Question

The emf of cell Tl$\vert^{Tl^+}_{_{(0.001M)}}\vert^{Cu^{2+}}_{_{(0.01M)}}$Cu is 0.83 V at 298 K. It could be increased by:

• A. increasing concentration of Tl$^+$ ions
• B. increasing concentration of both Tl$^+$ and Cu$^{2+}$ ions
• C. decreasing concentration of both Tl$^+$ and Cu$^{2+}$ ions
• D. increasing concentration of Cu$^{2+}$ ions

Answer 1

The Correct Option is D

The emf of the cell is given by the Nernst equation:
\[ E = E^\circ - \frac{0.0591}{n} \log \frac{\text{[Products]}}{\text{[Reactants]}}. \]
For the cell:
\[ \text{Tl|Tl}^+ \, || \, \text{Cu}^{2+}| \text{Cu}, \]
the cell reaction is:
\[ \text{Tl} + \text{Cu}^{2+} \rightarrow \text{Tl}^+ + \text{Cu}. \]
Effect of concentration: Increasing the concentration of Cu$^{2+}$ ions (product-side reactant) decreases the denominator in the reaction quotient, shifting the reaction to the right and increasing the emf.
Increasing the concentration of Tl$^+$ ions (reactant-side product) increases the numerator in the reaction quotient, decreasing the emf.
Decreasing concentrations of both ions would reduce the driving force of the reaction, lowering the emf.
Thus, the emf can be increased by: [Increasing the concentration of Cu$^{2+}$ ions (Option 4).]