Zn gives $\mathrm{H}_{2}$ gas with $\mathrm{H}_{2} \mathrm{SO}_{4}$ and $\mathrm{HCl}$ but not with…

Zn gives $\mathrm{H}_{2}$ gas with $\mathrm{H}_{2} \mathrm{SO}_{4}$ and $\mathrm{HCl}$ but not with $\mathrm{HNO}_{3}$ because
  1. $\mathrm{Zn}$ acts as an oxidising agent when it reacts with $\mathrm{HNO}_{3}$
  2. $\mathrm{HNO}_{3}$ is weaker acid than $\mathrm{H}_{2} \mathrm{SO}_{4}$ and $\mathrm{HCl}$
  3. In electrochemical series, $\mathrm{Zn}$ is above hydrogen
  4. $\mathrm{NO}_{3}^{-}$ is reduced in preference to hydronium ion

Solution

Zinc gives $\mathrm{H}_{2}$ gas with dil $\mathrm{H}_{2} \mathrm{SO}_{4} / \mathrm{HCl}$ but not with $\mathrm{HNO}_{3}$ because in $\mathrm{HNO}_{3}, \mathrm{NO}_{3}^{-}$ ion is reduced and give $\mathrm{NH}_{4} \mathrm{NO}_{3}, \mathrm{~N}_{2} \mathrm{O}, \mathrm{NO}$ and
$\mathrm{NO}_{2}$ (based upon the concentration of $\left.\mathrm{HNO}_{3}ight)$
$\left[\mathrm{Zn}+2 \mathrm{HNO}_{3} \longrightarrow \mathrm{Zn}\left(\mathrm{NO}_{3}ight)_{2}+2 \mathrm{H}ight] \times 4$ (nearly 6%)
$\mathrm{HNO}_{3}+8 \mathrm{H} \longrightarrow \mathrm{NH}_{3}+3 \mathrm{H}_{2} \mathrm{O}$
$\mathrm{NH}_{3}+\mathrm{HNO}_{3} \longrightarrow \mathrm{NH}_{4} \mathrm{NO}_{3}$
$4 \mathrm{Zn}+10 \mathrm{HNO}_{3} \longrightarrow 4 \mathrm{Zn}\left(\mathrm{NO}_{3}ight)_{2}+\mathrm{NH}_{4} \mathrm{NO}_{3}+3 \mathrm{H}_{2} \mathrm{O}$
$\mathrm{Zn}$ is on the top position of hydrogen in electrochemical series. So $\mathrm{Zn}$ displaces $\mathrm{H}_{2}$ from dilute $\mathrm{H}_{2} \mathrm{SO}_{4}$ and $\mathrm{HCl}$ with liberation of $\mathrm{H}_{2}$.
$\mathrm{Zn}+\mathrm{H}_{2} \mathrm{SO}_{4} ightarrow \mathrm{ZnSO}_{4}+\mathrm{H}_{2}$

Asked in: JEE-TOPICTESTS-CHEMISTRY

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