Question

Which of the following reaction is an example of auto reduction?

• A. $\mathrm { Fe } _ { 3 } \mathrm { O } _ { 4 } + 4 \mathrm { CO } \longrightarrow 3 \mathrm { Fe } + 4 \mathrm { CO } _ { 2 }$
• B. $\mathrm { Cu } _ { 2 } \mathrm { O } + \mathrm { C } \longrightarrow 2 \mathrm { Cu } + \mathrm { CO }$
• C. $\mathrm { Cu } ^ { 2 + } { } _ { ( \mathrm { aq } ) } + \mathrm { Fe } _ { ( \mathrm { s } ) } \longrightarrow \mathrm { Cu } _ { ( \mathrm { s } ) } + \mathrm { Fe } ^ { 2 + } { } _ { ( \mathrm { aq } ) }$
• D. $\mathrm { Cu } _ { 2 } \mathrm { O } + \frac { 1 } { 2 } \mathrm { Cu } _ { 2 } \mathrm {~S} \longrightarrow 3 \mathrm { Cu } + \frac { 1 } { 2 } \mathrm { SO } _ { 2 }$

Answer 1

Answer: (D)

$\mathrm { Cu } _ { 2 } \mathrm { O } + \frac { 1 } { 2 } \mathrm { Cu } _ { 2 } \mathrm {~S} \longrightarrow 3 \mathrm { Cu } + \frac { 1 } { 2 } \mathrm { SO } _ { 2 }$

Answer 2

The sulphide ores of certain less electropositive metals like those of Hg, Pb, Cu, etc. when heated in air bring about the conversion of a part of the sulphide ore to oxide or sulphate which then reacts with the remaining sulphide to give the metal and $\mathrm { SO } _ { 2 }$ No external reducing agent is used is this process.

$2 \mathrm { Cu } _ { 2 } \mathrm {~S} + 3 \mathrm { O } _ { 2 } \rightarrow 2 \mathrm { Cu } _ { 2 } \mathrm { O } + 2 \mathrm { SO } _ { 2 }$

$2 \mathrm { Cu } _ { 2 } \mathrm { O } + \mathrm { Cu } _ { 2 } \mathrm {~S} \rightarrow 6 \mathrm { Cu } + \mathrm { SO } _ { 2 }$