Question

Copper containing alloy of weight $0.3175g$ is dissolved in an acid and an excess of $KI$ is added. Estimation of copper in alloy is based on the following reaction:

$2C{u}^{2+}\left(aq\right)+5I^{-}\left(aq\right)\to C{u}_2{I}_2\left(s\right)+I_3^{-}\left(aq\right)$

${I_3}^{-}\left(aq\right)+2{S_2{O}_3}^{2-}\left(aq\right)\to {S_4{O}_6}^{2-}\left(aq\right)+3I^{-}\left(aq\right)$

Oxidising agent ($O$) and reducing agent ($R$) in the above reaction are :

• A. $\left(O\right)C{u}^{2+},{S_2{O}_3}^{2-},\left(R\right){I_3}^{-},I^{-}$
• B. $\left(O\right)C{u}^{2+},{S_2{O}_3}^{2-},\left(R\right){I_3}^{-}$
• C. $\left(O\right)C{u}^{2+},{I_3}^{-},\left(R\right)I^{-},{S_2{O}_3}^{2-}$
• D. $\left(O\right)C{u}^{2+},I^{-},\left(R\right){I_3}^{-},{S_2{O}_3}^{2-}$

Answer 1

Answer: (C)

$\left(O\right)C{u}^{2+},{I_3}^{-},\left(R\right)I^{-},{S_2{O}_3}^{2-}$

The oxidation number of copper changes from $+2$ to $+1$. Hence, $C{u}^{2+}$ is reduced and acts as an oxidizing agent.

The oxidation number of iodine changes from $-\frac{1}{3}$ to $-1$. Hence, $I_3^{-}$ is reduced and acts as an oxidizing agent.

The oxidation number of iodine changes from $-1$ to $-\frac{1}{3}$. Hence, $I^{-}$ is oxidized and acts as a reducing agent.

The oxidation number of sulfur changes from $+2$ to $+6$. Hence, $S_2{O}_3^{2-}$ is oxidized and acts as a reducing agent.

hence, the correct option is C