Ncert Exercises & Solutions

PbO and PbO₂ react with HCl according to following chemical equations

$2 PbO + 4 HCl \to 2 {PbCl}_{2} + 2 H_{2} O$

${PbO}_{2} + 4 HCl \to {PbCl}_{2} + {Cl}_{2} + 2 H_{2} O$

Why do these compounds differ in their reactivity?

Writing the oxidation number of each element above its symbol in the following reactions

(a)

\underset{Basic oxide}{2 \overset{+ 2}{P} \overset{- 2}{bO}} + \underset{Acid}{4 \overset{+ 1}{H} \overset{- 1}{Cl}} \to 2 \overset{+ 2}{Pb} {\overset{- 1}{Cl}}_{2} + 2 {\overset{+ 1}{H}}_{2} \overset{- 2}{O}

In this reaction, oxidation number of each element remains same hence, it is not a redox reaction. In fact, it is an example of acid-base reaction.

(b)

\overset{+ 4}{Pb} {\overset{- 2}{O}}_{2} + 4 \overset{+ 1}{H} \overset{- 1}{Cl} \to \overset{+ 2}{Pb} {\overset{- 1}{Cl}}_{2} + {\overset{0}{Cl}}_{2} + 2 {\overset{+ 1}{H}}_{2} \overset{- 2}{O}

In PbO₂, Pb is in +4 oxidation state. Due to inert pair effect Pb in +2 oxidation state is more stable. So, Pb in +4 oxidation state (PbO₂) acts as an oxidising agent.

It oxidises Cl^- to Cl₂ and itself gets reduced to Pb²⁺.

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