Electrochemistry Result Question 29
Passage
Redox reaction play a pivotal role in chemistry and biology. The values of standard redox potential $\left(E^{\circ}\right)$ of two half-cell reactions decide which way the reaction is expected to proceed. A simple example is a Daniell cell in which zinc goes into solution and copper gets deposited. Given below are a set of half-cell reactions (acidic medium) along with their $E^{\circ}(V$ with respect to normal hydrogen electrode) values.
(2007, 4 $\times$ 3M = 12M)
$ \mathrm{I}_2+2 e^{-} \rightarrow 2 \mathrm{I}^{-} $$\quad \quad E^{\circ}=0.54 $
$ \mathrm{Cl}_2+2 e^{-} \rightarrow 2 \mathrm{Cl}^{-} $$\quad \quad E^{\circ}=1.36 $
$ \mathrm{Mn}^{3+}+e^{-} \rightarrow \mathrm{Mn}^{2+} $$\quad \quad E^{\circ}=1.50 $
$ \mathrm{Fe}^{3+}+e^{-} \rightarrow \mathrm{Fe}^{2+} $$\quad \quad\quad E^{\circ}=0.77 $
$ \mathrm{O}_2+4 \mathrm{H}^{+}+4 e^{-} \rightarrow 2 \mathrm{H}_2 \mathrm{O} $$\quad \quad E^{\circ}=1.23$
29. Among the following, identify the correct statement.
(a) Chloride ion is oxidised by $\mathrm{O} _2$
(b) $\mathrm{Fe}^{2+}$ is oxidised by iodine
(c) Iodide ion is oxidised by chlorine
(d) $\mathrm{Mn}^{2+}$ is oxidised by chlorine
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Answer:
Correct Answer: 29. ( c )
Solution:
- For spontaneous redox reaction : $E_{\text {cell }}^{\circ}>0$
For
$ \begin{aligned} & 2 \mathrm{I}^{-}+\mathrm{Cl}_2 \longrightarrow 2 \mathrm{Cl}^{-}+\mathrm{I}_2 \\ & E^{\circ}=1.36-0.54=0.82 \mathrm{~V}>0 \end{aligned} $
i.e. $\mathrm{Cl}_2$ will spontaneously oxidise $I^{-}$ .
In other cases $E_{\text {cell }}^{\circ}<0$, they are non-spontaneous.
BETA
