Silicon is purified by zone refining . Metals of high purity are always purified by zone refining.
2.
Four metals and their methods of refinement are given
(i) $$Ni,Cu,Zr,Ga$$
(ii) electrolysis, van Arkel process, zone refining Mond's process
Choose the right method for each
A.
$$Ni :$$ Electrolysis, $$Cu :$$ van Arkel process, $$Zr :$$ Zone refining, $$Ga :$$ Mond's process
B.
$$Ni :$$ Mond's process, $$Cu :$$ Electrolysis, $$Zr :$$ van Arkel process, $$Ga :$$ Zone refining
C.
$$Ni :$$ Mond's process, $$Cu :$$ van Arkel process, $$Zr :$$ Zone refining, $$Ga :$$ Electrolysis
D.
$$Ni :$$ Electrolysis, $$Cu :$$ Zone refining, $$Zr :$$ van Arkel process, $$Ga :$$ Mond's process
Answer :
$$Ni :$$ Mond's process, $$Cu :$$ Electrolysis, $$Zr :$$ van Arkel process, $$Ga :$$ Zone refining
The sulphide ores of certain less electropositive metals like those of $$Hg,Pb,Cu,$$ etc. when heated in air bring about the conversion of a part of the sulphide ore to oxide or sulphate which then reacts with the remaining sulphide to give the metal and $$S{O_2}.$$ No external reducing agent is used in this process.
$$\eqalign{
& 2C{u_2}S + 3{O_2} \to 2C{u_2}O + 2S{O_2} \cr
& 2C{u_2}O + C{u_2}S \to 6Cu + S{O_2} \cr} $$
5.
Which one of the following is a mineral of iron?
$$\eqalign{
& {\text{Mineral}}\,\,\,\,\,\,\,\,\,\,\,{\text{Chemical}}\,\,{\text{composition}} \cr
& {\text{Malachite}}\,\,\,\,\,\,\,\,CuC{O_3}.Cu{\left( {OH} \right)_2} \cr
& {\text{Cassiterite}}\,\,\,\,\,\,\,\,Sn{O_2} \cr
& {\text{Pyrolusite}}\,\,\,\,\,\,\,\,Mn{O_2} \cr
& {\text{Magnetite}}\,\,\,\,\,\,\,\,Fe{O_4} \cr
& {\text{Thus, magnetite is a mineral of iron}}{\text{.}} \cr} $$
6.
Which of the following statements regarding metallurgy of iron is incorrect ?
A.
Reaction $$F{e_3}{O_4} + 4CO \to 3Fe + 4C{O_2}$$ belongs to lower temperature range $$(500 – 800K)$$ of the blast furnace.
B.
Reaction $$FeO + CO \to Fe + C{O_2}$$ belongs to higher temperature range $$(900 – 1500K)$$ of the blast furnace.
C.
The iron obtained from blast furnace is cast iron with $$3\% $$ carbon.
D.
For reduction of iron oxide to occur $$\Delta G$$ of the couple of following reactions should be negative
$$\eqalign{
& FeO\left( s \right) \to Fe\left( s \right) + \frac{1}{2}{O_2}\left( g \right) \cr
& C\left( s \right) + \frac{1}{2}{O_2}\left( g \right) \to CO\left( g \right) \cr} $$
Answer :
The iron obtained from blast furnace is cast iron with $$3\% $$ carbon.
The free energy of formation $$\left( {\Delta {G^ \circ }} \right)$$ of $$CO$$ from $$C$$ becomes lower at temperatures above $$1180\,K$$ whereas that of $$C{O_2}$$ from $$C$$ becomes lower above $$1270\,K$$ than $${\Delta {G^ \circ }}$$ of $$ZnO.$$ However, $${\Delta {G^ \circ }}$$ of $$C{O_2}$$ from $$CO$$ is always higher than that of $$ZnO.$$ Hence, $$C$$ can reduce $$ZnO$$ to $$Zn$$ but not $$CO.$$