General Principles of Isolation of Elements

The Gibbs energy for the decomposition of Al2O3 at 500 is as follows 23Al2O3 43Al + O2 rG = +960 kJ mol-1 The potential difference needed for the electrolytic reduction of aluminium oxide (Al2O3) at 500 is at least

1. 4.5 V
2. 3.0 V
3. 2.5 V
4. 5.0 V

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

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

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

Which one of the following is a mineral of iron?

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

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.

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)

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

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

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

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

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

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

1. The fG of the sulphide is greater than those for CS2 and H2S.
2. The fG 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.

The mass of carbon anode consumed (giving only carbon dioxide) in the production of 270 kg of aluminium metal from bauxite by the Hall process is (Atomic mass : Al = 27)

1. 270 kg
2. 540 kg
3. 90 kg
4. 180 kg