CBSE Important Questions Class 12 Chemistry Chapter 3

Important Questions Class 12 Chemistry Chapter 3

Important Questions For CBSE Class 12 Chemistry Chapter 3 – Electrochemistry

Electrochemistry is a branch of chemistry that deals with the study of the relationship between electrical energy and chemical changes. Electrochemistry is used extensively in the battery industry, electrical appliances and other technological applications. 

The concept of Electrochemistry is covered in Chapter 3 of Class 12 Chemistry. Besides having vast applications in various fields, this chapter is important from the exam perspective as well. Therefore, students must know which concepts are important and what kind of numerical problems they must practise scoring more in the board exam.

At Extramarks, Important Questions Class 12 Chemistry Chapter 3 are prepared by subject matter experts after a thorough analysis of the question papers of the past years. This set of questions will help students practise more questions before the exam to give an edge to their preparation.

CBSE Class 12 Chemistry Chapter-3 Important Questions 
Study Important Questions For Class 12 Chemistry Chapter 3 – Electrochemistry

Below are a few examples of 1 mark, 2 marks, 3 marks and 5 marks questions. Access the link provided to review the full set of questions. 

Very Short Answer Questions 1 Mark

Q.1. What is molar conductivity?

Ans. The molar conductivity of a solution can be defined as the conducting power of all the ions produced by dissolving one mole of electrolyte in the solution.

Q2.  What is the relationship between molar conductivity and temperature?

Ans. The molar conductivity of an electrolyte increases with an increase in temperature.

Q.3. What is the emf of a cell?

Ans. The electromotive force or emf of a cell refers to the maximum potential difference between the two electrodes of a cell.

Q.4. When does the emf of a cell become zero?

Ans.  When the cell reaction attains the stage of equilibrium, the emf of the cell becomes zero.

Q.5. What is used in a dry cell as an electrolyte?

Ans. A paste of NH4Cl, MnO2 and Carbon is used as an electrolyte in a dry cell.

Q.6. What is an electrochemical series?

Ans. An electrochemical series is a special arrangement of electrodes in increasing and decreasing order based on their standard reduction potential.

Q.7. Construct the Nernst equation for the general cell reaction aA + bB → cC + dD.

Ans. The Nernst equation for the given general cell equation is as follows:

Ecell = E0 cell – RT ln Cc Dd nF Aa Bb .

Q.8. How is cell constant calculated from specific conductance and observed conductance?

Ans. The formula for calculating the cell constant is:

Cell constant = specific conductanceobserved conductance

Q.9. Which metal is used in a hydrogen electrode? What is the purpose of using it?

Ans. Platinum foils are used in hydrogen electrodes. It is used to maintain the inflow and outflow of electrons in a hydrogen electrode.

Q.10. What is the reason that in concentrated solutions, strong electrolytes deviate from the Debye-Huckel-Onsager equation?

Ans. Strong electrolytes in concentrated solutions deviate from the Debye-Huckel-Onsager equation due to the large interionic forces of attraction.

Q.11. Corrosion of motor cars is a common problem in winter when salt is spread on roads to melt the snow. Give a reason.

Ans. When two metals are brought together under the surface of an electrolyte, a short-circuited cell is formed. Motor cars contain metals like lead, chromium and salt (NaCl) sprinkled over ice that acts as an electrolyte. Thus, a short-circuited cell is formed when cars move on the salt spread on the ice. So, corrosion on cars becomes a great problem in winter.

Q.14. What is the purpose of using salt bridges in galvanic cells?

Ans. Salt bridges are used in galvanic cells to complete the inner circuit and to maintain the electrical neutrality of the solution.

Q.15. What is the significance of the internal circuit in a galvanic cell?

Ans. Ions flow in the internal circuit of a galvanic cell.

Short Answer Questions
2 Marks

Q.1. Electrolysis of KBr solution gives Br2 ions at the anode, but the solution of KF does not produce any F2 ions. Give a reason.

Ans. We get the negative ions at the anode because it is the electrode where oxidation takes place. The oxidation process becomes easy if the oxidation potential of the solution is high. Br- has the highest oxidation potential, followed by H2O, and finally F.

So, in the aqueous solution of KBr, Br ions are oxidised to Br2 in preference to H2O. On the other hand, in the aqueous solution of KF, H2O is oxidised in preference to F. Hence, in this case, oxidation of H2O at the anode gives O2 and thus no F2 is produced at the anode.

Q.2. What is corrosion?

Ans. Corrosion can be defined as the process of deterioration of metals because of their reaction with air and water. In this process, sulphides, oxides, carbonates, hydroxides, etc. are produced that slowly damage the metals. Rusting of iron is an example of corrosion. Rust is nothing but an oxide of iron (Fe2O3, x H2O).

Q.3. Describe the oxidation and reduction potential.

Ans. The oxidation potential of a chemical element refers to its propensity to be oxidised by losing one or more electrons at an electrode. Reduction potential, on the other hand, refers to the tendency of a chemical element to be reduced at the electrode by gaining one or more electrons.

Q.4. What is a cell constant? How do you determine it?

Ans. Cell constant can be defined as the ratio of the distance between the electrodes of a conductivity cell to their surface area. It can be determined by calculating the resistance of a cell of known conductivity.

Q.5. Why should we use mercury cells?

Ans. In a mercury cell, the overall cell reaction does not include any ions from the solution. So, the concentration of the solution remains constant. As a result, mercury cells give a constant voltage. Therefore, mercury cells are more advantageous.

Q.6. What do you understand about normal hydrogen electrodes? Why is it important?

Ans. Standard Hydrogen Electrode or better known as the normal hydrogen electrode is used as a reference for half-cell potential reactions.

By using a hydrogen electrode, it is possible to calculate cell potentials using different electrodes. This is also a standard measurement of electrode potential for the thermodynamic scale of redox potential.

Q.7. Write the equation that shows the effect of concentration on the electrode potential.

Ans. The equation that shows the effect of concentration on electrode potential is known as the Nernst Equation. It can be written as follows:

Ecell = Ecell −  RTnF1n Q


Ecell = the reduction potential at current potential

E⁰cell = the standard reduction potential relative to the reduction potential of hydrogen at 25⁰C

R = universal gas constant 

T =temperature in K

n = the moles of electrons transferred between the positive and negative terminals of an electrochemical system.

F =Faraday’s Constant

Q = reaction quotient

Q.8. What is the significance of the Nernst equation in the calculation of the equilibrium constant of any cell reaction? 

Ans:  Nernst equation, Ecell = Ecell −  RTnF1n Q

When the cell reaction reaches the equilibrium stage, then Q = Kc

Where Kc is the equilibrium constant

Therefore, from the Nernst Equation we get,

Ecell = Ecell −  RTnF1n Kc .

Q.9. A cell reaction is considered spontaneous if the overall emf of the cell is positive. Comment.

Ans. When the emf of a cell is positive, then the Gibbs free energy of the overall reaction is less than zero.

∆G = -nFEcell

Hence, the cell reaction is considered spontaneous.

Q.10. Write three differences between potential difference and emf.

Ans. Potential difference is the difference of potential of electrodes when there is a flow of electricity in the circuit; whereas emf refers to the electrode potential of two electrodes when there is no flow of electricity in the circuit.

The value of the potential difference is less than the maximum voltage obtained from the cell. Emf, on the other hand, is the maximum voltage obtained from a cell.

Potential difference is not responsible for a steady flow of current. Emf is responsible for the steady flow of the current in a circuit.

Long Answer Questions
5 Marks

Q.1 What is meant by “electrolytic conductance”? Name the factors that determine electrolytic conduction. What is the effect of temperature on it?

Ans. The ability of the electrolytic solutions to let the electric current pass through them is called electrolytic conductance.

The factors on which electrolytic conductance depends are as follows:

  1. Temperature
  2. The concentration of ions in the solution
  3. Nature of the electrolyte

The ability of electrolytes to get dissolved in a solution changes with the change in temperature. When temperature increases, the solubility also increases, and hence, the electrolytic conductance also increases.

Q.2. How is electrolytic conductance measured? 

Ans: The resistance between two nodes helps determine the conductance of electrolytes. When electricity passes through the solution, it produces positive ions and negative ions in the solution. The conductance of electrolytes can be measured by using galvanic cells or the method of electrolysis.

Q.3. Iron does not rust even if a zinc coating is broken in a galvanised iron pipe, but rusting occurs much faster if the tin coating over iron is broken. Why?

Ans: Iron is less electropositive than zinc. So, the coating of zinc on the surface of the iron pipe acts as an anode and the iron pipe itself acts as a cathode. As a result, the iron pipe does not get damaged easily. Thus, rusting on galvanised iron is prevented by the coating of zinc.

On the other hand, zinc is more electropositive than tin. If the coating of tin is broken anywhere, or any pores or breaks are observed on the pipe, the parts where the iron is exposed are rusted easily.

Q.4. What do you mean by Kohlrausch’s law: from the following molar conductivities at infinite dilution  
λ m Ba (OH)2 = 457.6 Ω-1cm2mol-1

λ m BaCl2 = 240.6 Ω-1cm2mol-1

λ m NH4Cl = 129.8 Ω-1cm2mol-1

Calculate λ m for NH4OH.

Ans. According to Kohlrausch’s Law, “An infinite dilution of each ion migrates independently of its co-ion and makes its own contribution to the total molar conductivity of an electrolyte irrespective of nature.”

Fdsd λ mNH4OH = λ m + λ m

= NH4+ + Cl + 12 Ba2+ +2 OH 12 Ba2+ + Cl

= λ m(NH4Cl) + 12 mBaOH2 12 mBaCl2

= λ m(NH4OH)

= 129.8 +12×457.6-12×240.6

= 238.3 Ω-1cm2mol-1

Important Questions Of Chapter 3 Chemistry Class 12

Class 12 Chemistry Chapter 3 Important Questions – Topics Covered

The topics covered in Class 12 Chemistry Chapter 3 Important questions here are listed below:

  • Electrochemical cells
  • Galvanic cells
  • Measurement of electrode potential
  • Nernst equation
  • The equilibrium constant from the Nernst equation
  • Electrochemical cells and Gibbs free energy of the reaction
  • The conductance of the electrolytic cells
  • Measurement of the conductivity of the ionic solution
  • Kohlrausch’s law

Benefits Of Class 12 Electrochemistry Important Questions

Class 12 Chemistry Chapter 3 Important Questions on Electrochemistry provides a better understanding of the type of question frequently asked in the board exam. This set of questions will help students revise important concepts and apply them in chemical equations. These questions follow the CBSE Syllabus and guidelines, which makes the question set a reliable study material. In addition to that, these questions will be helpful for students who are preparing for competitive exams like NEET and JEE (main). 


Electrochemistry is a subdiscipline of chemistry where the relations between chemical energy and electric energy are studied. Students need to grasp each and every topic very well. These Important Questions will help them enhance their exam preparation and score better marks on the exam.

FAQs (Frequently Asked Questions)

1. Define negative standard electrode potential and positive standard electrode potential.

Negative standard electrode potential means the tendency to get oxidised is greater than hydrogen. Positive standard electrode potential means the tendency to get reduced more than hydrogen.

2. What are the units of molar conductivity?

The units of molar conductivity are: cm2ohm-1mol-1 and Scm2mol-1.

3. Is it safe to stir AgNO3 solution with a copper spoon?

The AgNO3 solution reacts with copper. So, the emf will be positive. Hence, it is not safe to stir AgNO3 solution with a copper spoon.

4. Name the factors that influence the emf of a cell.

The factors that influence the emf are as follows: 

  • the nature of the reactants, 
  • temperature and 
  • the concentration of the solution in two half-cells.