Vidaara.orgClass 12 · Chemistry
CodeVID-C12-03-T1-01
Electrochemical Cells & EMF — Assignment
Name: ____________________
Roll No.: __________
Date: ____________
General Instructions
- All questions are compulsory.
- Section A carries 1 mark each, Section B 2 marks, Section C 3 marks and Section D 5 marks.
- Show all steps in numericals and write balanced half-reactions where asked. For full solutions, raise your doubts with your teacher.
Section A — Multiple Choice Questions
5 × 1 = 5 marks
1.
In a Daniell cell, the cathode is the:
- A.zinc electrode
- B.copper electrode
- C.salt bridge
- D.platinum electrode
2.
Cell EMF is given by:
- A.$E_{anode} - E_{cathode}$
- B.$E_{cathode} - E_{anode}$
- C.$E_{cathode} + E_{anode}$
- D.$E_{cathode} \times E_{anode}$
3.
The Faraday constant is approximately:
- A.$9650\,\text{C}$
- B.$96500\,\text{C mol}^{-1}$
- C.$1.6 \times 10^{-19}\,\text{C}$
- D.$6.02 \times 10^{23}$
4.
A negative standard reduction potential indicates a species that is a:
- A.strong oxidising agent
- B.strong reducing agent
- C.neutral species
- D.non-electrolyte
5.
The SHE uses hydrogen gas at:
- A.$0.1\,\text{bar}$
- B.$1\,\text{bar}$
- C.$10\,\text{bar}$
- D.$100\,\text{bar}$
Section B — Short Answer (2 marks)
3 × 2 = 6 marks
6.
Write the two half-reactions of the Daniell cell.
7.
State the relation between cell EMF and Gibbs energy.
8.
Calculate $E^0_{cell}$ for a cell with $E^0_{cathode} = +0.80\,\text{V}$ and $E^0_{anode} = -0.44\,\text{V}$.
Section C — Short Answer (3 marks)
2 × 3 = 6 marks
9.
What is a standard hydrogen electrode? Why is it needed?
10.
State the Nernst equation and explain each term.
Section D — Long Answer (5 marks)
1 × 5 = 5 marks
11.
Describe the construction and working of a Daniell cell. Write the cell representation and calculate its $\Delta G^0$ given $E^0_{cell} = 1.10\,\text{V}$ and $n = 2$.
Answer Key
Section A — Multiple Choice Questions
- (B) copper electrode
- (B) $E_{cathode} - E_{anode}$
- (B) $96500\,\text{C mol}^{-1}$
- (B) strong reducing agent
- (B) $1\,\text{bar}$
Section B — Short Answer (2 marks)
- Anode: $\text{Zn} \rightarrow \text{Zn}^{2+} + 2e^-$; Cathode: $\text{Cu}^{2+} + 2e^- \rightarrow \text{Cu}$.
- $\Delta G = -nFE_{cell}$; a positive EMF gives a negative $\Delta G$ (spontaneous).
- $E^0_{cell} = 0.80 - (-0.44) = 1.24\,\text{V}$.
Section C — Short Answer (3 marks)
- Pt black with $\text{H}_2$ at 1 bar in 1 M $\text{H}^+$ at 298 K; its $E^0$ is defined as 0, giving a reference to measure all other electrode potentials.
- $E = E^0 - \frac{0.059}{n}\log Q$: $E^0$ standard EMF, $n$ electrons transferred, $Q$ reaction quotient, at 298 K.
Section D — Long Answer (5 marks)
- Zn in $\text{ZnSO}_4$ (anode), Cu in $\text{CuSO}_4$ (cathode), salt bridge joins them; cell: $\text{Zn}\mid\text{Zn}^{2+}\parallel\text{Cu}^{2+}\mid\text{Cu}$; $\Delta G^0 = -2 \times 96500 \times 1.10 = -212.3\,\text{kJ mol}^{-1}$.
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