Isolation of Elements

Copper pyrites	:	CuFeS2
Malachite	:	CuCO3 . Cu(OH)2
Azurite	:	2CuCO3 . Cu(OH)2
Dolomite	:	CaCO3 . MgCO3

2Cu₂S  +  3O₂   $ \to $   2Cu₂O  +   2SO₂

2Cu₂O  +  Cu₂S  $ \to $  6Cu  +  SO₂

It is a example of auto reduction.

First a part of sulphide ore is converted into oxide which then reacts with remaining sulphide to give the metal.

The gangue material in the ore is removed by adding another chemical substance called flux. If ore has basic impurities, such as FeO, CaO, MgO, etc. suitable acid flux such as SiO₂ , P₂O₅ , etc. are used. For example, in the extraction of copper, ferrous oxide (FeO), a basic impurity, is removed by adding silica. FeO (gangue) and SiO₂ (flux) together form slag FeSiO₃.

Froth floatation method is mainly applicable for sulphide ores.

$(1)$ Malachite ore : $Cu{\left( {OH} \right)_2},\,\,CuC{O_3}$

$(2)$ Magnetite ore : $F{e_3}{O_4}$

$(3)$ Siderite ore : $FeC{O_3}$

$(4)$ Galena ore : $PbS$ (Sulphide Ore)

In the metallurgy of aluminium purified $A{l_2}{O_3}$ is mixed with $N{a_3}Al{F_6}\,\,$ $\,\,\,$ or $\,\,\,$ $Ca{F_2}$ which lowers the melting point of the mix and brings conductivity.

Van Arkel is a method in which heat treatment it used to purify metal in this process metals are converted into other metal compound for loosly coupled like as iodine to make metal iodide which are easily decomposed and give pure metal.

The process is known as Van Arkel method.

NOTE : The reduction of metal sulphides by carbon reduction process is not spontaneous because $\Delta G$ for such a process is positive. The reduction of metal oxide by carbon reduction process is spontaneous as $\Delta G$ for such a process is negative.

From this we find that on thermodynamic considerations $C{O_2}$ is more stable than $C{S_2}$ and the metal sulphides are more stable than corresponding oxides.

In view of above the factor listed in choice (c) is incorrect and so is of no significance.

Hence the correct answer is $(c)$

During the process of electrolytic refining Ag and Au are obtained as anode mud.

NOTE : Galena is PbS and thus purified by froth floatation method.

Froath floatation method is used to concentrate sulphide ores. This method is based on the preferential wetting properties with the froathing agent and water.

Silver ore forms a soluble complex with $NaCN$ from which silver is precipitated using scrap zinc.

$A{g_2}S + 2NaCN \to $

$\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,Na\left[ {Ag{{\left( {CN} \right)}_2}} \right]\buildrel {Zn} \over \longrightarrow $

$\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,N{a_2}\left[ {Zn{{\left( {CN} \right)}_4}} \right] + Ag \downarrow $

$\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,$sodargento-cynanide(soluble)

Pure aluminium can be obtained by electrolysis of a mixture containing alumina, crayolite and fluorspar in the ratio $20:24:20.$ The fusion temperature of this mixture is ${900^ \circ }C$ and it is a good conductor of electricity.