Important Questions for CBSE Board Exam Class 12 Chemistry Chapter 2 - Solutions 2023-24

1.     What is a Galvanic cell?

Ans: It is a device that converts chemical energy of some redox reactions to electrical energy. E.g. Daniel cell, Dry cell etc.

2.      Write the representation of a Daniel cell. Also write its anode reaction, cathode reaction and net reaction?

Ans: Representation of Daniel cell: Zn|Zn2+||Cu2+|Cu Anode reaction: Zn → Zn2+ + 2 e– Cathode reaction: Cu2+ + 2 e → Cu Net reaction: Zn + Cu2+ → Zn2+ + Cu

3.      Write the Nernst equation for a Daniel cell.

Ans: Ecell = E0 cell + 0.0591 log [Cu2+] 2 [Zn2+]

4. How does molar conductivity of a solution changes with dilution?

Ans: The molar conductivity increases with dilution for both strong and weak electrolytes. This is due to the increase in ionic mobility, for strong electrolytes and increase in degree of dissociation, for weak electrolytes.

4.       State Kohlrausch’s law of independent migration of ions.

Ans: It states that the limiting molar conductivity of an electrolyte is the sum of the individual contributions of the anion and the cation of the electrolyte.

5.      λ 0 m for NaCl, HCl and NaAc are 126.4, 425.9 and 91.0 S cm2 mol–1 respectively. Calculate λ 0 m for HAc.

Ans: Given λ 0m (NaCl) = 126.4 Scm2mol–1 , λ 0m (HCl) = 425.9 Scm2mol–1 and λ 0m (NaAc) = 91.0 Scm2mol–1 On applying Kohlrausch’s law, λ 0m(HAc) = λ 0m (NaAc) + λ 0m (HCl) – λ 0m (NaCl) = 91.0 + 425.9 – 126.4 = 390.5 Scm2mol-1

6.    Write any two differences between primary cell and secondary cell.

Ans: Primary cell Secondary cell Cannot be recharged or reused Can be recharged and reused. The cell reaction cannot be reversed The cell reaction can be reversed. E.g. Dry cell, Mercury cell E.g.: Lead storage cell, NiCad cell

7.    Write the anode and cathode reactions occur in the operation of a lead storage battery. Mention the electrolyte used in the battery.

 Ans: Anode reaction: Pb + SO4 2– → PbSO4 + 2e– Cathode reaction: PbO2 + SO4 2– + 4H+ + 2e– → PbSO4 + 2H2O Net reaction: Pb + PbO2 + 2 H2SO4 → 2 PbSO4 + 2 H2O Electrolyte used is 38% H2SO4 .

8.    What is a fuel cell?

Ans: Fuel cells are galvanic cells which convert the energy of combustion of fuels (like hydrogen, methane, methanol etc.) directly into electrical energy.

9.   Diagrammatically represent H2 – O2 fuel cell. Write the anode reaction, cathode reaction and overall cell reaction taking place in it?

Ans: H2– O2 fuel cell Anode reaction: 2H2 (g) + 4OH– (aq) → 4H2O(l) + 4e–

Cathode reaction: O2(g) + 2H2O(l ) + 4e–→ 4OH– (aq) Net Reaction: 2H2(g) + O2(g) → 2 H2O(l ) 

11. Write any two advantages of fuel cells.

Ans: It is highly efficient and it is eco-friendly.

12. What is corrosion? Write any two methods to prevent the corrosion (rusting) of iron.

Ans: It is the process of formation of oxide or other compounds of a metal on its surface by the action of air, water-vapour, CO2 etc. Rusting can be prevented by (i) coating the metal surface with paint, varnish etc. (ii) coating with anti-rust solution.