Question

Which of the following reactions is an example of auto reduction?
A.$F{e_3}{O_4} + 4CO \to 3Fe + 4C{O_2}$
B.$CuO + C \to 2Cu + CO$
C.$C{u^{2 + }}_{\left( {aq} \right)} + F{e_{\left( s \right)}} \to C{u_{\left( s \right)}} + F{e^{2 + }}_{\left( {aq} \right)}$
D.$C{u_2}O + \dfrac{1}{2}C{u_2}S \to 2Cu + \dfrac{1}{2}S{O_2}$

Answer 1

Hint:We can say Auto reduction is a largely used industrial process of extraction of metal from minerals (or) ores that too for less electropositive metals such as copper, lead and mercury etc.

Complete step by step answer:
We can say auto reduction is a reaction in metallurgy. It is a process in which sulphide ores of less electropositive metals such as Hg, Pb, Cu etc., are heated in air and a part of the ore is converted into oxide or sulphate which reacts with the rest of sulphide ore in absence of air to form the metal and sulphur dioxide.
Therefore in simple words, we could say that the auto reduction process is used in the synthesis of less electropositive metals such as copper, mercury, lead etc.
In the process of copper ore extraction, the partial roasting of sulfide ore of copper gives its oxide. After some time, when the supply of air is stopped, and with the increase in temperature the rest of sulfide ore is converted into metal.
We can give the chemical equations as,
$2C{u_2}S + 3{O_2} \to 2CuO + 2S{O_2}$
$C{u_2}O + \dfrac{1}{2}C{u_2}S \to 2Cu + \dfrac{1}{2}S{O_2}$
Therefore, option (D) is correct.
Iron does not fall in the category, which means we cannot obtain iron from its ore by the process of auto reduction. So, the auto reduction process is not used in the metallurgy of iron. Therefore, option (A) is incorrect.
The reaction $CuO + C \to 2Cu + CO$ is a redox reaction. Therefore option (B) is incorrect.
The reaction $C{u^{2 + }}_{\left( {aq} \right)} + F{e_{\left( s \right)}} \to C{u_{\left( s \right)}} + F{e^{2 + }}_{\left( {aq} \right)}$ is a redox reaction. Therefore option (C) is incorrect.

The correct option is D.

Note:
We have to know in the process of metallurgy to obtain metals from its ore, there isn’t any use of an external reducing agent that is why we call the process an auto-reduction process. The other name for this process is air reduction since in this process there are two steps involved. In the first use, the reaction is carried in the presence of air, and in the second step, the reaction is carried in absence of air. So in this way, the decrease in supply of air happens.