Question
The minimum mass of NaOH required to be added in RHS to consume all the H+ present in RHS of the cell of EMF, +0.70 V at 25°C, before its use. Zn|Zn2+ (0.01 M)||HCl (V = 500 ml)|H2 (1 bar)|Pt
Given: $E_{Zn^{2 +}|Zn}^{o}$= − 0.76 V; 2.303 RT/F = 0.06
Options
Solution
Net cell reaction: $Zn + 2H^{+} \rightleftharpoons Zn^{2 +} + H_{2}$
$E_{cell} = E_{cell}^{o} - \frac{0.06}{2}.\log\frac{\left\lbrack Zn^{2 +} \right\rbrack.P_{H_{2}}}{\left\lbrack H^{+} \right\rbrack^{2}} $$${\text{Or, 0.70 = }\left\lbrack 0 - ( - 0.76) \right\rbrack - \frac{0.06}{2}.\log\frac{0.01 \times 1}{\left\lbrack H^{+} \right\rbrack^{2}} }{\Rightarrow \left\lbrack H^{+} \right\rbrack = 0.01\text{ M}}$$
Moles of HCl in RHS = $\frac{500 \times 0.01}{1000} = 5 \times 10^{- 3}$
∴ Mass of NaOH needed = 5 × 10–3 × 40 = 0.2 gm
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