Redox Reactions - Result Question 1
####1. $Zn$ gives $H_2$ gas with $H_2 SO_4$ and $HCl$ but not with $HNO_3$ because
[2002]
(a) $Zn$ acts as an oxidising agent when it reacts with $HNO_3$
(b) $HNO_3$ is weaker acid than $H_2 SO_4$ and $HCl$
(c) In electrochemical series, $Zn$ is above hydrogen
(d) $NO_3^{-}$is reduced in preference to hydronium ion
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Solution:
- (d) Zinc gives $H_2$ gas with dil $H_2 SO_4 / HCl$ but not with $HNO_3$ because in $HNO_3, NO_3{ }^{-}$ion is reduced and give $NH_4 NO_3, N_2 O, NO$ and $NO_2$
$ \begin{aligned} & . \begin{bmatrix} {[Zn+\underset{\text{ nearly } 6 %)}{2 HNO_3}.} \end{matrix} ) Zn(NO_3)_3+2 H] \times 4 \\ & HNO_3+8 H \longrightarrow NH_3+3 H_2 O \\ & NH_3+HNO_3 \longrightarrow NH_4 NO_3 \\ & 4 Zn+10 HNO_3 \longrightarrow 4 Zn(NO_3)_2+NH_4 NO_3+3 H_2 O \end{aligned} $
$Zn$ is above of hydrogen in electrochemical series. So, $Zn$ displaces $H_2$ from dilute $H_2 SO_4$ and $HCl$ with liberation of $H_2$.
$Zn+H_2 SO_4 \to ZnSO_4+H_2$
