Question
Hot concentrated sulphuric acid is a moderately strong oxidising agent. Which of the following reaction does not show oxidising behaviour?
A.
$$Cu + 2{H_2}S{O_4} \to CuS{O_4} + S{O_2} + 2{H_2}O$$
B.
$$3S + 2{H_2}S{O_4} \to 3S{O_2} + 2{H_2}O$$
C.
$$C + 2{H_2}S{O_4} \to C{O_2} + 2S{O_2} + 2{H_2}O$$
D.
$$Ca{F_2} + {H_2}S{O_4} \to CaS{O_4} + 2HF$$
Answer :
$$Ca{F_2} + {H_2}S{O_4} \to CaS{O_4} + 2HF$$
Solution :
Key Idea An oxidising agent is a species, which oxidises the other species and itself gets reduced.
\[\begin{align}
& \left( \text{i} \right)C\overset{0}{\mathop{u}}\,+2{{H}_{2}}S{{O}_{4}}\to \overset{+2}{\mathop{Cu}}\,S{{O}_{4}}+S{{O}_{2}}+2{{H}_{2}}O \\
& \left( \text{ii} \right)3\overset{0}{\mathop{S}}\,+2{{H}_{2}}S{{O}_{4}}\to \overset{+4}{\mathop{3S{{O}_{2}}}}\,+2{{H}_{2}}O \\
& \left( \text{iii} \right)\overset{0}{\mathop{C}}\,+{{H}_{2}}S{{O}_{4}}\to \overset{+4}{\mathop{C{{O}_{2}}}}\,+2S{{O}_{2}}+2{{H}_{2}}O \\
& \left( \text{iv} \right)\overset{+2}{\mathop{C}}\,a{{\overset{-1}{\mathop{F}}\,}_{2}}+{{H}_{2}}S{{O}_{4}}\to \overset{+2}{\mathop{Ca}}\,S{{O}_{4}}+2H\overset{-1}{\mathop{F}}\, \\
\end{align}\]
In reaction (iv), oxidation number of elements remains unchanged. Thus, in this reaction, $${H_2}S{O_4}$$ does not act as an oxidising agent.