ElectrochemistryHard

Question

By how much would the oxidizing power of MnO4− /Mn2+ couple change if the H+ ions concentration is decreased 100 times at 25°C?

Options

A.increases by 189 mV
B.decreases by 189 mV
C.will increase by 19 mV
D.will decrease by 19 mV

Solution

$MnO_{4}^{-} + 8H^{+} + 5e^{-} \rightleftharpoons Mn^{2 +} + 4H_{2}O$

$\Delta E = - \frac{0.059}{5}.\log\frac{1}{1 \times \left\lbrack H^{+} \right\rbrack^{8}} = - \frac{0.059}{5}.\log\frac{1}{(0.01)^{8}} = - 0.1888\text{ V}$

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