Question

Carbon cannot be used to reduce $A{l_2}{O_3}$ to Al while ZnO can be reduced by carbon. If it is true, then enter 1, else enter 0.

Answer 1

Hint: The ability of reducing alumina and zinc oxide depends upon the affinity of oxygen atoms towards carbon atoms. If affinity of carbon and oxygen atoms is more than affinity between the metal atom and oxygen, then carbon will reduce the metal from its oxide.

Complete step by step solution:
We will know whether carbon can reduce $A{l_2}{O_3}$ and ZnO or not.
- We know that carbon has oxidation number zero and can act as an oxidizing agent for such reactions.
- However, $A{l_2}{O_3}$ has aluminum in oxidation number +3. Reduction of alumina by carbon is not done because of some reasons.
- The reduction reaction of alumina by carbon requires very high temperatures like 2100 $^ \circ C$. Alongside this, aluminum has more affinity towards oxygen atoms than the carbon atoms have towards oxygen. At very high temperature, actually this reaction proceeds but it requires very high amounts of heat.
- The affinity for oxygen atoms is high in case of carbon as compared to Zinc. Thus, carbon can be used to reduce zinc from zinc oxide. The reaction can be written as below.
\[2ZnO + C \to 2Zn + C{O_2}\]
- The free energy change of the reaction is negative. So, this reaction is thermodynamically feasible. Zn metal is in +2 oxidation state in ZnO and it gets reduced to zero oxidation state. Carbon atoms get oxidized from zero to +4 oxidation state.

- Thus, we can say that the statement given in the question is true. So, we will enter 1.

Note: The reagent which is used to oxidize compounds is called oxidizing agent and it itself undergoes reduction reaction. Reducing agents are used to reduce other compounds and itself undergoes oxidation reactions.