2015 SPECIMEN MOCK EXAMINATION CHEMISTRY PAPER 2 MARKING SCHEME

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1 2015 SPECIMEN MOCK EXAMINATION CHEMISTRY PAPER 2 MARKING SCHEME 1. a) i) - Manganese (IV) 1 oxide (penalize if formula) - Hydrogen peroxide 1 (penalize for formula) b) 2H 2 O 2(l) MnO 2 2H 2 O (l) + O 2(g) c) i) - To ensure that all oxygen has been used. 1 ii) - For maximum contact between copper and oxygen so that the reaction occurs 1 iii) - Brown copper turnings charged their colour to a black solid 1 iv) 2Cu (s) + O 2(g) 2CuO (s) v) 120cm cm 3 = 24.5cm x 100 ½ 120 = 20.42% ½ vii) Used by patients with respiratory problems d) 2NaNO 3(s) heat 2NaNO 2(s) + O 2(g) ½ RFM = = 170 => 22.4dm ½ 8.5g? 8.5 x 22.4 = 1.12dm a) i) Ammonia ½ ii) Carbon (IV) oxide ½ iii) Carbon / coke / Graphite / Diamond ½ iv) Calcium oxide ½ v) Ammonium chloride ½ vi) Sodium hydrogen carbonate ½ (penalize for formula) b) i) Chamber I CaO (s) + H 2 O (l) Ca(OH) 2(aq) Chamber II 2NH 4 Cl (aq) + Ca(OH) 2(aq) 2NH 3(g) + CaCl 2(aq) + 2H 2 O (l) (allow rules of balancing equation) c) - Used as a drying agent when in anhydrous form for gases that do not react with it - Used during extraction of sodium metal from sodium chloride to lower the melting point of electrolyte from C to C (award 1mk for any one above) KCPE-KCSE.COM 1

2 d) Ammonia Carbon (IV) oxide e) - Glass making - In pulp and paper industry - Manufacture of sodium silicate - Water softening - Cattle lick (Any two above, award 1mk) f) i) Excess supply of oxygen/ air 1 ii) Limited supply of oxygen / air 1 iii) Bubble each gas separately through calcium hydroxide solution 1 carbon (IV) oxide forms a white precipitate while carbon (II) oxide does not 1 3. a) Molar heat of fusion is the amount of heat energy required to convert one mole of a solid substance at its melting point into a liquid. b)i) The heat of neutralization for reaction (I) is higher than that of II. Reaction I involves hydration energy for K + and OH - ions and neutralization energy while reaction II involves only neutralization energy ii) Reaction a Mg 2+ is a smaller ion than Ca 2+.Hence Mg 2+ ion form stronger forces of attraction with water than Ca 2+ ion during hydration. iii) Ignition provides activation energy for the combustion reaction to begin. c) a) Hess s law states that the energy change in converting reactants to products is the same regardless of the route by which the chemical change occurs. 1 b) Zinc is more reactive than copper, hence displaces it from solution 1 Zn is a stronger reducing agent than copper i) Zn (s) + Cu 2+ (aq) Zn 2+ (aq) + Cu (s) ii) H = -227 ΔH 1 = ΔH 1 = -170kJ mol a) i) Solution A Name sodium hydroxide ½ Formula NaOH ½ ii) Zinc Hydroxide ½ Formula: Zn(OH) 2 ½ b) i) Zn (s) + H 2 SO 4(aq) ZnSO 4(aq) + H 2(g) ii) Zn(OH) 2(g) + 2HCl (aq) ZnCl 2(aq) + 2H 2 O (l) c) Introduce a burning splint to the gas jar full of hydrogen gas ½ It burns with a pop sound ½ KCPE-KCSE.COM 2

3 d) - Sodium metal darts on the surface of the water - A hissing sound is produced 1 e) i) Heat solution E over a water bath to evaporate excess water; when crystals are almost forming remove from fire and leave it to cool slowly 1 ii) Heat the solution directly until all the water has evaporated to remain with a white powder of Zinc chloride 1 f) Zn (s) + 2HCl (aq) ZnCl 2(aq) + H 2(g) 5. a) KCPE-KCSE.COM 3

4 i) 14 minutes ½ (showing of the graph ½ ) ii) Carbonate was used up / consumed 1 iii) 480cm 3 1 b) i) MCO 3(s) + 2HNO 3(aq) M(NO 3 ) 2(aq) + CO 2(g) + H 2 O (l) ii) If 480cm 3 given by 2.5g cm 3 will be given by KCPE-KCSE.COM 4

5 24000 x = 125g ½ iii) MCO 3(s) = 125g M = 125g ½ M = M = 65 ½ 6. a) 4 P alpha / / He ½ 2 Q Gamma / R Beta / o 1 e ½ b) i) Nuclear reactions involve the protons and neutrons while chemical reactions involve electrons 1 ii) Nucleas reactions are not affected by external factors such as temperature while chemical reactions are affected 1 c) i) C and C ii) o C N iii) Carbon dating 1 d) i) Half life Time taken for any amount of a radioactive substance to decay to half the initial mass 1 ii) 25g 1 st 12g5g 2 nd 6g 25g 3 rd 3.125g No of half lifes = 3 1 half - life = 6 / 3 = 2hrs 1 e) - Treatment of cancer - To detect blood circulation disorders - To study the condition of thyroid gland (Any 2 x 1 = 2mks) 7. a) i) A and E 1 ii) C, D, E (any 2 award 1mk each) b) i) D 3+ is smaller than E 2+ 1 D 3+ has a greater nuclear charge ½ thus greater attraction ½ electrons. ii) E is more reactive than A 1 E has a larger atomic radius ½ hence outermost electrons are more loosely held ½ hence easily lost than those of A. c) i) C ½ ii) D d) i) EB 2 1 Reject B 2 E ii) Ionic /electrovalent ½ - It involves transfer of electrons from A to oxygen ½ KCPE-KCSE.COM 5