Gujarat BoardEnglish MediumSTD 11 ScienceChemistryRedox Reactions2 Marks
Question
Nitric acid acts only as an oxidising agent while nitrous acid acts both as an oxidising as well as reducing agent. Explain.
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Answer
i. $\mathrm{HNO}_3$
Oxidation number of N in $\mathrm{HNO}_3$ is +5 .
Maximum oxidation number of N is +5 because it has five electrons in the valence shell $\left(2 s^2 2 p^3\right)$.
Minimum oxidation number of N is -3 because it can accept 3 more electrons to get noble gas configuration. Since, oxidation number of N in $\mathrm{HNO}_3$ is maximum, therefore, it can only decrease.
Thus, $\mathrm{HNO}_3$ can act as an oxidising agent.
ii. $\mathrm{HNO}_2$
Oxidation number of $\mathrm{N}=+3$
Maximum oxidation number of $\mathrm{N}=+5$
Minimum oxidation number of $\mathrm{N}=-3$
Therefore, the oxidation number of N can increase by losing electrons or can decrease by accepting electrons. Thus, $\mathrm{HNO}_2$ can act both as an oxidising as well as a reducing agent.
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