Question
To a beaker containing 0.1 M – HCl, a little pure solid AgCl is added. Both a silver and a hydrogen electrode (PH2 = 1.0 bar) are then placed in the solution. What is the approximate value of EMF measured between the electrodes at 25°C? (Given: $E_{Ag^{+}|Ag}^{o}$= 0.80 V and Ksp (AgCl) = 10−10) [2.303 RT/F = 0.06]
Options
Solution
Net cell reaction: $Ag(s) + H^{+} + Cl^{-} \rightleftharpoons AgCl(s) + \frac{1}{2}H_{2}(g)$
But for Ecell calculation, reaction may be written as
$Ag(s) + H^{+} \rightleftharpoons Ag^{+} + \frac{1}{2}H_{2} $$${\text{Now, }E_{cell} = E_{cell}^{o} - \frac{0.06}{1}.\log\frac{\left\lbrack Ag^{+} \right\rbrack.P_{H_{2}}^{1/2}}{\left\lbrack H^{+} \right\rbrack} }{= \lbrack 0 - 0.80\rbrack - \frac{0.06}{1}.\log\frac{\left( \frac{10^{- 10}}{0.1} \right) \times 1^{1/2}}{0.1} = - 0.32\text{ V}}$$
It means that actual reaction is in reverse direction and Ecell = 0.32 V
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