1. Give an example of extraction based on oxidation
reduction.
Ans 1. An example based on extraction by
oxidation is extraction of chlorine from brine.
2. How are gold and silver extracted?
Ans 2. Gold and silver are extracted by
leaching the metal with CN- . The metal is later recovered by displacement
method in which zinc acts as reducing agent.
3Give two examples of metal refined by a) Distillation b) Liquation c) Electrolytic
refining
Ans 3. a) Distillation – Zinc and Mercury b)
Liquation – Tin and Antimony c) Electrolytic refining – Copper and Zinc.
4.Which method is used for refining of silicon or
gallium?
Ans 4. The refining of Silicon or gallium is
done by Zone refining
5.What is the principle behind zone refining?
Ans 5. The principle of zone refining is that
impurities are more soluble in the melt then in the solid state of the metal.
Ans.6. The two requirements of vapour phase
refining are :- 1) The metal should from a volatile compound with an available
reagent, 2) The volatile compound should be easily decomposable so that
recovery is easy.
7. Which method is used for refining of zirconium? Explain.
Ans.7. Zirconium and Titanium are refined by van Ankle
process, Here the crude metal is heated in an evacuated vessel with iodine. Zr+ 2 I2 + → ZrI4 The metal iodide is decomposed on a tungsten filament,
electrically heated to about 1800K and pure metal is deposited on the filament.
ZrI4 → Zr +2I2.
8.What is the principle behind chromatography? Name some
types of chromatographic techniques.
Ans 8. The principle behind chromatography is that different
components of a mixture are differently adsorbed on an adsorbent. Some of the
chromatographic techniques are paper chromatography, column chromatography, gas
chromatography etc.
9. What is pig iron?
Ans 9. The iron which is obtained from blast furnace and contains about 4% carbon
and many other impurities in smaller amounts like S, P, Si, Mn etc, is called
pig iron.
10 What is cast iron?
Ans 10. Iron obtained by melting pig iron
with scrap iron and coke using hot air blast is cast iron.
Ans 11. Wrought iron and malleable iron is
the purest form of commercial iron which is prepared from cast iron by
oxidizing impurities in a reverberatory furnace lined with heamatite.
12 What is added as flux in extraction of iron?
Ans 12. Limestone is used as flux in
extraction of iron.
13 Explain the extraction of copper?
Ans 13. The sulphide ores of copper are
roasted to give oxides: 2Cu2S + 3O2→2Cu2O + 2SO2.
The oxide can then
be easily reduced to metallic copper using coke.
2 Cu O +C → 2Cu+CO
The
impurities like iron oxide are removed as slag by reacting with SiO2, added as
flux.
FeO + SiO2 + → FeSiO3.
14. What is Blister copper?
Ans 14. The solidified copper obtained after
extraction has blistered appearance due to evolution of SO2 is called blister
copper.
15What is the basis of reduction of a molten metal
salt? Explain ?
Ans.15 In the reduction of molten metal
salt, electrolysis is done which is based on electrochemical principles
following equation∆G 0 = − nFE Here n is the number of electrons and E0 is
the electrode potential of redox couple. More reactive metals have large
negative values of the electrode potential and are difficult to reduce.
16. Why is cryolite used during extraction of
Aluminum?
Ans.16Cryolite is used to lower the melting
point of alumina and increase conductivity.
17. How is copper extracted from low grade ores?
Ans17. Copper is extracted by
hydrometallurgy from low grade ores. It is leached out using acid or bacteria.
18.Define the term - metallurgy?
Ans. The scientific and technological process
used for isolation of the metal from its ores is known as metallurgy.
19. What
is gangue?
Ans. The earthly or undesired materials
which contaminate ore are called gangue.
20.Give some important ores of Aluminum, Iron,
Copper and Zinc?
Ans. Metal Ore
Aluminum -Bauxite
Iron- Hematite, Magnetite
Copper -Copper pyrite, Copper glance
Zinc -Zinc blende, Calamine
21.What is the basis of hydraulic washing? For
which type of ores is it used?
Ans. Hydraulic washing is based on the differences
in the gravities of the ore and the gangue particles. It is used when ore is
heavy and impurities are lighter.
22.. Explain froth floatation method.
Ans. Froth floatation is used for removing
gangue from sulphide ores. Here a suspension of the powdered ore is mixed with
water. To it collectors and froth stabilizer are added. A rotating paddle
agitates the mixture and draws air in it. As a result froth is formed. The
mineral particles become wet by froth (oil) and gangue particles by water. The
froth is skimmed off and dried for the recovery of ore.
23. What is the role of a depressant in the
floatation process? Give an example?
Ans. Depressant adjusts the proportion of
oil and water so as to separate two sulphide ores. e.g. in case of an ore
containing ZnS and PbS, NaCN is used an depressant which selectively prevents
ZnS from coming to the froth.
24. What is used as collectors and froth
stabilizers in froth floatation process? What is their role in the process?
Ans . Pine oil, fatty acids or xanthate can
be used as collectors to enhance the non- wettability of mineral particles
whereas cresols or aniline can be used as froth stabilizer to stabilize the
froth in froth floatation process.
25. . What is leaching? Explain with an example.
Ans . Leaching is used if the ore is
soluble in suitable solvent. e.g. Aluminum is leached from bauxite by using a
conc. solution of NaOH at 473-523 K and 35-36 bar pressure. Al2O3 is leached
out an sodium aluminates leaving behind impurities-
Al2O3 (S) + 2NaOH(aq)+3H2O → 2Na[Al(OH)4 ]
The aluminate solution is centralised by passing CO2 gas &
hydrated Al2O3 is precipitated which is filtered, dried and heated to give pure
Al2O3.
2Na[Al(OH)4 ] + CO2→ + 2NaHCO3(aq)
Al2O3.xH2O(s) → Al2O3(s) + xH2O(g).
26. Which reagent is used for leaching of Gold
or silver? Write the equations involved.
Ans.A dil. Solution of NaCN or KCN in the
presence of air is used as reagent for leaching of silver and gold. The
equations are
4M(s) + 8CN-(aq) +2H2O(aq) + O2(g)
-------------- 4[Mn(CN)2]-(aq) + 4OH-(aq)
2[M(CN)2]-(aq) + Zn(s) --------------
[Zn(CN)4]-2(aq) + 2M(s).
27. What are Ellingham diagrams?State one limitation of Ellingham diagrams.
Ans. Ellingham diagrams are graphical representation of variation of ∆ G vs T for the
formation of oxides of elements i.e., for the reaction
2xM(s) +O2(g) →2MxO(g). Ellingham diagrams only tell us about the feasibility of a reaction. They do not tell
anything about the reaction kinetics.
28. Write the relationship between Gibbs free energy, enthalpy change
and change in entropy?
Ans. When ∆ S is entropy change , ∆H is enthalpy change , than at temperature T, the
change is Gibbs free energy is given by
∆ G = ∆H – T∆ S.
29.What is the condition for a reduction reaction to occur in terms of free
energy change? How can it be achieved?
Ans. When the value of ∆ G is negative , the reduction reaction is said to be spontaneous
1) It ∆ S is positive , on increasing the temperature, the value of T∆ S would increase
& ∆ G will become negative.
2) For a process which is otherwise having ∆ G positive & is non- spontaneous, , it can
be coupled with a reaction having highly negative ∆ G value so that the overall ∆ G
is negative and the process can take place.
30. Sulphide and carbonate ores are converted to oxide before reduction. Why?
Ans. Since the reduction of oxide ores involves a decrease in Gibb’s free energy making ∆ G
value more negative, it is easier to reduce oxides therefore suphide and carbonate ores
are converted to oxides before reduction.
