NEET Chemistry: General Principles of Isolation of Elements questions with solutions

Q1. Which one is malachite from the following?

1. CuFeS2
2. Cu(OH)2
3. Fe3O4
4. CuCO3·Cu(OH)2

Answer: CuCO3·Cu(OH)2

Malachite is a basic copper carbonate with the chemical formula CuCO3·Cu(OH)2, which is a well-known green mineral.

Q2. Which one of the following is a mineral of iron?

1. Malachite
2. Cassiterite
3. Pyrolusite
4. Magnetite

Answer: Magnetite

Magnetite is a mineral of iron, while malachite is a copper mineral, cassiterite is a tin mineral, and pyrolusite is a manganese mineral.

Q3. Extraction of gold and silver involves leaching with CN⁻ ion. Silver is later recovered by

1. distillation
2. zone refining
3. displacement with Zn
4. liquation

Answer: displacement with Zn

Silver is recovered from its cyanide complex by displacement with zinc, as zinc is more reactive and displaces silver from the complex.

Q4. Match items of Column I with the items of Column II and assign the correct code: Column-I: (A) Cyanide process (B) Froth flotation process (C) Electrolytic reduction (D) Zone refining Column-II: (i) Ultrapure Ge (ii) Dressing of ZnS (iii) Extraction of Al (iv) Extraction of Au (v) Purification of Ni

1. (A) (B) (C) (D) - (iv) (ii) (iii) (i)
2. (A) (B) (C) (D) - (ii) (iii) (i) (v)
3. (A) (B) (C) (D) - (ii) (i) (iii) (iv)
4. (A) (B) (C) (D) - (iii) (ii) (iv) (v)

Answer: (A) (B) (C) (D) - (iv) (ii) (iii) (i)

The cyanide process is used for the extraction of gold (Au), froth flotation is used for dressing of zinc sulfide (ZnS), electrolytic reduction is used for the extraction of aluminum (Al), and zone refining is used for obtaining ultrapure germanium (Ge).

Q5. In the extraction of copper from its sulphide ore, the metal finally obtained by the reduction of cuprous oxide with:

1. iron (II) sulphide
2. carbon monoxide
3. copper (I) sulphide
4. sulphur dioxide

Answer: copper (I) sulphide

In the extraction of copper from its sulphide ore, cuprous oxide (Cu2O) is reduced by copper (I) sulphide (Cu2S) in a self-reduction process, forming metallic copper and sulphur dioxide.

Q6. 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: Fe₂O₃(s) + 3CO(g) → 2Fe(l) + 3CO₂(g) CaCO₃(s) → CaO(s) + CO₂(g) CaO(s) + SiO₂(s) → CaSiO₃(s) 2C(s) + O₂(g) → 2CO(g)

1. Fe₂O₃(s) + 3CO(g) → 2Fe(l) + 3CO₂(g)
2. CaCO₃(s) → CaO(s) + CO₂(g)
3. CaO(s) + SiO₂(s) → CaSiO₃(s)
4. 2C(s) + O₂(g) → 2CO(g)

Answer: CaO(s) + SiO₂(s) → CaSiO₃(s)

The reaction CaO(s) + SiO₂(s) → CaSiO₃(s) represents the formation of slag, where calcium silicate (CaSiO₃) is formed as a byproduct in the blast furnace.

Q7. Sulphide ores of metals are usually concentrated by froth flotation process. Which one of the following sulphide ores offer an exception and concentrated by chemical leaching?

1. Galena
2. Copper pyrite
3. Sphalerite
4. Argentite

Answer: Argentite

Argentite (Ag2S) is concentrated by chemical leaching using a cyanide solution, unlike most sulphide ores that are concentrated by froth flotation.

Q8. Which of the following elements is present as the impurity to the maximum extent in the pig iron?

1. Manganese
2. Carbon
3. Silicon
4. Phosphorus

Answer: Carbon

Carbon is the primary impurity in pig iron, typically present in the highest proportion (around 3-4%) compared to other impurities like manganese, silicon, and phosphorus.

Q9. The metal oxide which cannot be reduced to metal by carbon is

1. Fe₂O₃
2. Al₂O₃
3. PbO
4. ZnO

Answer: Al₂O₃

Al₂O₃ cannot be reduced by carbon because aluminum has a very high affinity for oxygen, making its oxide highly stable. Carbon is not a strong enough reducing agent to reduce Al₂O₃ to aluminum.

Q10. The method of zone refining of metals is based on the principle of

1. Greater solubility of the impurity in the molten state than in the solid
2. Greater mobility of the pure metal than that of the impurity
3. Higher melting point of the impurity than that of the pure metal
4. Greater noble character of the solid metal than that of the impurity

Answer: Greater solubility of the impurity in the molten state than in the solid

Zone refining works on the principle that impurities are more soluble in the molten state of a metal than in its solid state, allowing purification as the molten zone moves.

Q11. Method used for obtaining highly pure silicon used as a semiconductor material is

1. Oxidation
2. Electrochemical
3. Crystallization
4. Zone refining

Answer: Zone refining

Zone refining is a method used to obtain highly pure silicon by moving a molten zone along a silicon rod, which removes impurities as it progresses.

Q12. Which of the following pairs of metals is purified by van Arkel method?

1. Ga and In
2. Zr and Ti
3. Ag and Au
4. Ni and Fe

Answer: Zr and Ti

The van Arkel method is used for the purification of metals like zirconium (Zr) and titanium (Ti) by converting them into volatile iodides and then decomposing them to obtain pure metal.

Q13. Which of the following statements, about the advantage of roasting of sulphide ore before reduction is not true?

1. The ΔG⁰ of the sulphide is greater than those for CS₂ and H₂S.
2. The ΔG⁰ is negative for roasting of sulphide ore to oxide.
3. Roasting of the sulphide to the oxide is thermodynamically feasible.
4. Carbon and hydrogen are suitable reducing agents for metal sulphides.

Answer: Carbon and hydrogen are suitable reducing agents for metal sulphides.

Carbon and hydrogen are not suitable reducing agents for metal sulphides because their Gibbs free energy change (ΔG⁰) for the reduction of sulphides is not favorable. This makes option D incorrect.

Q14. Match the following:

1. Sulphuric acid - Contact process
2. Steel - Bessemer’s process
3. Sodium hydroxide - Leblanc process
4. Ammonia - Haber’s process

Answer: Ammonia - Haber’s process

The processes listed are correctly matched with their respective products: Sulphuric acid is made by the Contact process, steel by the Bessemer process, sodium hydroxide by the Leblanc process, and ammonia by the Haber process.

Q15. On heating chromite (FeCr2O4) with Na2CO3 in air, which of the following product is obtained?

1. Na2Cr2O7
2. FeO
3. Fe2O4
4. Na2CrO4

Answer: Na2CrO4

When chromite (FeCr2O4) is heated with Na2CO3 in the presence of air, it undergoes oxidation to form sodium chromate (Na2CrO4). This is a standard reaction in the extraction of chromium.

Q16. Metals are usually not found as nitrates in their ores. Out of the following two (i) and (ii) reasons which is/are true for the above observation? (i) Metal nitrates are highly unstable. (ii) Metal nitrates are highly soluble in water.

1. (a) (i) and (ii) are false
2. (b) (i) is false but (ii) is true
3. (c) (i) is true but (ii) is false
4. (d) (i) and (ii) are true

Answer: (b) (i) is false but (ii) is true

Metal nitrates are highly soluble in water, which prevents their accumulation in ores. However, they are not necessarily unstable, making (ii) true and (i) false.

Q17. In which of the following processes, fused sodium hydroxide is electrolysed at a 330°C temperature for extraction of sodium?

1. Castner's process
2. Down's process
3. Cyanide process
4. Both 'b' and 'c'

Answer: Down's process

In Down's process, fused sodium hydroxide is electrolyzed at high temperatures (around 330°C) to extract sodium metal. The other processes do not involve this specific method.

Q18. Calcium is obtained by the

1. electrolysis of solution of calcium chloride in water
2. electrolysis of molten anhydrous calcium chloride or fused calcium chloride
3. roasting of limestone
4. reduction of calcium chloride with carbon

Answer: electrolysis of molten anhydrous calcium chloride or fused calcium chloride

Calcium is obtained industrially by the electrolysis of molten anhydrous calcium chloride because it is a highly reactive metal and cannot be extracted by reduction or roasting methods.

Q19. Aluminium is extracted from alumina (Al2O3) by electrolysis of a molten mixture of:

1. Al2O3 + HF + NaAlF4
2. Al2O3 + CaF2 + NaAlF4
3. Al2O3 + Na3AlF6 + CaF2
4. Al2O3 + KF + Na3AlF6

Answer: Al2O3 + Na3AlF6 + CaF2

Aluminium is extracted by the Hall-Héroult process, where alumina is dissolved in a molten mixture of cryolite (Na3AlF6) and calcium fluoride (CaF2) to lower the melting point and improve conductivity.

Q20. Which of the following elements is extracted commercially by the electrolysis of an aqueous solution of its compound?

1. Cl
2. Br
3. Al
4. Na

Answer: Cl

Chlorine (Cl) is commercially extracted by the electrolysis of an aqueous solution of sodium chloride (brine), producing chlorine gas at the anode.