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The p-Block Elements
Oxidising Action of Nitric Acid
1 question from 1 paper, each with its answer.
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- of The p-Block Elements
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Concepts tested
- Nitrate reduced instead of H+
All Questions
2002 AIPMT 1 question
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Zn gives $H_2$ gas with $H_2SO_4$ and HCl but not with $HNO_3$ because :-With dilute $H_2SO_4$ or HCl, zinc reduces $H^+$ (hydronium) ions to hydrogen gas: $Zn + 2H^+ \rightarrow Zn^{2+} + H_2$.
Nitric acid is a strong oxidising agent. The nitrate ion is reduced more easily than $H^+$ (it has a higher reduction potential).
So zinc reduces $NO_3^-$ to oxides of nitrogen, $N_2O$, or $NH_4^+$ instead of releasing hydrogen; any hydrogen formed is also oxidised to water.
Example: $4Zn + 10HNO_3(dil) \rightarrow 4Zn(NO_3)_2 + N_2O + 5H_2O$
$HNO_3$ is a strong acid, and Zn acts as a reducing agent, not an oxidising agent.
So $NO_3^-$ is reduced in preference to the hydronium ion.