Equivalent and Molar Conductance, Kohlrausch’s Law, Factors Affecting Equivalent Conductivity, Solved Examples

Equivalent Conductance

We can state that an electrolytic solution’s conductance is influenced by the ion concentration present in the solution. Having comparable outcomes for various electrolytes is beneficial. It’s represented by the symbol ∧e. From specific conductance, equivalent conductance is computed.

Unit of Equivalent Conductance is ohm-1cm2eq-1.

Equivalent Conductance Formula is as follows:

e = K × V

Where,

  • e = Equivalent Conductance,
  • K = Specific Conductance (Reciprocal of Specific Resistance),
  • V = Volume (in ml) of 1 gm-equivalent electrolyte.

Also,

e = (K × 1000) / N

Where,

N = Normality

Derivation of Equivalent Conductance

Conductance of V cm3 = ∧e

Conductance of 1 cm3 = K

Therefore, ∧e = K × V  …(Equation 1)

We are aware that the equation below provides information about a solution’s normality (N).

N = (n/V) × 1000

∴ V = (1000 × n) / N

Number of equivalents, n = 1, for the electrolytic solution mentioned above.

V = 1000 / N

Substitute value of V in Equation 1,

∴ ∧e = (K × 1000) / N

Conductors and Insulators

Conductors are substances that make it simple and unhindered for electrons to go from one end to the other. Conductors contain electric charges in the form of electrons, which facilitates the electrons’ free movement.

On the other hand, insulators are the kind of substances that obstruct the easy movement of electrons from one end to other. Any charge that is transferred through an insulator only settles at the point where the two materials first come together; it does not expand outward.

Equivalent conductance at infinite dilution

The value of equivalent conductance rises as the solution becomes more diluted as ionization, or the amount of ions in a solution, rises. However, there comes a point where further dilution of the solutions is impossible, meaning it has no impact whatsoever on the solution’s concentration. The infinite dilution is the name given to the entire idea when diluting ceases.

Since a solution already has the maximum amount of solvent that may be added, infinite dilution is the condition in which no further concentration can be achieved with any amount of dilution. In this infinite dilution condition, all ions are fully dissociated.

Kohlrausch’s Law

According to Kohlrausch’s law, each ion contributes significantly to the equivalent conductance of the electrolyte at infinite dilution when dissociation is complete, regardless of the type of ion it is associated with. The value of equivalent conductance at infinite dilution for any electrolyte is the sum of the contributions of its constituent ions (cations and anions). We can therefore interpret it to mean that “conductivity of an electrolyte’s ions at infinite dilution is constant and does not depend on the nature of co-ions.”

λeq = λc + λa

Where,

  • λeq = Molar conductivity at infinity of dilution,
  • λc = Conductivity of cation at infinity of dilution,
  • λa = Conductivity of anion at infinity of dilution.

The term “limiting molar conductivity” refers to the molar conductivity that exists when the electrolyte concentration is almost zero.

When held between two electrodes with a unit area of cross-section and a unit distance, the volume of the solution that conducts and also contains one mole of electrolyte is known as the molar conductivity. Molar conductivity rises as concentration falls. The volume that makes up one mole of electrolytes increases, which results in an increase in the molar conductivity. When the electrolyte concentration becomes close to zero, the molar conductivity is known as the limiting molar conductivity.

Uses of Kohlrausch’s Law

  1. The molar conductivity at infinite dilution for the weak electrolytes is determined using Kohlrausch’s law. Calculating the molar conductivity of weak electrolytes at infinite dilution is highly challenging or impossible. due to the extremely low conductance of these sorts of solutions and the fact that the dissociation of these electrolytes is incomplete even at high dilutions.
  2. The solubility of a moderately soluble salt is determined using Kohlrausch’s law. Some salts are referred to as weakly or sparingly soluble salts because they only slightly dissolve in water. For instance, silver chloride, lead sulfate, barium sulfate, etc.
  3. The term “limiting molar conductivity” refers to the molar conductivity that exists when the electrolyte concentration is almost zero. We can calculate the limiting molar conductivity of an electrolyte using Kohlrausch’s law.

Molar Conductivity

Molar conductivity, which can be determined by a solution’s ionic strength or salt concentration, is the conductance of a solution containing one mole of electrolyte. It is therefore not a constant. 

Molar conductivity, then, is the sum of the conductivities of all the ions produced when a mole of an electrolyte is dissolved in a solution. The ability of an electrolyte to transmit electricity in a solution is generally assessed using the property of an electrolyte solution called molar conductivity. It is therefore not a constant. The unit of Molar conductivity is Sm2mol-1.

The following expression is used to numerically represent molar conductivity:

μ = K/C

Where,

  • K = Specific Conductivity,
  • C = the concentration of moles per liter.

Factors Affecting Equivalent Conductivity

  • Temperature: As temperature rises, more ions are produced, which results in an increase in an electrolyte solution’s conductance.
  • Strong electrolytes completely ionize, producing more ions as a result of which they have higher conductivities.
  • On the other hand, weak electrolytes only experience partial ionization, which results in low conductivity in their solutions.
  • Ionic size and mobility: As an ion’s size grows, so does its mobility, and its conductivity also decreases.
  • Because of the solvent’s composition and viscosity, ionic mobility is reduced in more viscous solvents. The conductivity consequently declines.

Solved Examples

Question 1: What Does Equivalent Conductance Mean in Chemistry?

Answer:

Equivalent conductance of an electrolyte is defined as the conductance of a volume of solution containing one equivalent weight of dissolved substance when placed between two parallel electrodes spaced 1 cm apart and big enough to hold the entire solution between them.

Question 2: Write Two Factors Affecting Equivalent Conductivity.

Answer:

Factors Affecting Equivalent Conductivity:

  1. Strong electrolytes fully ionize, resulting in the production of more ions and higher conductivities.
  2. Ionic size and mobility: An ion’s mobility increases with its size while its conductivity decreases.

Question 3: List the situations in which the independent ion migration law of Kohlrausch is applicable.

Answer:

For weak electrolytes, it is used to determine the limiting molar conductivity, level of dissociation, and dissociation constant. It is also employed in the computation of the salt’s solubility.

Sample Problems

Problems 1: A 0.7 N salt solution put between two platinum electrodes separated by 2 cm and covering an area of 6 cm2 has a 25-ohm resistance. calculate equivalent conductivity.

Solution:

Since,

e = (K × 1000) / N

∴ ∧e = 1/25 × 2/6 × 1000/0.7

∴ ∧e = 0.04 × 0.33 × 1428.5

∴ ∧e = 18.8562 ohm-1cm2eq-1

Problems 2: A salt solution in N/10 is found to have a resistance of 1.2 × 103 ohms. Calculate the solution’s equivalent conductance. 1.5 cm-1 is the cell constant.

Solution:

Since,

e = (K × 1000) / N

K = cell constant × conductance

∴ K = 1.5 × (1/1.2 × 103)

∴ K = 1.25 × 10-3

e = K × 1000 / N

∴ ∧e = 1.25 × 10-3 / (1/10)

∴ ∧e = 1.25 × 10-3 / 0.1

∴ ∧e = 12.5 × 10-3 ohm-1cm2eq-1

Problems 3: Calculate the volume of the solution if the equivalent conductance is 10.255 ohm-1cm2eq-1 and the specific conductance is 2.17 cm-1ohms-1.

Solution:

Since,

e = K × V

∴ V = ∧e / K

∴ V = 10.255 / 2.17

∴ V = 4.7258 cm3

Problems 4: Calculate the Equivalent conductance if the specific conductance is 1.83 cm-1ohms-1 and the volume of the solution is 3.91 ml.

Solution:

Since,

e = K × V

∴ ∧e = 1.83 × 3.91

∴ ∧e = 7.1553 ohm-1cm2eq-1

Problems 5: It is discovered that a salt solution in N/100 has a resistance of 5.21 × 103 ohms. Calculate the equivalent conductance of the solution. The cell constant is 3.71 cm-1.

Solution:

Since,

e = (K × 1000) / N

K = cell constant × conductance

∴ K = 3.71 × (1/5.21 × 103)

∴ K = 0.7120 × 10-3

e = K × 1000 / N

∴ ∧e = 0.7120 × 10-3 / (1/100)

∴ ∧e = 0.7120 × 10-3 / 0.01

∴ ∧e = 71.2 × 10-3 ohm-1cm2eq-1

Problems 6: Calculate the Equivalent conductance if the specific conductance is 3.11 cm-1ohms-1 and the volume of the solution is 2.95 ml.

Solution:

Since,

e = K × V

∴ ∧e = 3.11 × 2.95

∴ ∧e = 9.1745 ohm-1cm2eq-1

Problems 7: If the equivalent conductance is 2.916 × 103 ohm-1cm2eq-1 and the specific conductance is 2.87 cm-1ohms-1 then calculate the volume of the solution.

Solution:

Since,

e = K × V

∴ V = ∧e / K

∴ V = 2.916 × 103 / 2.87

∴ V = 1.0160 × 103 cm3

Problems 8: Calculate λm for Cacl2 if λCa2+ = 137.0 Scm2mol-1 and λcl = 65.9 Scm2mol-1.

Solution:

Since,

λom Cacl2 = λo Ca2+ + 2λocl

∴ λom Cacl2 = 137 + (2 × 65.9)

∴ λom Cacl2 = 137 + 131.8

∴ λom Cacl2 = 268.8 Scm2mol-1

Problems 9: Calculate λom for MgSO4 if λoMg2+ = 119 Scm2mol-1 and λoSO42- = 241 Scm2mol-1.

Solution:

Since,

λom MgSO4 = λo Mg2+ + λo SO42-

∴ λom MgSO4 = 119 + 241

∴ λom MgSO4 = 360 Scm2mol-1

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.

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.