11.
Fill in the blanks with the correct choice.
The undesired impurities present in the ores are called $$\underline {\left( {\text{i}} \right)} .$$ To remove the volatile impurities from the ore, the $$\underline {\left( {{\text{ii}}} \right)} $$ process is carried out. Flux combines with non-fusible impurities to form $$\underline {\left( {{\text{iii}}} \right)} .$$ $$CaO$$ acts as a $$\underline {\left( {{\text{iv}}} \right)} $$ flux.
Extraction of $$Zn$$ from zinc blends is achieved by roasting followed by reduction with carbon. Reactions involved are :
\[\begin{align}
& 2ZnS+3{{O}_{2}}\xrightarrow{\text{heat}}2ZnO+2S{{O}_{2}}\text{(Roasting)} \\
& ZnO+C\text{(Coke)}\xrightarrow{\text{heat}}Zn+CO\text{(Reduction)} \\
\end{align}\]
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.
15.
Find the incorrect match.
A
Fine dust of aluminium - Paints and Lacquers
B
Reducing agent in the manufacture of dye-stuffs, paints, etc. - Copper dust
C
For cutting tools and crushing machines - Chrome steel
D
For making cables, automobiles and aeroplane parts - Nickel steel
Answer :
Reducing agent in the manufacture of dye-stuffs, paints, etc. - Copper dust
In electro-refining of copper, the zinc, nickel and iron remain in the solution, while gold is deposited as anode mud. The anode decreases in weight gradually.
18.
Which of the following metals is extracted by the electrometallurgical method ?
$$A - 4,\,B - 2,\,C - 3,\,D - 1$$
$$ \bullet $$ Cyanide process It is a metallurgical technique for extracting $$Au$$ (gold) from low grade ore by corverting the $$Au$$ to a water-soluble coordination complex.
$$ \bullet $$ Froth floatation process This process is used for dressing of sulphide ore, i.e. $$ZnS.$$
$$ \bullet $$ Electrolytic reduction This process is used for extraction of $$Al$$ which is carried out in a steel tank lined inside with graphite. Here, graphite serves as cathode. The electrolyte consists of alumina dissolved in fused cryolite $$\left( {N{a_3}Al{F_6}} \right)$$ and fluorspar $$\left( {Ca{F_2}} \right).$$
$$ \bullet $$ Zone refining This process is used for ultra pure $$Ge$$ element. An ingot of $$Ge$$ is first purified by zone refining. Then a small amount of antimony is placed in the molten zone which is passed through the pure $$Ge$$ with the proper choice of rate of heating and other variables.