Question

In which of these reactions Sulphuric acid does not act as oxidising agent

• A. Sulphuric acid $+$Zinc
• B. Sulphuric acid $+$Sodium hydroxide
• C. Sulphuric acid $+$Sodium chloride
• D. Sulphuric acid $+$Carbon.

Answer 1

The correct option is B

Sulphuric acid $+$Sodium hydroxide

The explanation for the correct answer

Option B: Sulphuric acid $+$Sodium hydroxide

1. $$\begin{gathered} {\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)+2\mathrm{NaOH}\left(\mathrm{aq}\right)\to {\mathrm{Na}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right) \\ \mathrm{Sulphuric}\mathrm{acid}+\mathrm{Sodium}\mathrm{hydroxide}\to \mathrm{Sodium}\mathrm{sulphate}+\mathrm{Water} \end{gathered}$$, it is a double displacement reaction, also a neutralization reaction because acid reacts with the base to form salt and water.
2. In a double displacement reaction, there is no transfer of electrons takes place, simply there is a transfer of molecule from one compound to other. So double displacement reaction is not a redox reaction.
3. In neutralization reaction also there is no transfer of electrons takes place. So it is also not a redox reaction.
4. So, here Sulphuric acid does not act as an oxidizing agent.

The explanation for the incorrect answers

Option A: Sulphuric acid $+$Zinc

1. When $\mathrm{conc}.{\mathrm{H}}_2{\mathrm{SO}}_4$ is heated with $\mathrm{Zn}$metal, the acid gets reduced to ${\mathrm{SO}}_2$, thus acting as an oxidizing agent.
2. e.g. $$\begin{gathered} \mathrm{Zn}\left(\mathrm{s}\right)+2{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)\to {\mathrm{ZnSO}}_4\left(\mathrm{aq}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)+{\mathrm{SO}}_2\left(\mathrm{g}\right). \\ \mathrm{Zinc}+\mathrm{Sulphuric}\mathrm{acid}\to \mathrm{Zinc}\mathrm{sulphate}+\mathrm{Water}+\mathrm{Sulphur}\mathrm{dioxide} \end{gathered}$$

Option C: Sulphuric acid $+$Sodium chloride

1. ${\mathrm{H}}_2{\mathrm{SO}}_4$ oxidizes $\mathrm{NaCl}$ and forms $\mathrm{HCl}$.
2. e.g. $$\begin{gathered} \mathrm{NaCl}\left(\mathrm{aq}\right)+{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)\to {\mathrm{NaHSO}}_4\left(\mathrm{aq}\right)+\mathrm{HCl}\left(\mathrm{aq}\right) \\ \mathrm{Sodium}\mathrm{chloride}+\mathrm{Sulphuric}\mathrm{acid}\to \mathrm{Sodium}\mathrm{bisulphate}+\mathrm{Hydrochloric}\mathrm{acid} \end{gathered}$$

Option D: Sulphuric acid $+$Carbon.

1. ${\mathrm{H}}_2{\mathrm{SO}}_4$ oxidises $\mathrm{C}$ to form ${\mathrm{CO}}_2\mathrm{and}{\mathrm{SO}}_2$.
2. e.g. $$\begin{gathered} \mathrm{C}\left(\mathrm{s}\right)+2{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)\to 2{\mathrm{SO}}_2\left(\mathrm{aq}\right)+{\mathrm{CO}}_2\left(\mathrm{aq}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right) \\ \mathrm{Carbon}+\mathrm{Sulphuric}\mathrm{acid}\to \mathrm{Sulphur}\mathrm{dioxide}+\mathrm{Carbon}\mathrm{dioxide}+\mathrm{Water} \end{gathered}$$

So, the correct option is B. Sulphuric acid does not act as an oxidizing agent when a double displacement reaction takes place.