Question

Sometimes roasting may not bring about complete oxidation:
$\text{ 2CuFe}{{\text{S}}_{\text{2}}}\text{+ 4}{{\text{O}}_{\text{2}}}\to \text{ A + 2FeO + 3S}{{\text{O}}_{\text{2}}}\text{ }$
Find out A:
(A) $\text{C}{{\text{u}}_{\text{2}}}\text{O}$
(B) $\text{CuO}$
(C) $\text{C}{{\text{u}}_{\text{2}}}\text{S}$
(D) $\text{CuS}$

Answer 1

Hint: The roasting is a process of heating ore strongly in presence of an excess of the air at a temperature below the melting point of the metal. The copper is extracted from the copper pyrites. The copper pyrite is an ore of copper and ferrous. On oxidation, the copper from the copper pyrite first breaks down into ferrous sulphide and cuprous sulphide. On further oxidation, ferrous sulphide converts into the\[\text{FeO}\].

Complete step by step answer:
We know that roasting is a metallurgical process. In presence of an excess of air, the ore (mostly sulphide ores) is heated strongly is called roasting. The melting point of the ore should be higher than the heating temperature.
This method is mainly employed in the case of the sulphide ores. As a result of roasting, the moisture and volatile impurities are removed and the ore is converted to oxide. For example, impurities of sulphur, arsenic, and phosphorous are, removed as their volatile oxides $\text{ S}{{\text{O}}_{\text{2}}}$ ,$\text{ A}{{\text{s}}_{\text{2}}}{{\text{O}}_{\text{3}}}\text{ }$, $\text{ }{{\text{P}}_{\text{2}}}{{\text{O}}_{\text{5}}}\text{ }$, respectively.
For example,
$\text{ }{{\text{S}}_{\text{8}}}\text{ + 8}{{\text{O}}_{\text{2}}}\text{ }\to \text{ 8S}{{\text{O}}_{\text{2}}}\text{ }\uparrow $
We are given the reaction as,
$\text{ 2CuFe}{{\text{S}}_{\text{2}}}\text{+ 4}{{\text{O}}_{\text{2}}}\to \text{A + 2FeO + 3S}{{\text{O}}_{\text{2}}}\text{ }$
In the reaction, we are interested to determine the A.

The copper is extracted from the copper pyrites$\text{CuFe}{{\text{S}}_{\text{2}}}$. It is a sulphide ore of copper. The copper pyrite is roasted that is heated strongly in presence of an excess of air in a reverberatory furnace. In the furnace, the copper is converted to the ferrous sulphide$\text{ (FeS) }$, cuprous sulphide$\text{ (C}{{\text{u}}_{\text{2}}}\text{S) }$which is partially oxidized.
The reaction is as depicted below:
 $\text{ 2CuFe}{{\text{S}}_{\text{2}}}\text{ + 4}{{\text{O}}_{\text{2}}}\to \text{C}{{\text{u}}_{\text{2}}}\text{S + 2FeS + S}{{\text{O}}_{\text{2}}}\text{ }$ (1)

The ferrous sulphide $\text{ (FeS) }$further undergoes the oxidation to produce the ferric oxide$\text{ (FeO) }$. The reaction is as follows:
\[\text{ 2FeS + 3}{{\text{O}}_{\text{2}}}\text{ }\to \text{ 2FeO + 2S}{{\text{O}}_{\text{2}}}\text{ }\] (2)
On combining (1) and (2) reaction we get:
$\text{ 2CuFe}{{\text{S}}_{\text{2}}}\text{ + 4}{{\text{O}}_{\text{2}}}\to \text{C}{{\text{u}}_{\text{2}}}\text{S + 2FeO + 3S}{{\text{O}}_{\text{2}}}\text{ }$ (3)
On comparing the reaction (3) with the given reaction, the A is equal to the$\text{ C}{{\text{u}}_{\text{2}}}\text{S }$.
So, the correct answer is “Option C”.

Additional Information:
The process of heating the sulphide ores at a high temperature in presence of air is called roasting. It is the main step in the extraction of ore.
This process is very useful but it causes air pollution. In the case of roasting of sulphide ore, sulphide will be converted to an oxide, and sulphur is released as sulphur dioxide gas.
The sulphur dioxide formed from the roasting of sulphide ores is used for the preparation of sulphuric acid through the contact process.

Note: Roasting is the process of conversion of ore into the metallic oxides in presence of an excess of air. However, the calcination is the process of converting ore into its metallic oxide either in the absence or in the limited supply of air.
Here, the ore essentially breaks down in the metal sulphides. Partially oxidation reduces the chances of unwanted oxidation of the metal or the second metal in the ore.