12th Chemistry Guide Metallurgy Text Book Questions and Answers
I. Choose the correct answer
1. Bauxite has the composition
- a) Al2O3
- b) Al2O3.nH2O ✓ Correct
- c) Fe2O3.2H2O
- d) None of these
Answer: b) Al2O3.nH2O
2. Roasting of sulphide ore gives the gas (A). (A) is a colorless gas. An aqueous solution of (A) is acidic. The gas (A) is
- a) CO2
- b) SO3
- c) SO2 ✓ Correct
- d) H2S
Answer: c) SO2
3. Which one of the following reaction represents calcinations?
- a) $2Zn+O_{2}\rightarrow2ZnO$
- b) $2ZnS+3O_{2}\rightarrow2ZnO+2SO_{2}$
- c) $MgCO_{3}\rightarrow MgO+CO_{2}$ ✓ Correct
- d) Both (a) and (c)
Answer: c) $MgCO_{3}\rightarrow MgO+CO_{2}$
4. The metal oxide which cannot be reduced to metal by carbon is
- a) PbO
- b) Al2O3 ✓ Correct
- c) ZnO
- d) FeO
Answer: b) Al2O3
5. Which of the metal is extracted by Hall - Heroult process?
- a) Al ✓ Correct
- b) Ni
- c) Cu
- d) Zn
Answer: a) Al
6. Which of the following statements, about the advantage of roasting of sulphide ore before the reduction is not true?
- a) $\triangle G^{\circ}f$ of sulphide is greater than those for CS2 and H2S
- b) $\Delta G^{\circ}r$ is negative for roasting of sulphide ore to oxide
- c) Roasting of the sulphide to its oxide is thermodynamically feasible.
- d) Carbon and hydrogen are suitable reducing agents for metal sulphides. ✓ Correct
Answer: d) Carbon and hydrogen are suitable reducing agents for metal sulphides.
7. Match items in Column I - with the items of Column - II and assign the correct code.
| Column-I | Column-II |
|---|---|
| A. Cyanide process | (i) Ultrapure Ge |
| B. Froth floatation process | (ii) Dressing of ZnS |
| C. Electrolytic reduction | (iii) Extraction of Al |
| D. Zone refining | (iv) Extraction of Au |
| (v) Purification of Ni |
- a) (iii) (iv) (v) (i)
- b) (iv) (ii) (iii) (i)
- c) (iv) (ii) (iii) (i) ✓ Correct
- d) (ii) (iii) (i) (v)
Answer: c) (iv) (ii) (iii) (i)
8. Wolframite ore is separated from tinstone by the process of
- a) Smelting
- b) Calcination
- c) Roasting
- d) Electromagnetic separation ✓ Correct
Answer: d) Electromagnetic separation
9. Which one of the following is not feasible
- a) $Zn(S)+Cu^{2+}(aq)\rightarrow Cu(s)+Zn^{2+}(aq)$
- b) $Cu(S)+Zn^{2+}(aq)\rightarrow Zn(s)+Cu^{2+}(aq)$ ✓ Correct
- c) $Cu(S)+2Ag^{+}(aq)\rightarrow Ag(s)+Cu^{2+}(aq)$
- d) $Fe(S)+Cu^{2+}(aq)\rightarrow Cu(s)+Fe^{2+}(aq)$
Answer: b) $Cu(S)+Zn^{2+}(aq)\rightarrow Zn(s)+Cu^{2+}(aq)$
10. Electrochemical process is used to extract
- a) Iron
- b) Lead
- c) Sodium ✓ Correct
- d) Silver
Answer: c) Sodium
11. Flux is a substance which is used to convert
- a) Mineral into silicate
- b) Infusible impurities to soluble impurities ✓ Correct
- c) Soluble impurities to infusible impurities
- d) All of these
Answer: b) Infusible impurities to soluble impurities
12. Which one of the following ores is best concentrated by froth floatation method?
- a) Magnetite
- b) Heamatite
- c) Galena ✓ Correct
- d) Cassiterite
Answer: c) Galena
13. In the extraction of aluminium from alumina by electrolysis, cryolite is added to
- a) Lower the melting point of alumina ✓ Correct
- b) Remove impurities from alumina
- c) Decrease the electrical conductivity
- d) Increase the rate of reduction
Answer: a) Lower the melting point of alumina
14. Zinc is obtained from ZnO by
- a) Carbon reduction ✓ Correct
- b) Reduction using silver
- c) Electrochemical process
- d) Acid leaching
Answer: a) Carbon reduction
15. Extraction of gold and silver involves leaching with cyanide ion. silver is later recovered by (NEET - 2017)
- a) Distillation
- b) Zone refining
- c) Displacement with zinc ✓ Correct
- d) liquation
Answer: c) Displacement with zinc
16. Considering the Ellingham diagram, which of the following metals can be used to reduce alumina? (NEET - 2018)
- a) Fe
- b) Cu
- c) Mg ✓ Correct
- d) Zn
Answer: c) Mg
17. The following set of reactions are used in refining Zirconium
$Zr(impure)+2I_{2}\xrightarrow{523K}ZrI_{4}$
$ZrI_{4}\xrightarrow{1800K}Zr(pure)+2I_{2}$
This method is known as
- a) Liquation
- b) Van Arkel process ✓ Correct
- c) Zone refining
- d) Mond's process
Answer: b) Van Arkel process
18. Which of the following is used for concentrating ore in metallurgy?
- a) Leaching
- b) Roasting
- c) Froth floatation
- d) Both (a) and (c) ✓ Correct
Answer: d) Both (a) and (c)
19. The incorrect statement among the following is
- a) Nickel is refined by Mond's process
- b) Titanium is refined by Van Arkel's process
- c) Zinc blende is concentrated by froth floatation
- d) In the metallurgy of gold, the metal is leached with a dilute sodium chloride solution ✓ Correct
Answer: d) In the metallurgy of gold, the metal is leached with a dilute sodium chloride solution
20. In the electrolytic refining of copper, which one of the following is used as anode?
- a) Pure copper
- b) Impure copper ✓ Correct
- c) Carbon rod
- d) Platinum electrode
Answer: b) Impure copper
21. Which of the following plot gives Ellingham diagram
- a) $\triangle S$ VST
- b) $\Delta G^{\circ}$ VsT ✓ Correct
- c) $\triangle G^{\circ}Vs1/T$
- d) $\triangle G^{\circ}VsT^{2}$
Answer: b) $\triangle G^{\circ}VsT$
22. In the Ellingham diagram, for the formation of carbon monoxide
- a) $(\frac{\Delta S^{0}}{\Delta T})$ is negative
- b) $(\frac{\Delta G^{0}}{\Delta T})$ is positive
- c) $(\frac{\Delta G^{0}}{\Delta T})$ is negative ✓ Correct
- d) initially $(\frac{\Delta T}{\Delta G^{0}})$ is positive, after $700^{\circ}C$, $(\frac{\Delta G^{0}}{\Delta T})$ is negative
Answer: c) $(\frac{\Delta G^{0}}{\Delta T})$ is negative
23. Which of the following reduction is not thermodynamically feasible?
- a) $Cr_{2}O_{3}+2Al\rightarrow Al_{2}O_{3}+2Cr$
- b) $Al_{2}O_{3}+2Cr\rightarrow Cr_{2}O_{3}+2Al$ ✓ Correct
- c) $3TiO_{2}+4Al\rightarrow2Al_{2}O_{3}+3Ti$
- d) None of these
Answer: b) $Al_{2}O_{3}+2Cr\rightarrow Cr_{2}O_{3}+2Al$
24. Which of the following is not true with respect to the Ellingham diagram?
- a) Free energy changes follow a straight line. The deviation occurs when there is a phase change.
- b) The graph for the formation of CO2 is a straight line almost parallel to the free energy axis. ✓ Correct
- c) Negative slope of CO shows that it becomes more stable with an increase in temperature.
- d) Positive slope of metal oxides shows that their stabilities decrease with an increase in temperature.
Answer: b) The graph for the formation of CO2 is a straight line almost parallel to the free energy axis.
Question 1.
What is the difference between minerals and ores?
Answer:
Minerals:
- Minerals contain a low percentage of metal.
- Metal cannot be extracted easily from minerals.
- Clay Al2O3. SiO2. 2H2O is the mineral of aluminium.
Ores:
- Ores contain a large percentage of metal.
- Ores can be used for the extraction of metals on a large scale readily and economically.
- Bauxite Al2O3. 2H2O is the ore of aluminium.
Question 2.
What are the various steps involved in the extraction of pure metals from their ores?
Answer: Steps involved in the extraction of pure metals from their ores are:
- Concentration of the ore.
- Extraction of the crude metal.
- Refining of the crude metal.
Question 3.
What is the role of Limestone in the extraction of iron from its oxide Fe2O3?
Answer:
- Limestone (CaO) is used as a flux in the extraction of iron from its oxide Fe2O3.
- Flux is a chemical substance that forms an easily fusible slag with gangue.
- Oxide of iron can be reduced by carbon monoxide as follows:
$Fe_{2}O_{3(s)}+3CO_{(g)}\rightarrow2Fe(s)+3CO_{2(g)}$ ↑- In this extraction, a basic flux quick lime (or) lime (CaO) reacts with acidic gangue silica to form the slag calcium silicate.
CaO (s) + SiO, (s) → CaSiO, (s)
Flux + Gangue → Slag
Question 4.
Which type of ores can be concentrated by froth floatation method? Give two examples for such ores.
Answer:
Sulphide ores can be concentrated by the froth floatation method.e.g.,
- Copper pyrites (CuFeS2H2)
- Zinc blende (ZnS)
- Galena (PbS)
Question 5.
Describe a method for refining nickel Mond process for refining nickel: (PTA - 3)
Answer:
- Impure nickel is heated in a stream of carbon monoxide at around 350K. Nickel reacts with CO to form a highly volatile nickel tetracarbonyl. The solid impurities are left behind.
$Ni(s)+4CO(g)\rightarrow Ni(CO)4(g)$- On heating nickel tetra carbonyl around 460K, the complex decomposes to give a pure nickel.
$Ni(CO)4(g)\rightarrow Ni(s)+4CO(g)$
Question 6.
Explain the zone refining process with an example. (PTA- 6 MARCH 2020)
Answer:
- Zone Refining method is based on the principles of fractional crystallisation. When an impure metal is melted and allowed to solidify, the impurities will prefer to be in the molten region, i.e. impurities are more soluble in the melt than in the solid-state metal.
- In this process, the impure metal is taken in the form of a rod. One end of the rod is heated using a mobile induction heater which results in the melting of the metal on that portion of the rod.
- When the heater is slowly moved to the other end the pure metal crystallises while the impurities will move on to the adjacent molten zone formed due to the movement of the heater. As the heater moves further away, the molten zone containing impurities also moves along with it.
- The process is repeated several times by moving the heater in the same direction again and again to achieve the desired purity level.
- This process is carried out in an inert gas atmosphere to prevent the oxidation of metals.
- Elements such as germanium (Ge), silicon (Si) and gallium (Ga) that are used as semiconductors are refined using this process.
Question 7.
Using the Ellingham diagram:
(A) Predict the conditions under which
i) Aluminium might be expected to reduce magnesia.
ii) Magnesium could reduce alumina.
(B) It is possible to reduce Fe2O3 by coke at a temperature around 1200K
Answer:
A)
i) Ellingham diagram for the formation of Al2O3 and MgO intersects around 1600K. Above this temperature aluminium line lies below the magnesium line. Hence we can use aluminium to reduce magnesia above 1600K.
ii) In Ellingham diagram below 1600K magnesium line lies below aluminium line. Hence below 1600K magnesium can reduce alumina.B)
In Ellingham diagram above 1000K carbon line lies below the iron line. Hence it is possible to reduce Fe2O3 by coke at a temperature around 1200K.
Question 8.
Give the uses of zinc. (PTA-4)
Answer:
- Metallic zinc is used in galvanisation to protect iron and steel structures from rusting and corrosion.
- Zinc is used to produce die - castings in the automobile, electrical and hardware industries.
- Zinc oxide is used in the manufacture of paints, rubber, cosmetics, pharmaceuticals, plastics, inks, batteries, textiles and electrical equipment.
- Zinc sulphide is used in making luminous paints, fluorescent lights and x-ray screens.
- Brass an alloy of zinc which is highly resistant to corrosion is used in water valves and communication equipment.
Question 9.
Explain the electrometallurgy of aluminium.
Answer:
Hall - Heroult Process
- Cathode: Iron tanked lined with carbon
- Anode: Carbon blocks
- Electrolyte: 20% solution of alumina obtained from bauxite + Molten Cryolite +10% calcium chloride (lowers the melting point of the mixture)
- Temperature: Above 1270K
Ionisation of Alumina: $Al_{2}O_{3}\rightarrow+2Al_{3+}+3O_{2-}$
Reaction at cathode: $Al3+(melt)+3e-\rightarrow Al|$
Reaction at anode: 202- $(melt)\rightarrow O_{2}(melt)+4e-$Since carbon acts as anode the following reaction also takes place on it.
$C(s)+O_{2}(melt)\rightarrow CO+2e-$
$C(s)+2O_{2}(melt)\rightarrow CO_{2}+4e-$During electrolysis, anodes are slowly consumed due to the above two reactions. Pure aluminium is formed at the cathode and settles at the bottom.
Net electrolysis reaction is:
4Al3+ (melt) + 602- (melt) + 3C(s) → 4AI(1) + 3CO2(g)
Question 10.
Explain the following terms with suitable examples, i) Gangue ii) Slag (PAT - 2)
Answer:
i) Gangue:
The non-metallic impurities, rocky materials and siliceous matter present in the ores are called gangue.
(eg): SiO2 is the gangue present in the iron ore Fe2O3.ii) Slag:
Slag is a fusible chemical substance formed by the reaction of gangue with a flux.
$\supset aO(s)+SiO_{2}(s)\rightarrow CaSiO_{3}(s)$
Flux + Gangue → Slag