Question

Blister copper is refined by stirring molten impure metal with green logs of wood because such a wood liberate hydrocarbon gases (like$\text{C}{{\text{H}}_{\text{4}}}$). This process X is called-----and the metal contains impurities of Y is -----
(A) X = cupellation Y =$\text{Cu}{{\text{O}}_{\text{2}}}$
(B) X = polling Y =$\text{C}{{\text{u}}_{\text{2}}}\text{O}$
(C) X = polling Y = $\text{CuO}$
(D) X = cupellation Y = $\text{CuO}$

Answer 1

Hint: Polling is used for the purification of that metal which contains their own oxide as an impurity. Blister copper contains 90% copper and 2% impurities of sulphur and iron oxide and its surface appears as bubbles or blisters on the surface of the metal.

Complete answer:
Polling is used to purify blister copper and it mainly contains the metal oxide ($\text{CuO}$) as an impurity. This process is used for the metal having the impurity of the same metal oxide. In this process a wooden pole is heated with molten metal, which provides carbon and hydrogen to metal oxide which reduces impurity of metal oxide to metal.
\[\begin{align}
& \text{CuO}\,\,\text{+}\,\,{{\text{H}}_{\text{2}}}\,\to \,\,\text{Cu}\,\,\text{+}\,\,{{\text{H}}_{\text{2}}}\text{O} \\
& \text{CuO}\,\,\text{+}\,\,\text{C}\,\,\to \,\,\text{Cu}\,\,\text{+}\,\,\text{CO} \\
\end{align}\]
In this process a green long wood stick is used to stir the liquid metal. Metal is reduced by the hydrocarbon of wood and \[{{\text{O}}_{\text{2}}}\] leaves as \[\text{C}{{\text{O}}_{\text{2}}}\] gas. The impure copper metal is refined in two stages – oxidation and reduction.
In oxidation stage like \[\text{S}{{\text{O}}_{\text{2}}}\] and \[\text{FeO}\] is removed by the by aeration over the metal surface. For reduction, reducing agents like natural gases and ammonia are used to reduce copper oxide to copper metal. In the old days for the reduction process green wood was used as poles. Heating of plant hydrocarbon releases \[\text{C}{{\text{O}}_{\text{2}}}\] and \[{{\text{H}}_{\text{2}}}\] gas and these gases will reduce copper oxide to copper.

So, option (C) is the correct option.

Note: To prevent the further oxidation pure metal the upper surface should be covered with coke. Removal of a large amount of oxygen gas from anode copper causes conversion of its oxides to metallic form and it will remain in impure copper metal in solid solution.