝛬mº (Ca2+) = 119.0 S cm2 mol-1, 𝛬mº (Mg2+) = 106.0 S cm2 mol-1, 𝛬mº (Cl–) = 76.3 S cm2 mol-1 and 𝛬mº (SO42- ) = 160.05 S cm2 mol-1

Answer:

We know that,

𝛬mº (Ca2+) = 119.0 S cm2 mol-1

𝛬mº (Mg2+) = 106.0 S cm2 mol-1

𝛬mº (Cl–) = 76.3 S cm2 mol-1

𝛬mº (SO42- ) = 160.05 S cm2 mol-1

According to Kohlrausch’s law

𝛬mº (CaCl2) = 𝛬mº (Ca2+) + 2 X [𝛬mº (Cl–)]

𝛬mº (CaCl2) = [119.0 + 2 X 76.3] S cm2 mol-1

𝛬mº (CaCl2) = [119.0 + 152.6] S cm2 mol-1

𝛬mº (CaCl2) = 271.6 S cm2 mol-1

And

𝛬mº (MgSO4) = 𝛬mº (Mg2+) + 𝛬mº (SO42- )

𝛬mº (MgSO4) = [106.0 + 160.05] S cm2 mol-1

𝛬mº (MgSO4) = 266.05 S cm2 mol-1

Q10. The 𝛬mº for sodium acetate, HCl, and NaCl are 91.0, 425.9 and 126.4 S cm2 mol-1, respectively, at 298 K. Calculate 𝛬mº for CH3COOH.

Answer:

We know that,

𝛬mº (CH3COONa) = 91.0 S cm2 mol-1

𝛬mº (HCl) = 425.9 S cm2 mol-1

𝛬mº (NaCl) = 126.4 S cm2 mol-1

According to Kohlrausch’s law

𝛬mº CH3COOH = 𝛬mº CH3COONa + 𝛬mº HCl – 𝛬mº NaCl

𝛬mº CH3COOH = (91.0 + 425.9 – 126.4) S cm2 mol-1

𝛬mº CH3COOH = 390.5 S cm2 mol-1

Q11. The molar conductivity of a 1.5 M solution of an electrolyte is found to be 138.9 S cm2 mol −1. Calculate the conductivity of this solution.

Answer: Molar conductivity (𝜆m) = 138.9 S cm2 mol −1

Concentration = 1.5 M

Molar conductivity = Conductivity / Concentration

Conductivity = Molar conductivity X Concentration

Conductivity = (138.9 S cm2 mol −1 X 1.5 M) / 1000 cm3 L-1

Conductivity = 0.208 S cm -1

Q12. The resistance and conductivity of a cell containing 0.001 M KCl solution at 298 K are 1500 Ω and 1.46 X 10−4 S cm−1, respectively. What is the cell constant of the cell?

Answer:

Resistance = 1500 Ω

Conductivity = 1.46 X 10−4 S cm−1

Concentration = 0.001 M

Temperature = 298 K

We know that,

Conductivity = Cell constant / Resistance

1.46 X 10−4 S cm−1 = Cell constant / 1500 Ω

Cell constant = 1.46 X 10−4 S cm−1 X 1500 Ω

Cell constant = 0.219 cm -1

Q13. The conductivity of the 0.20 M solution of KCl at 298 K is 0.0248 S cm−1. Calculate its molar conductivity.

Answer:

Conductivity = 0.0248 S cm−1

Concentration = 0.20 M

Temperature = 298 K

Molar conductivity (𝜆m) = (Conductivity X 1000) / C

Molar conductivity (𝜆m) = (0.0248 S cm−1 X 1000) / 0.20 mol cm -3

Molar conductivity (𝜆m) = 24.8 S cm−1 / 0.20 mol cm -3

Molar conductivity (𝜆m) = 124 S cm2 mol−1

Q14. The molar conductivity of NaCl, HCl and CH3COONa at infinite dilution are 126.45, 426.16 and 91 S cm2 mol −1, respectively. What will be the molar conductivity of CH3COOH at infinite dilution?

Answer:

We know that,

𝛬mº (NaCl) = 126.45 S cm2 mol −1

𝛬mº (HCl) = 426.16 S cm2 mol −1

𝛬mº (CH3COONa) = 91 S cm2 mol −1

According to Kohlrausch’s law

𝛬mº CH3COOH = 𝛬mº CH3COONa + 𝛬mº HCl – 𝛬mº NaCl

𝛬mº CH3COOH = (91 + 426.16 – 126.45) S cm2 mol −1

𝛬mº CH3COOH = (91 + 426.16 – 126.45) S cm2 mol −1

𝛬mº CH3COOH = (517.16 – 126.45) S cm2 mol −1

𝛬mº CH3COOH = 390.71 S cm2 mol −1

Q15. Match the following.

Column AColumn B
Kohlrausch’s lawK α = Cα2 / 1 – α
Molar conductivityα = Λ m / Λ m o
Degree of dissociationΛ m = k / C
Dissociation constantΛ eq o = Λ c o + Λ a o

Answer:

Column AColumn B
Kohlrausch’s lawΛ eq o = Λ c o + Λ a o
Molar conductivityΛ m = k / C
Degree of dissociationα = Λ m / Λ m o
Dissociation constantK α = Cα2 / 1 – α

Practise Questions on Kohlrausch Law

Q1. Why can 𝛬mº for CH3COOH not be determined experimentally?

Q2. Why does the conductivity of a solution decrease with dilution?

Q3. The conductivity of 0.00241 M acetic acid is 7.896 X 10-5 S cm-1. Calculate its molar conductivity, and if 𝛬mº for acetic acid is 390.5 S cm2 mol -1, what is its dissociation constant?

Q4. Three electrolytic cells A, B, and C, containing a solution of ZnSO4, AgNO3 and CuSO4, respectively all connected in series. A steady current of 1.5 amperes was passed through then until 1.45 g of silver was deposited at the cathode of cell B. How long did the current flow? What mass of copper and zinc were deposited?

Q5. Suggest a way to determine the 𝛬mº of CH3COOH.

Er. Neeraj K.Anand is a freelance mentor and writer who specializes in Engineering & Science subjects. Neeraj Anand received a B.Tech degree in Electronics and Communication Engineering from N.I.T Warangal & M.Tech Post Graduation from IETE, New Delhi. He has over 30 years of teaching experience and serves as the Head of Department of ANAND CLASSES. He concentrated all his energy and experiences in academics and subsequently grew up as one of the best mentors in the country for students aspiring for success in competitive examinations. In parallel, he started a Technical Publication "ANAND TECHNICAL PUBLISHERS" in 2002 and Educational Newspaper "NATIONAL EDUCATION NEWS" in 2014 at Jalandhar. Now he is a Director of leading publication "ANAND TECHNICAL PUBLISHERS", "ANAND CLASSES" and "NATIONAL EDUCATION NEWS". He has published more than hundred books in the field of Physics, Mathematics, Computers and Information Technology. Besides this he has written many books to help students prepare for IIT-JEE and AIPMT entrance exams. He is an executive member of the IEEE (Institute of Electrical & Electronics Engineers. USA) and honorary member of many Indian scientific societies such as Institution of Electronics & Telecommunication Engineers, Aeronautical Society of India, Bioinformatics Institute of India, Institution of Engineers. He has got award from American Biographical Institute Board of International Research in the year 2005.

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CBSE Class 12 Chemistry Syllabus Download PDF

Below is the CBSE Class 12 Syllabus along with the marking scheme and time duration of the Chemistry exam.

S.NoTitleNo. of PeriodsMarks
1Solutions107
2Electrochemistry129
3Chemical Kinetics107
4d -and f -Block Elements127
5Coordination Compounds127
6Haloalkanes and Haloarenes106
7Alcohols, Phenols and Ethers106
8Aldehydes, Ketones and Carboxylic Acids108
9Amines106
10Biomolecules127
Total70

CBSE Class 12 Chemistry Practical Syllabus along with Marking Scheme

The following is a breakdown of the marks for practical, project work, class records, and viva. The total number of marks for all parts is 15. The marks for both terms are provided in the table below.

Evaluation Scheme for ExaminationMarks
Volumetric Analysis08
Salt Analysis08
Content-Based Experiment06
Project Work and Viva04
Class record and Viva04
Total30

CBSE Class 12 Chemistry Syllabus (Chapter-wise)

Unit -1: Solutions

  • Raoult's law.
  • Colligative properties - relative lowering of vapour pressure, elevation of boiling point, depression of freezing point, osmotic pressure, determination of molecular masses using colligative properties, abnormal molecular mass.
  • Solutions, Types of solutions, expression of concentration of solutions of solids in liquids, solubility of gases in liquids, solid solutions.
  • Van't Hoff factor.

Unit -2: Electrochemistry

  • Redox reactions, EMF of a cell, standard electrode potential
  • Nernst equation and its application to chemical cells
  • Relation between Gibbs energy change and EMF of a cell
  • Kohlrausch's Law
  • Electrolysis and law of electrolysis (elementary idea)
  • Dry cell-electrolytic cells and Galvanic cells
  • Conductance in electrolytic solutions, specific and molar conductivity, variations of conductivity with concentration.
  • Lead accumulator
  • Fuel cells

Unit -3: Chemical Kinetics

  • Rate of a reaction (Average and instantaneous)
  • Rate law and specific rate constant
  • Integrated rate equations and half-life (only for zerfirst-order order reactions)
  • Concept of collision theory (elementary idea, no mathematical treatment)
  • Factors affecting rate of reaction: concentration, temperature, catalyst;
  • Order and molecularity of a reaction
  • Activation energy
  • Arrhenius equation

Unit -4: d and f Block Elements  

  • Lanthanoids- Electronic configuration, oxidation states, chemical reactivity and lanthanoid contraction and its consequences.
  • Actinoids- Electronic configuration, oxidation states and comparison with lanthanoids.
  • General introduction, electronic configuration, occurrence and characteristics of transition metals, general trends in properties of the first-row transition metals – metallic character, ionization enthalpy, oxidation states, ionic radii, color, catalytic property, magnetic properties, interstitial compounds, alloy formation, preparation and properties of K2Cr2O7 and KMnO4.

Unit -5: Coordination Compounds  

  • Coordination compounds - Introduction, ligands, coordination number, color, magnetic properties and shapes
  • The importance of coordination compounds (in qualitative analysis, extraction of metals and biological system).
  • IUPAC nomenclature of mononuclear coordination compounds.
  • Bonding
  • Werner's theory, VBT, and CFT; structure and stereoisomerism

Unit -6: Haloalkanes and Haloarenes  

  • Haloarenes: Nature of C–X bond, substitution reactions (Directive influence of halogen in monosubstituted compounds only). Uses and environmental effects of - dichloromethane, trichloro methane, tetrachloromethane, iodoform, freons, DDT.
  • Haloalkanes: Nomenclature, nature of C–X bond, physical and chemical properties, optical rotation mechanism of substitution reactions.

Unit -7: Alcohols, Phenols and Ethers   

  • Phenols: Nomenclature, methods of preparation, physical and chemical properties, acidic nature of phenol, electrophilic substitution reactions, uses of phenols.
  • Ethers: Nomenclature, methods of preparation, physical and chemical properties, uses.
  • Alcohols: Nomenclature, methods of preparation, physical and chemical properties (of primary alcohols only), identification of primary, secondary and tertiary alcohols, mechanism of dehydration, and uses with special reference to methanol and ethanol.

Unit -8: Aldehydes, Ketones and Carboxylic Acids   

  • Carboxylic Acids: Nomenclature, acidic nature, methods of preparation, physical and chemical properties; uses.
  • Aldehydes and Ketones: Nomenclature, nature of carbonyl group, methods of preparation, physical and chemical properties, mechanism of nucleophilic addition, the reactivity of alpha hydrogen in aldehydes, uses.

Unit -9: Amines    

  • Diazonium salts: Preparation, chemical reactions and importance in synthetic organic chemistry.
  • Amines: Nomenclature, classification, structure, methods of preparation, physical and chemical properties, uses, and identification of primary, secondary and tertiary amines.

Unit -10: Biomolecules     

  • Proteins -Elementary idea of - amino acids, peptide bond, polypeptides, proteins, structure of proteins - primary, secondary, tertiary structure and quaternary structures (qualitative idea only), denaturation of proteins; enzymes. Hormones - Elementary idea excluding structure.
  • Vitamins - Classification and functions.
  • Carbohydrates - Classification (aldoses and ketoses), monosaccharides (glucose and fructose), D-L configuration oligosaccharides (sucrose, lactose, maltose), polysaccharides (starch, cellulose, glycogen); Importance of carbohydrates.
  • Nucleic Acids: DNA and RNA.

The syllabus is divided into three parts: Part A, Part B, and Part C. Part A consist of Basic Concepts of Chemistry, which covers topics such as atomic structure, chemical bonding, states of matter, and thermochemistry. Part B consists of Topics in Physical Chemistry, which includes topics such as chemical kinetics, equilibrium, and electrochemistry. Part C consists of Topics in Organic Chemistry, which covers topics such as alkanes, alkenes, alkynes, and aromatic compounds.

Basic Concepts of Chemistry:

  • Atomic structure: This section covers the fundamental concepts of atomic structure, including the electronic configuration of atoms, the Bohr model of the atom, and the wave nature of matter.
  • Chemical bonding: This section covers the different types of chemical bonds, including ionic, covalent, and metallic bonds, as well as the concept of hybridization.
  • States of the matter: This section covers the three states of matter - solid, liquid, and gas - and the factors that influence their properties.
  • Thermochemistry: This section covers the principles of thermochemistry, including the laws of thermodynamics and the concept of enthalpy.

Chapters in Physical Chemistry:

  • Chemical kinetics: This section covers the study of the rate of chemical reactions and the factors that influence it, including the concentration of reactants, temperature, and the presence of catalysts.
  • Equilibrium: This section covers the principles of chemical equilibrium, including the concept of Le Chatelier's principle and the equilibrium constant.
  • Electrochemistry: This section covers the principles of electrochemistry, including the concept of half-cell reactions, galvanic cells, and electrolysis.

Chapters in Organic Chemistry:

  • Alkanes: This section covers the properties and reactions of alkanes, including their structure, isomerism, and combustion.
  • Alkenes: This section covers the properties and reactions of alkenes, including their structure, isomerism, and addition reactions.
  • Alkynes: This section covers the properties and reactions of alkynes, including their structure, isomerism, and addition reactions.
  • Aromatic compounds: This section covers the properties and reactions of aromatic compounds, including their structure, isomerism, and electrophilic substitution reactions.

In addition to the topics covered in the syllabus, the CBSE Class 12 Chemistry exam also tests students on their analytical and problem-solving skills, as well as their ability to apply the concepts learned in the classroom to real-world situations.

Students can also check out the Tips for the Class 12 Chemistry Exam. They can easily access the Class 12 study material in one place by visiting the CBSE Class 12 page at ANAND CLASSES (A School Of Competitions). Moreover, to get interactive lessons and study videos, download the ANAND CLASSES (A School Of Competitions) App.

Frequently Asked Questions on CBSE Class 12 Chemistry Syllabus

Q1

How many chapters are there in the CBSE Class 12 Chemistry as per the syllabus?

There are 10 chapters in the CBSE Class 12 Chemistry as per Syllabus. Students can learn all these chapters efficiently using the study materials provided at ANAND CLASSES (A School Of Competitions).

Q2

What is the marking scheme for CBSE Class 12 Chemistry practical exam according to the syllabus?

The marking scheme for CBSE Class 12 Chemistry practical exam, according to the syllabus, is 8 marks for volumetric analysis, 8 marks for salt analysis, 6 marks for the content-based experiment, 4 marks for the project and viva and 4 marks for class record and viva.

Q3

Which is the scoring chapter in Chemistry as per CBSE Class 12 syllabus?

The chapter Electrochemistry in Chemistry is the scoring chapter as per CBSE Class 12 syllabus.

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