NCERT Solutions for Class 12 Chemistry Chapter 3: Electrochemistry

Electrochemistry is an important chapter in Class 12 Chemistry that explains the relationship between electricity and chemical reactions. This chapter helps students understand how electrochemical cells work, including galvanic and electrolytic cells, and their applications in real life. Below is a structured breakdown of the key topics covered in this chapter.

NCERT Solutions for Class 12 Chemistry Chapter 3 Overview

Section	Topic Name
3	Electrochemistry
3.1	Electrochemical Cells
3.2	Galvanic Cells
3.3	Nernst Equation
3.4	Conductance of Electrolytic Solutions
3.5	Electrolytic Cells and Electrolysis
3.6	Batteries
3.7	Fuel Cells
3.8	Corrosion

NCERT Solutions for Class 12 Chemistry Chapter 3 Electrochemistry

NCERT solutions provide detailed and step-by-step explanations of all important concepts in this chapter. These solutions help students build a strong foundation in electrochemistry and prepare well for board exams and competitive exams like JEE and NEET.

Electrochemistry Chapter Full Solution:

Question 1. How would you determine the standard electrode potential of the system Mg²⁺ | Mg?
Solution:
Set up an electrochemical cell consisting of MglMgSO₄(1 M) as one electrode by dipping a magnesium wire in 1 M MgSO₄ solution and standard hydrogen electrode Pt, H₂ (1 atm) | H⁺(1 M) as the second electrode. Measure the EMF of the cell and also note the direction of deflection in the voltmeter. The direction of deflection shows that the electrons flow from magnesium electrode to hydrogen electrode, i.e., oxidation takes place on magnesium electrode and reduction on hydrogen electrode.

Question 2. Can you store copper sulphate solution in a zinc pot ?
Solution:

Question 3. Consult the table of standard electrode potentials and suggest three substances that can oxidise ferrous ions under suitable conditions.
Solution:
Oxidation of ferrous ions means :

Only those substances can oxidise Fe²⁺ to Fe³⁺ which are stronger oxidising agents and have positive reduction potentials greater than 0.77 V so that EMF of the cell reaction is positive. This is for elements lying below Fe³⁺/Fe²⁺ in the electrochemical series, for example, Br₂, Cl₂ and F₂.

Question 4. Calculate the potential of hydrogen electrode in contact with a solution whose pH is 10.
Solution:

Question 5. Calculate the emf of the cell in which the following reaction takes place :
Ni_(S) + 2Ag⁺ (0.002 M) → Ni²⁺(0.160 M) + 2Ag_(S)
Given that E°cell = 1.05 V

Solution:

Question 6. The cell in which the following reaction occurs: 2Fe³⁺_(aq) + 2l^–_(aq) → 2Fe²⁺_(aq) + l_2(s) has E°cell = 0.236 V at 298 K. Calculate the standard Gibb’s energy and the equilibrium constant of the cell reaction.
Solution:

Question 7. Why does the conductivity of a solution decrease with dilution?
Solution: The conductivity of a solution is linked with the number of ions present per unit volume. With dilution, these decrease and the corresponding conductivity or specific conductance of the solution decreases.

Question 8.  Suggest a way to determine the value of water.
Ans:

Question 9. The molar conductivity of 0.025 mol L^-1 methanoic acid is 46.1 S cm² mol^-1. Calculate its degree of dissociation and dissociation constant Given λ^°(H⁺)=349.6 S cm² mol^-1 andλ^°(HCOO-) = 54.6 S cm² mol^-1
Solution:

Question 10. If a current of 0.5 ampere flows through a metallic wire for 2 hours, then how many electrons would flow through the wire?
Solution:

Question 11. Suggest a list of metals which can be extracted electrolytically.
Solution: The highly reactive metals having large -ve E° values, which can themselves act as powerful reducing agents can be extracted electrolytically. The process is known as electrolytic reduction. For details, consult Unit-6. For example, sodium, potassium, calcium, magnesium etc.

Question 12. Consider the reaction: Cr₂O₇^2--+ 14H⁺ + 6e- -> 2Cr₃+ + 7H₂O What is the quantity of electricity in coulombs needed to reduce 1 mol of Cr₂O₇^2- ?
Solution:

Question 13. Write the chemistry of recharging the lead storage battery, highlighting all the materials that are involved during recharging.
Solution: A lead storage battery consists of anode of lead, cathode of a grid of lead packed with lead dioxide (PbO₂) and 38% H₂SO₄ solution as electrolyte. When the battery is in use, the reaction taking place are:

On charging the battery, the reverse reaction takes place, i.e., PbSO₄ deposited on electrodes is converted back to Pb and PbO₂ and H₂SO₄ is regenerated.

Question 14. Suggest two materials other than hydrogen that can be used as fuels in the fuel cells.
Solution: Methane (CH₄) and methanol (CH₃OH) can also be used as fuels in place of hydrogen in the fuel cells.

Question 15. Explain how rusting of iron is envisaged as setting up of an electrochemical cell.
Solution: The water present on the surface of iron dissolves acidic oxides of air like CO₂ , SO₂ , etc. to form acids which dissociate to give H⁺ ions :

Thus, an electrochemical cell is set up on the surface.
Ferrous ions are further oxidised by atmospheric oxygen to ferric ions which combine with water to form hydrated ferric oxide, Fe₂O₃. xH₂O, which is rust.

NCERT EXERCISES

Question 1. Arrange the following metals in the order in which they displace each other from their salts.
Al, Cu, Fe, Mg and Zn
Solution: Mg, Al, Zn, Fe, Cu.

Question 2. Given the standard electrode potentials,
K⁺/ K = – 2.93 V, Ag⁺/ Ag = 0.80 V, Hg²⁺/ Hg = 0.79 V, Mg²⁺/ Mg = -2.37 V, Cr³⁺/ Cr = – 0.74 V
Arrange these metals in their increasing order of reducing power.
Solution:
Higher the oxidation potential, more easily it is oxidized and hence greater is the reducing power. Thus, increasing order of reducing power will be
Ag < Hg < Cr < Mg < K.

Question 3. Depict the galvanic cell in which the reaction Zn_(S) + 2Ag⁺_(aq) Zn²⁺_(aq), + 2Ag_(s) takes place. Further show :

1. Which of the electrode is negatively charged?
2. The carriers of the current i n the cell.
3. Individual reaction at each electrode.

Solution:

Question 4. Calculate the standard cell potentials of galvanic cell in which the following reactions take place :

Solution:

Question 5. Write the Nernst equation and emf of the following cells at 298 K :

Solution:

Question 6. In the button cells widely used in watches and other devices the following reaction takes place :

Solution:

Question 7. Define conductivity and molar conductivity for the solution of an electrolyte. Discuss their variation with concentration.
Solution:
The reciprocal of resistivity is known as specific conductance or simply conductivity. It is denoted by K (kappa). Thus, if K is the specific conductance and G is the conductance of the solution, then

Now, if I = 1 cm and A = lsq.cm, then K = G.

Hence, conductivity of a solution is defined as the conductance of a solution of 1 cm length and having 1 sq. cm as the area of cross¬section. Alternatively, it may be defined as conductance of one centimetre cube of the solution of the electrolyte.

Molar conductivity of a solution at a dilution V is the conductance of all the ions produced from 1 mole of the electrolyte dissolved in V cm³ of the solution when the electrodes are one cm apart and the area of the electrodes is so large that the whole of the solution is contained between them. It is represented by ∆_m.

Variation of conductivity and molar conductivity with concentration: Conductivity always decreases with decrease in concentration, for both weak and strong electrolytes. This is because the number of ions per unit volume that carry the current in a solution decreases on dilution.

Molar conductivity increases with decrease in concentration. This is because that total volume, V, of solution containing one mole of electrolyte also increases. It has been found that decrease in K on dilution of a solution is more than compensated by increase in its volume.

Question 8. The conductivity of 0.20 M solution of KCl at 298 K is 0.0248 S cm^-1. Calculate its molar conductivity.
Solution:

Question 9. The resistance of a conductivity cell containing 0.001 M KCI solution at 298 K is 1500 Ω What is the cell constant if conductivity of 0.001 M KCI solution at 298 K is 0.146 x 10^-3 S cm^-1?
Solution:

Question 10. The conductivity of NaCl at 298 K has been determined at different concentrations and the results are given below:

Solution:

Question 11. Conductivity of 0.00241 M acetic acid is 7.896 × 10^-5 S cm^-1. Calculate its molar conductivity. If ∆°_m for acetic acid is 390.5 S cm² mol^-1, what is its dissociation constant?
Solution:

Question 12. How much charge is required for the following reductions:

1. 1 mol of Al³⁺to Al ?
2. 1 mol of Cu²⁺ to Cu ?
3. 1 mol of MnO₄^– to Mn²⁺ ?

Solution:

Question 13. How much electricity in terms of Faraday is required to produce

1. 20.0 g of Ca from molten CaCl₂?
2. 40.0 g of Al from molten Al₂O₃?

Solution:

Question 14. How much electricity is required in coulomb for the oxidation of

1. 1 mol of H₂O to O₂?
2. 1 mol of FeO to Fe₂O₃?

Question 15. A solution of Ni(NO₃)₂ is electrolysed between platinum electrodes using a current of 5 amperes for 20 minutes. What mass of Ni is deposited at the cathode?
(At. mass of Ni = 58.7)
Solution:

Question 16. Three electrolytic cells A, B, C containing solutions of ZnSO₄, AgNO₃ and CuSO₄ respectively are connected in series. A steady current of 1.5 amperes was passed through them until 1.45 g of silver deposited at the cathode of cell B. How long did the current flow? What mass of copper and zinc were deposited?
(At. wt. of Ag = 108, Cu = 63.5, Zn = 65.3)
Solution:

Question 17. Using the standard electrode potentials predict if the reaction between the following is feasible :

Solution: A particular reaction can be feasible if e.m.f. of the cell based on the E° values is positive. Keeping this in mind, let us predict the feasibility of the reactions.

Question 18. Predict the product of electrolysis in each of the following:

1. An aqueous solution of AgNO₃ with silver electrodes.
2. An aqueous solution of AgNO₃ with platinum electrodes.
3. A dilute solution of H₂SO₄ with platinum electrodes.
4. An aqueous solution of CuCI₂ with platinum electrodes.

Solution:

• Chapter 1 The Solid State
• Chapter 2 Solutions
• Chapter 3 Electro chemistry
• Chapter 4 Chemical Kinetics
• Chapter 5 Surface Chemistry
• Chapter 6 General Principles and Processes of Isolation of Elements
• Chapter 7 The p Block Elements
• Chapter 8 The d and f Block Elements
• Chapter 9 Coordination Compounds
• Chapter 10 Haloalkanes and Haloarenes
• Chapter 11 Alcohols Phenols and Ethers
• Chapter 12 Aldehydes Ketones and Carboxylic Acids
• Chapter 13 Amines
• Chapter 14 Biomolecules
• Chapter 15 Polymers
• Chapter 16 Chemistry in Everyday Life

Conclusion

NCERT Solutions for Class 12 Chemistry Chapter 3: Electrochemistry are an invaluable resource for students aiming to excel in their board exams and competitive tests. These solutions provide clear and concise answers to all textbook questions, helping you understand the concepts thoroughly. Download the PDF today and start practicing to ace your exams!