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Equivalent, Molar Conductivity and Cell Constant

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Question

The value for the standard emf (electromotive force) of a galvanic cell described by the balanced chemical equation is $0.79 V$ . Determine the value of the standard half-cell potential for the $I^{-} / I_{2}$ couple.
$C r_{2} O_{7}^{2 -} (a q) + 2 I^{-} (a q) \to I_{2} (g) + C r^{3 +} (a q)$
$E_{C r_{2} O_{7}^{2 -} / C r^{3 +}}^{\circ} = 1.33 V$

+ 0.18 V

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- 0.18 V

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0.54 V

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- 0.54 V

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Solution

The correct option is C $0.54 V$
In the given reaction, $I^{-}$ has been oxidised to $I_{2}$ and $C r_{2} O_{7}^{2 -}$ ions have been reduced to $C r^{3 +}$

$E_{c e l l}^{\circ} = SRP of substance reduced - SRP of substance oxidised$
(SRP - Standard reduction potential)

$E_{c e l l}^{\circ} = E_{c a t h o d e (r e d)}^{\circ} - E_{a n o d e (r e d)}^{\circ}$

$E_{c e l l}^{\circ} = E_{C r_{2} O_{7}^{2 -} / C r^{3 +}}^{\circ} - E_{I^{-} / I_{2}}^{\circ}$

$0.79 = 1.33 - E_{I^{-} / I_{2}}^{\circ}$

$E_{I^{-} / I_{2}}^{\circ} = 0.54 V$

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