(a) Outline the procedures for the treatment of water for town supply.
(b) (i) State two main impurities present in bauxite.
(ii) Give one reason why bauxite is usually preferred as the ore for the extraction of aluminium.
(iii) Outline the manufacture of aluminium form purified bauxite.
(c) (i) Explain briefly the term fine chemical industry.
(ii) State two differences between a fine chemical and a heavy chemical.
(d) (i) Write a balanced chemical equation for the combustion of coal.
(ii) If 5.4 g of coal is burnt completely, calculate the amount of oxygen measured at s.t.p. that would be required for the combustion.
[C = 12.0, O = 16.0, Molar volume of a gas at s.t.p. = \(22.4\ \text{dm}^3\)]
(e) Name two substances which can be used as electrodes during the electrolysis of acidified water.
(a) Treatment of water for town supply
- Screening/sedimentation: the water is screened and allowed to stand so that suspended particles settle, often aided by a coagulant such as alum.
- Filtration: the water passes through beds of sand and gravel to remove fine suspended matter.
- Aeration to improve taste and oxidise dissolved impurities.
- Chlorination (sterilization): chlorine is added to kill germs.
- Storage and distribution to consumers.
(b)(i) Iron(III) oxide (Fe2O3) and silica (SiO2).
(b)(ii) Bauxite is preferred because it is rich in aluminium oxide and is the most abundant and economical source of the metal.
(b)(iii) The purified alumina (Al2O3) is dissolved in molten cryolite (to lower the melting point) and the mixture is electrolysed using carbon (graphite) anodes and a carbon-lined cathode. Aluminium is deposited at the cathode and oxygen is liberated at the anode:
Cathode: \( \text{Al}^{3+} + 3e^- \to \text{Al} \); \quad Anode: \( 2\text{O}^{2-} \to \text{O}_2 + 4e^- \).
(c)(i) A fine chemical industry manufactures chemicals in small quantities but of high purity and high value (e.g. drugs, dyes, cosmetics).
(c)(ii) (1) Fine chemicals are made in small quantities, heavy chemicals in large/bulk quantities. (2) Fine chemicals are of high purity and high cost per unit, whereas heavy chemicals are of lower purity and cheaper per unit.
(d)(i) \[ \text{C} + \text{O}_2 \to \text{CO}_2 \]
(d)(ii) \( n(\text{C}) = \dfrac{5.4}{12} = 0.45\ \text{mol} \); \( n(\text{O}_2) = 0.45\ \text{mol} \).
\[ V = 0.45 \times 22.4 = 10.08\ \text{dm}^3 \]
(e) Platinum and carbon (graphite) (inert electrodes).
(a) Treatment of water for town supply
- Screening/sedimentation: the water is screened and allowed to stand so that suspended particles settle, often aided by a coagulant such as alum.
- Filtration: the water passes through beds of sand and gravel to remove fine suspended matter.
- Aeration to improve taste and oxidise dissolved impurities.
- Chlorination (sterilization): chlorine is added to kill germs.
- Storage and distribution to consumers.
(b)(i) Iron(III) oxide (Fe2O3) and silica (SiO2).
(b)(ii) Bauxite is preferred because it is rich in aluminium oxide and is the most abundant and economical source of the metal.
(b)(iii) The purified alumina (Al2O3) is dissolved in molten cryolite (to lower the melting point) and the mixture is electrolysed using carbon (graphite) anodes and a carbon-lined cathode. Aluminium is deposited at the cathode and oxygen is liberated at the anode:
Cathode: \( \text{Al}^{3+} + 3e^- \to \text{Al} \); \quad Anode: \( 2\text{O}^{2-} \to \text{O}_2 + 4e^- \).
(c)(i) A fine chemical industry manufactures chemicals in small quantities but of high purity and high value (e.g. drugs, dyes, cosmetics).
(c)(ii) (1) Fine chemicals are made in small quantities, heavy chemicals in large/bulk quantities. (2) Fine chemicals are of high purity and high cost per unit, whereas heavy chemicals are of lower purity and cheaper per unit.
(d)(i) \[ \text{C} + \text{O}_2 \to \text{CO}_2 \]
(d)(ii) \( n(\text{C}) = \dfrac{5.4}{12} = 0.45\ \text{mol} \); \( n(\text{O}_2) = 0.45\ \text{mol} \).
\[ V = 0.45 \times 22.4 = 10.08\ \text{dm}^3 \]
(e) Platinum and carbon (graphite) (inert electrodes).
