Question

Zn gives hydrogen with sulphuric acid and hydrochloric acid but not with nitric acid because?
(a) Zn acts as an oxidising agent when it reacts with nitric acid.
(b) Nitric acid is a weaker acid than sulphuric acid and hydrochloric acid.
(c) Zn is above the hydrogen in electrochemical series
(d) \[NO_{3}^{-}\]is reduced in preference to \[{{H}^{+}}\]ion

Answer 1

Hint: Acids generally oxidise Zinc and it itself gets reduced to hydrogen gas. But in case of strong oxidising acids, this is not the case.

Complete step by step solution:
-In electrochemical series, Zinc is actually above hydrogen in electrochemical series. Thus it can react with acids and give its salt and hydrogen gas. Thus when it reacts with sulphuric acid and hydrochloric acid it gives hydrogen gas. Their reaction is given as follows

\[Zn+2HCl\to ZnC{{l}_{2}}+{{H}_{2}}\uparrow \]

\[Zn+{{H}_{2}}S{{O}_{4}}\to ZnS{{O}_{4}}+{{H}_{2}}\uparrow \]

-We know Nitric acid is a strong oxidising agent. So, when it reacts with the metal zinc, hydrogen gas is not released. This is because the hydrogen produced during the reaction is oxidised to water by nitric acid. So, instead of reduction of\[{{H}^{+}}\], like all the other reactions of acid with zinc, here \[NO_{3}^{-}\]is reduced and \[{{H}^{+}}\]is oxidised to water. While this reaction occurs, we can see reddish brown gas of nitrogen dioxide. The reaction of zinc with nitric acid is as follows

\[Zn+4HN{{O}_{3}}\to Zn{{(N{{O}_{3}})}_{2}}+2N{{O}_{2}}\uparrow +2{{H}_{2}}O\]


Additional Information: Out of the three acids, hydrochloric acid, sulphuric acid and nitric acid, HCl is the strongest acid. But a strong oxidising agent is nitric acid. When nitric acid and hydrochloric acid are mixed in a 1:3 ratio, this mixture can oxidise even the most stable metal like gold and platinum.

Note: Usually when Zn reacts with acid, it acts as a reducing agent which gets oxidised to a salt and the acid is the oxidising agent which gets reduced to hydrogen gas. When strong acids are involved, it can oxidise even the hydrogen produced.