Class 12 Electrochemistry worksheet

Sample questions

Real questions from this chapter, as the app sets them. Tap Answer to see the answer and working.

Section A · multiple choice

1. 1.

   In a galvanic cell, oxidation takes place at the:

   1. salt bridge
   2. external wire
   3. cathode
   4. anode

   Answer

   (d) anode

2. 2.

   The standard emf of the cell Fe | Fe²⁺ || Pb²⁺ | Pb is: (E°: Fe²⁺/Fe = −0.44 V, Pb²⁺/Pb = −0.13 V)

   1. 0.31 V
   2. −0.57 V
   3. −0.31 V
   4. 0.62 V

   Answer

   (a) 0.31 V

   E°cell = E°(cathode) − E°(anode)

3. 3.

   A cell reaction involves 2 electrons and has E°cell = 0.11 V. Its standard Gibbs energy change is: (F = 96,500 C/mol)

   1. −21,230 kJ/mol
   2. 21.23 kJ/mol
   3. −10.62 kJ/mol
   4. −21.23 kJ/mol

   Answer

   (d) −21.23 kJ/mol

   ΔG° = −nFE° = −2 × 96,500 × 0.11 J

Section B · short answer

1. 4.

   What is the function of a salt bridge?

   Answer

   It completes the inner circuit by letting ions move between the half-cells, and it keeps each half-cell electrically neutral, so the cell keeps working.

2. 5.

   For the cell Mg | Mg²⁺ || Ni²⁺ | Ni, find E°cell and ΔG°, and say whether the reaction is spontaneous. (E°: Mg²⁺/Mg = −2.37 V, Ni²⁺/Ni = −0.25 V) (F = 96,500 C/mol)

   Answer

   E° = 2.12 V; ΔG° = −409.16 kJ/mol; spontaneous

   n = 2; ΔG° = −nFE°

Section C · long answer

1. 6.

   Describe the Daniell cell: its set-up, electrode reactions and emf.

   Answer

   A zinc rod dips in ZnSO₄ solution and a copper rod in CuSO₄ solution; the solutions are joined by a salt bridge and the rods by a wire. Anode: Zn → Zn²⁺ + 2e⁻; cathode: Cu²⁺ + 2e⁻ → Cu. Overall Zn + Cu²⁺ → Zn²⁺ + Cu. Standard emf = 0.34 − (−0.76) = 1.10 V.

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