Question

# The chemical formula for copper pyrites is:(A)- $CuFe{{S}_{2}}$ (B)- $C{{u}_{2}}S$ (C)- $C{{u}_{2}}O$ (D)- $CuC{{O}_{3}}.Cu{{(OH)}_{2}}$

Hint: Pyrite is the most abundantly found sulphide mineral and also known as iron pyrite. Most of the copper ores occur in nature as sulphides. Copper pyrite is an important ore of copper. It is known commonly as chalcopyrite.

Pyrite or iron pyrite is a sulphide ore of iron and has the chemical formula $Fe{{S}_{2}}$.
From the above given options, we can rule out $CuC{{O}_{3}}.Cu{{(OH)}_{2}}$ and $C{{u}_{2}}O$, since these compounds are not sulphides.
$C{{u}_{2}}S$ is copper sulphide and is not a pyrite mineral.
So, we are now only left with $CuFe{{S}_{2}}$.
Copper pyrite is copper iron sulphide and its chemical formula is given as $CuFe{{S}_{2}}$.
So, the correct answer is “Option A”.

Copper metal is extracted from copper pyrite. Copper iron sulphide ($CuFe{{S}_{2}}$) is first concentrated by the froth flotation process and then is roasted (i.e. heating in excess of oxygen) in a reverberatory furnace. On roasting, copper pyrite gives a mixture of iron sulphide or ferrous sulphide (FeS) and cuprous sulphide ($C{{u}_{2}}S$).
$2CuFe{{S}_{2}}+{{O}_{2}}\to C{{u}_{2}}S+2FeS+S{{O}_{2}}$
$2FeS+3{{O}_{2}}\to 2FeO+2S{{O}_{2}}$
Copper is less reactive than iron, thus, and cuprous sulphide is not oxidized into copper oxide ($C{{u}_{2}}O$). If any $C{{u}_{2}}O$ is formed, FeS reacts with it and converts it back into $C{{u}_{2}}S$, i.e.
\begin{align} & 2{{C}_{2}}S+3{{O}_{2}}\to 2C{{u}_{2}}O+2S{{O}_{2}} \\ & C{{u}_{2}}O+FeS\to C{{u}_{2}}S+FeO \\ \end{align}
FeS and $C{{u}_{2}}S$ are then mixed with silica ($Si{{O}_{2}}$) and heated in a furnace. FeO reacts with $Si{{O}_{2}}$ to form ferrous silicate ($FeSi{{O}_{3}}$). $FeSi{{O}_{3}}$ is called slag and being lighter floats above the molten layer of $C{{u}_{2}}S$ and unreacted FeS, which is known as copper mate. Then, copper is obtained from copper matte.
Note: Always keep in mind that pyrite has the chemical formula $Fe{{S}_{2}}$. It is an iron sulphide. $CuFe{{S}_{2}}$ is copper iron sulphide whereas $C{{u}_{2}}S$ is a simple sulphide of copper. So do not confuse between $C{{u}_{2}}S$ and $CuFe{{S}_{2}}$ for the correct answer.