Pure Chemistry Compiled Nov 2020 P2 to Nov 2012 P2 ANS

1 GCE ‘O’ Level Examinations 2020 Chemistry 6092 Paper 2 Section A [50 marks] 1 (a) (i) calcium hydroxide 1 (ii) hydrogen and iron 1 (iii) argon / graphite 1 (iv) ethanol 1 (v) graphite 1 (vi) graphite and hydrogen 1 (b) true true false false 2 2 (a) The temperature in the car engine is very high and nitrogen and oxygen molecules gain kinetic energy and move faster. The frequency of collisions increases . More n itrogen and oxygen molecules collide with energy greater than activation energy and the frequency of effective collisions increases. For a reaction to take place, the reactant particles must collide with energy that is equal to or greater than the activation energy. At room temperature, the molecules do not have sufficient energy that is equal to or greater than the activation energy, hence, there is no reaction at room temperature. 1 1 1 (b) (i) Equation 1: 2NO(g) + O2 (g) → 2NO2(g) Equation 2: 4NO2(g) + 2H2O (l) + O2 → 4HNO3 (aq) 1 1 (ii) Sulfur dioxide 1 3 (a) (b) In metals, the sea of electrons are delocalised and are free to move about / mobile around the positive ions. In ionic compounds, they are able to conduct electricity only in molten or aqueous states. Both positively charged cations and negatively charged anions are free to move about in molten and aqueous state and act as charged carriers. 1 1

2 (c) (i) Mild steel is an alloy of iron with carbon atoms. Iron and carbon atoms are of different sizes. The regular arrangement of atoms in the pure iron is disrupted with the inclusion of carbon atoms. The layers of atoms cannot slide over each other easily when the force is applied. As a result, mild steel is stronger than pure iron. 1 1 (ii) With reference to the diagram, the size of an iron atom is smaller than the size of a carbon atom. However, this is not accurate as the atomic radius of an iron atom (0.126 nm) is larger than the atomic radius of a carbon atom (0.077 nm). Mild steel is an alloy consisting of iron (99%), carbon (0.25%) and manganese (0.4%) atoms. However, manganese atoms are absent in the diagram. With reference to the diagram, the proportion / percentage of iron atoms (24 atoms) to carbon atoms (4 atoms) is much lesser/lower, which is not an accurate representation of the ratio 99 : 0.25. 2 4 (a) An electrolytic cell is being set up. The anode will be the tin metal and is connected to the positive terminal of the battery. The cathode will be the iron can and is connected to the negative terminal of the battery. Both anode and cathode are pla ced in an electrolyte which is the aqueous tin(II) nitrate solution. 1 1 1 (b) Sn(s) + 2 H+ (aq) → Sn2+ (aq) + H2 (g) 1 mark – correct ionic equation. 1 mark – correct state symbol 2 (c) (i) Poly(ethene) will not corrode and produce toxic substances so that it is safer for consumers to use.