Question

In order to refine blister copper, it is melted in a furnace and is stirred with green logs of wood. The purpose is:
A. To expel the dissolved gases in blister copper.
B. To reduce the metallic oxide impurities with hydrocarbon gases liberated from the wood.
C. To bring the impurities to the surface and oxidize them.
D. To increase the carbon content in copper.

Answer 1

To avoid removing too much of the oxygen from the anode, as this will cause other impurities to change from their oxide to metallic states. For the extraction of copper from the sulphide ores, the process of smelting is used. Blister copper is the purest form of copper after electrically refined copper.

Complete answer:

In the process of copper extraction, copper matte which is a combination of copper sulphide and iron sulphide is extracted before the final step, which on reduction forms blister copper.
The blister copper is melted in a reverberatory furnace and stirred with poles of greenwood. Any oxide of copper formed is reduced to metallic copper by the reducing hydrocarbons of the wood. The process is called fire refining or poling.
At very high temperatures, the Sulphur is removed as Sulphur dioxide by blowing air through the molten matter.
$2Cus + 3{O_2} \to 2Cu{O_2} + 2S{O_2}$
In this process, green logs of wood act as a reducing agent to reduce copper oxide to metal.
$3Cu{O_2} + C{H_4}(from\;{{ }}\;green{{ }}\;log s{{ }}\;of{{ }}\;woods) \to 6Cu + 2{H_2}O + CO$
The heat of the copper makes the pole emit wood gas(CO2 and H2) that reduces the cuprous oxide to copper.

So, the correct answer is Option B.

Note: Blister copper contains $Cu_2O$ as an impurity and is refined by the poling process. It was the use of these greenwood poles that gave rise to the term “poling”. Poling is the process of reducing oxides by adding green logs of wood.