CBSE Class 12 Chemistry General Principles And Processes Of Isolation Of Elements Worksheet

One mark Questions

1.Differentiate between a mineral and an ore.

Ans: the naturally occurring chemical substances present in the earth’s crust which can be obtained by mining are called minerals while minerals from which metals can be extracted economically are called ores.

2. Why is it that only sulphide ores are concentrated by froth floatation process.

Ans: This is because sulphide ores particles are wetted by oil and gangue particles are wetted by water.

3. Name one acidic flux and one basic flux.

Ans: silica and lime

4. Name the chief ore of silver.

Ans: argentite or silver glance

5. Name a reagent used during leaching of bauxite ore.

Ans : NaOH (sodium hydroxide)

6. Why is silica added to sulphide ore of copper in the reverberatory furnace?

Ans : in order to remove the iron impurity as slag

7. What is the role of flux in metallurgical processes?

Ans : flux is used for making the molten mass more conducting.

8. What is the thermodynamic relation between Gibbs free energy and emf of the cell.

Ans: ΔG⁰= —nFE⁰

9. What is the relation between gibbs free energy and equilibrium constant?

Ans: ΔG⁰= —RTlnK

10. Give the expression for Gibbs Helmholtz equation. 

Ans : ΔG= ΔH—TΔS

11. Name one chemical which can be used to concentrate galena selectively by froth floatation process.

Ans: sodium cyanide (NaCN)

12. What type of ores are roasted?

Ans : sulphide ores

13. Out of C and CO which is a better reducing agent for ZnO?

Ans : the free energy of formation of CO from C becomes lower at temp. above 1120K whereas that of CO₂ from C becomes lower above 1323K than free energy of formation of ZnO. The free energy of formation of from CO is always higher than that of ZnO. Therefore, C can reduce ZnO to Zn better than CO. CO₂ from CO is always higher than that of ZnO. Therefore, C can reduce ZnO to Zn better than CO.

14. What is the chemical principle on which chromatography separation based on?

Ans : Adsorption

15. What are the products obtained during the electrolysis of brine solution? Also write the name of this process.

Ans : chlorine, hydrogen and sodium hydroxide. The process is popularly known as chlor-alkali process.

Important Questions for NCERT Class 12 Chemistry General Principles Process of Isolation of Elements

Question. Nitriding is the process of surface hardening of steel by treating it in an atmosphere of
(a) NH₃
(b) O₃
(c) N₂
(d) H₂S

Question. Aluminium is extracted from alumina (Al₂O₃) by electrolysis of a molten mixture of
(a) Al₂O₃ + HF + NaAlF₄
(b) Al₂O₃ + CaF₂ + NaAlF₄
(c) Al₂O₃ + Na₃AlF₆ + CaF₂
(d) Al₂O₃ + KF + Na₃AlF₆ 

Question. Purification of aluminium, by electrolytic refining, is known as
(a) Hoope’s process
(b) Baeyer’s process
(c) Hall’s process
(d) Serpeck’s process. 

Question. Calcium is obtained by
(a) reduction of calcium chloride with carbon
(b) electrolysis of molten anhydrous calcium chloride
(c) roasting of limestone
(d) electrolysis of solution of calcium chloride in H₂O.

Question. Extraction of gold and silver involves leaching with
CN– ion. Silver is later recovered by
(a) distillation
(b) zone refining
(c) displacement with Zn
(d) liquation

Question. Identify the correct statement from the following :
(a) Wrought iron is impure iron with 4% carbon.
(b) Blister copper has blistered appearance due to evolution of CO₂.
(c) Vapour phase refining is carried out for Nickel by van Arkel method.
(d) Pig iron can be moulded into a variety of shapes.

Question. Which of the following pairs of metals is purified by van Arkel method?
(a) Ga and In
(b) Zr and Ti
(c) Ag and Au
(d) Ni and Fe 

Question. The method of zone refining of metals is based on the principle of
(a) greater mobility of the pure metal than that of the impurity
(b) higher melting point of the impurity than that of the pure metal
(c) greater noble character of the solid metal than that of the impurity
(d) greater solubility of the impurity in the molten state than in the solid.

Question. 2CuFeS₂ +O₂ →Cu₂S + 2FeS + SO₂ Which process of metallurgy of copper is represented by above equation? 
(a) Concentration
(b) Roasting
(c) Reduction
(d) Purification

ONE MARK QUESTIONS

1.Out of C and CO, which is a better reducing agent at 673 K?

TWO MARK QUESTIONS

1.Describe the role of

a) Iodine in the refining of titanium.

b) Collector in the froth floatation process.

2.Describe how the following changes are brought out:

a) Pig iron into steel

b) Zinc oxide into zinc metal.

THREE MARK QUESTIONS

1.Differentiate between

a) Calcination and roasting

b) Electrolytic reduction and electrolytic refining

c) Flux and slag

2.Write the chemical reactions which take place in the following operations:

a) Electrolytic reduction of Al₂O₃.

b) Isolation of Zn from zinc blende.

c) Mond’s process for refining of Ni.

3.Give reasons:

a) Copper matte is put in silica lined convertor.

b) Cryolite is added to alumina during electrolytic reduction.

c) Pine oil is used in the froth floatation process

4.a) Name the method used for the refining of titanium. b) What is the role of Zn in the extraction of silver? c) Reduction of metal oxide to metal becomes easier if the metalobtained is in liquid state. Why?

VALUE BASED QUESTION

1.Sam owns sites from where copper with other metals are mined. At sites he found the low grade copper ores are available with zinc and iron scraps.

a) Which of the two scraps should Sam use for the reduction of leached copper and why?

b) Mention the value in Sam’s choice.

c) What do you mean by blister copper?

d) Why is extraction of copper from copper pyrite more difficult than that from its oxide ore through reduction?

Important Questions for NCERT Class 12 Chemistry General Principles Process of Isolation of Elements

Question. The metal oxide which cannot be reduced to metal by carbon is
(a) Al2O₃
(b) PbO
(c) ZnO
(d) Fe2O₃

Question. Carbon and CO gas are used to reduce which of the following pairs of metal oxides for extraction of metals? 
(a) FeO, SnO
(b) SnO, ZnO
(c) BaO, Na2O₂
(d) FeO, ZnO

Question. Which of the following elements is present as the impurity to the maximum extent in the pig iron?
(a) Manganese
(b) Carbon
(c) Silicon
(d) Phosphorus

Question. In metallurgical process of aluminium, cryolite is mixed with alumina in its molten state, because it 
(a) decreases the amount of alumina
(b) oxidises the alumina
(c) increases the melting point of alumina
(d) decreases the melting point of alumina

Question. The following reactions take place in the blast furnace in the preparation of impure iron. Identify the reaction pertaining to the formation of the slag.
(a) Fe₂O₃(s) + 3CO(g) → 2Fe(l) + 3CO₂(g)
(b) CaCO₃(s) → CaO(s) + CO₂(g)
(c) CaO(s) + SiO₂(s) → CaSiO₃(s)
(d) 2C(s) + O₂(g) → 2CO(g)

Question. Sulfide ores are common for the metals 
(a) Ag, Cu and Pb
(c) Ag, Cu and Sn
(b) Ag, Mg and Pb
(d) Al, Cu and Pb

Question. Which of the following statements, about the advantage of roasting of sulphide ore before reduction is not true?
(a) The DGf° of the sulphide is greater than those for CS2 and H2S.
(b) The DGf° is negative for roasting of sulphide ore to oxide.
(c) Roasting of the sulphide to the oxide is thermodynamically feasible.
(d) Carbon and hydrogen are suitable reducing agents for metal sulphides.

Question. The main reactions occurring in blast furnace during extraction of iron from haematite are________.
(i) Fe₂O₃ + 3CO → 2Fe + 3CO₂
(ii) FeO + SiO₂ → FeSiO₃
(iii) Fe2O3 + 3C → 2Fe + 3CO
(iv) CaO + SiO₂ → CaSiO₃
(a) (i) and (iii)
(b) (ii) and (iv)
(c) (i) and (iv)
(d) (i), (ii) and (iii)