Question

Extraction of zinc from zinc blende is achieved by:
A.electrolytic reduction
B.roasting followed by reduction with carbon
C.roasting followed by reduction with another metal
D.roasting followed by self reduction

Answer 1

Hint: Zinc from zinc blende is obtained by first roasting of zinc. After roasting, a reduction process is carried out in the presence of carbon which leads to the formation of free metal that is zinc.

Step-by-step answer:
The molecular formula of zinc blend is ZnS. Zinc blende is an ore. Any metal can be extracted by following two major steps:
Conversion of the ore into metallic oxide.
Reduction of the metallic oxide to the free metal.

In order to get zinc from zinc blende (ZnS), first the conversion of zinc blende (ore) to zinc oxide (metallic oxide) is carried out. The conversion of ore to metallic oxide can be done by calcination and roasting.

Calcination is generally utilized to convert hydrated oxides or hydroxides and carbonates into respective oxides while roasting is generally utilized to convert sulphide ores to respective oxides.

Zinc blende (ZnS) is a sulphide ore. Thus the roasting process will be carried out to first convert zinc blend to zinc oxide (ZnO). The reaction is as follows:

$$2{\text{ZnS}} + 3{{\text{O}}_{\text{2}}} \to 2{\text{ZnO}} + {\text{2S}}{{\text{O}}_2}$$

Now, reduction of the metallic oxide to the free metal is carried out. The reduction of zinc oxide in the presence of carbon leads to the formation of zinc metal.

$${\text{ZnO}} + {\text{C}} \to {\text{Zn}} + {\text{CO}}$$

Thus the correct option is B.

Note: Always remember that for the conversion of sulphide ore (such as PbS) to metallic oxides, roasting process is carried out while for the conversion of hydrates oxide (such as $${\text{A}}{{\text{l}}_{\text{2}}}{{\text{O}}_{\text{3}}} \cdot 2{{\text{H}}_{\text{2}}}{\text{O}}$$) and carbonates $$\left( {{\text{CaC}}{{\text{O}}_{\text{3}}}} \right)$$ to metallic oxides, calcination process is carried out. After this, the conversion of metallic to free metal is done by reduction with carbon.