Rajasthan BoardEnglish MediumSTD 12 ScienceChemistryElectro Chemistry5 Marks
Question
Discuss electrochemical principle regarding rusting of iron.
✓
Answer
Electrochemical Principle: It can be explained by taking the example of formation of rust. The water vapour present on the surface of metal dissolved $CO _2$ and $O _2$ to form carbonic acid. $H _2 O + CO _2 \longrightarrow H _2 CO _3, H _2 CO _3$ act as electrolytic solution and ionise $H _2 CO _3 \longrightarrow 2 H ^{+}+ CO _3^{2-}$ $\Rightarrow \quad H _2 O \longrightarrow H ^{+}+ OH ^{-}$ Iron in contact with water gets oxidise to $Fe ^{2+}$ $Fe \longrightarrow Fe ^{2+}+2 e^{-}\left( E _{ Fe ^{2+}}^0 Fe =-0.44 V\right)$ The above reaction takes places at a place which act as anode. Electrons lost by iron are taken by $H ^{+}$ions. It react with oxygen to form water. $4 H ^{+}+ O _2 \longrightarrow 2 H _2 O$ Overall reaction is $4 H ^{+}+ O _2+4 e^{-} \longrightarrow 2 H _2 O$ The sites where these reaction's take place act on cathodes. The overall cell reaction can we written, $2 Fe +4 H ^{+}+ O _2 \longrightarrow 2 Fe ^{2+}+2 H _2 O \quad\left[ E _{\text {cell }}=1.67 V\right]$ $Fe ^{2+}$ ions get oxidise by atmospheric oxygen into $Fe ^{3+}$ which react with water to form rust. $4 Fe ^{2+}+ O _2+4 H _2 O \longrightarrow 2 Fe _2 O _3+8 H ^{+}$ $\Rightarrow \quad Fe _2 O _3+x H _2 O \longrightarrow Fe _2 O _3 . x H _2 O$ rust (hydrated ferric oxide)
Need a full question paper?
Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.