Question

A galvanic cell is composed of two hydrogen electrodes, one of which is a standard one. In which of the following solutions should the other electrode be immersed to get maximum emf ?

$K_{a}\ (\text{C}\text{H}_{3}\text{COOH})\text{ = 2 }\text{×}\text{ 1}\text{0}^{\text{-5}}\text{ , Ka }(H_{3}\text{P}\text{O}_{4})\text{ = 1}\text{0}^{\text{-3}}\text{ .}$

• A. 0.1 M HCl
• B. 0.1 M CH3COOH
• C. 0.1 M H3PO4
• D. 0.1 M H2SO4

Answer 1

Answer: (B)

0.1 M CH3COOH

Answer 2

$E_{cell} = 0.059\log\frac{C_{1}}{C_{2}}$For Ecell to be +ve and maximum $\frac{C_{1}}{C_{2}} < 1$ or $C_{1}\text{ < }\text{C}_{2}$

Give $C_{2}\text{ = 1M.}$

$\therefore$ C1 should be the minimum conc. of H+.

\ (2) is the right answer.