The standard reduction potentials at 298 K for the following half cells are given below:

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Solution

Q.
The standard reduction potentials at 298 K for the following half cells are given below: [2024]

$C r_{2} O_{7}^{2 -} + 14 H^{+} + 6 e^{-} \to 2 C r^{3 +} + 7 H_{2} O, E^{0} = 1.33 V$

$F e^{3 +} (a q) + 3 e^{-} \to F e, E^{0} = - 0.04 V$

$N i^{2 +} (a q) + 2 e^{-} \to N i, E^{0} = - 0.25 V$

$A g^{+} (a q) + e^{-} \to A g, E^{0} = 0.80 V$

$A u^{3 +} (a q) + 3 e^{-} \to A u, E^{0} = 1.40 V$

Consider the given electrochemical reactions,

The number of metal(s) which will be oxidized be $C r_{2} O_{7}^{2 -}$ in aqueous solution is __________.

Ans.
(3)

For the above reaction to be spontaneous:

$E_{r e a c t i o n}^{o} = E_{c a t h o d e}^{o} - E_{a n o d e}^{o} > 0$

$E_{C r_{2} O_{7}^{2 -}}^{o} - E_{a n o d e}^{o} > 0$

$1.33 - E_{a n o d e}^{o} > 0$

$E_{a n o d e}^{o} < 1.33 V$

Thus Fe, Ni and Ag will be oxidized by $C r_{2} O_{7}^{2 -}$ .

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