First slide

Activity Series (OR) Electro chemicals series

Question

Zn gives $H_{2}$ gas with $H_{2} {SO}_{4}$ and HCl but not with ${HNO}_{3}$ because

Moderate

A

Zn acts as an oxidising agent when it reacts with ${HNO}_{3}$
B

$H N O_{3}$ 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.

Solution

Zinc gives $H_{2}$ gas with dil. $H_{2} {SO}_{4}$ /HCl but not with ${HNO}_{3}$ because in ${HNO}_{3}$ , ${NO}_{3}^{⊝}$ , NO and ${NO}_{2}^{}$ (based upon the concentration of ${HNO}_{3}$ )
$[Zn + {HNO}_{3} \overset{}{\to} Zn {({NO}_{3})}_{2} + 2 H] \times 4$
(nearly 6%)
${HNO}_{3} + 8 H^{+} \to {NH}_{3} + 3 H_{2} O$
${NH}_{3} + HN O_{3} \overset{}{\to} {NH}_{4} {NO}_{3}$
$Zn + 10 {HNO}_{3} \overset{}{\to} 4 Zn {({NO}_{3})}_{2} + {NH}_{4} {NO}_{3} + 3 H_{2} O$
Zn ishaving lesser reduction potential than hydrogen in electrochemical series. So Zn displaces $H_{2}$ from dilute $H_{2} {SO}_{4}$ and HCl

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