INTI COLLEGE MALAYSIA A? LEVEL PROGRAMME CHM 111: CHEMISTRY MOCK EXAMINATION: DECEMBER 2000 SESSION m/e

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1 CHM111(M)/Page 1 of 5 INTI COLLEGE MALAYSIA A? LEVEL PROGRAMME CHM 111: CHEMISTRY MOCK EXAMINATION: DECEMBER 2000 SESSION SECTION A Answer ALL EIGHT questions. (52 marks) 1. The following is the mass spectrum of chlorine, Cl 2. Intensity m/e Identify the species responsible for each peak in the spectrum. Why are the first two peaks of different heights? 2. Describe the bonding in copper and explain how it conducts electricity. Describe the bonding in magnesium oxide and explain why it acts as an insulator.

2 CHM111(M)/Page 2 of 5 3. The atomic numbers of copper and iron are 29 and 26 respectively. What are the electronic configurations of Cu, Fe 2+ and Fe 3+? Comment on the relative stabilities of the iron (II) and iron (III) ions. 4. Describe the relative masses and relative charges of the three sub-atomic particles : protons, neutrons and electrons. (4 marks) Describe, by means of a diagram, how the paths of separate beams of (iii) protons, deuterons, hydrogen atoms, are affected on passing through an electric field. 5. When 4.20 g of a compound was completely vaporised in a gas syringe at 27 o C and a pressure of 8 x 10 4 Pa, 1.00 dm 3 of vapour was produced. Calculate the relative molecular mass of the compound. (7 marks) 6. Calculate the lattice energy of CaO given that: (c) (d) (e) (f) the enthalpy change of atomisation of Ca is 177 kj mol?1, and the enthalpy change of atomisation of O 2 is 250 kj mol?1, and the first ionisation energy of Ca is 587 kj mol?1, and the second ionisation energy of Ca is 1156 kj mol?1, and the enthalpy change of formation of CaO is 637 kj mol?1, and the energy required to form one mole of O 2? ion from gaseous oxygen atom is 704 kj. (7 marks)

3 CHM111(M)/Page 3 of 5 7. State Le Chatelier s principle. In relation to the following equilibria, Equilibrium I: H 2 O(g) + C(s)? H 2 (g) + CO(g);? H = +131 kj mol?1 Equilibrium II: 2Cr 2 O 4? (aq) + 2H + (aq)? Cr 2 O 7 2? (aq) + H 2 O(l) use Le Chatelier s principle to explain the effect of increasing the pressure on Equilibrium I, increasing the temperature on Equilibrium I, (iii) increasing [H + (aq)] on Equilibrium II. 8. What do you understand by the terms strong and weak when applied to acids? The acid dissociation constant, K a, for methanoic acid is 1.8 x 10?4 mol dm?3. In a 0.01 mol dm?3 solution of methanoic acid, calculate (iii) the concentration of hydrogen ions; the ph; the concentration of hydroxide ions. [K w = 1.0 x 10?14 mol 2 dm?6 ]

4 CHM111(M)/Page 4 of 5 SECTION B Answer any THREE questions. (48 marks) 9. State Hess s Law (4 marks) The following is a table of some standard molar enthalpy changes of formation. Substance? H f (298K) / kj mol?1 ClF(g)?63.4 Cl(g) [½Cl 2 (g)? Cl (g)] F(g) [½F 2 (g)? F(g) ] 79.0 Use these values to calculate the molar bond dissociation energy of Cl F. (12 marks) 10. What do you understand by the Bronsted-Lowry theory of acids and bases? For each of the following reactions A and B: identify the two acids and the two bases present; suggest, with reasons, which ion or molecule is the stronger acid, and which of them is the stronger base. A NH 3 + H 2 O? NH OH? ; K c = 1.8 x 10?5 mol dm?3 B C 6 H 5 O? + CH 3 CO 2 H? C 6 H 5 OH + CH 3 CO? 2 ; K c = 1.3 x 10 6 mol dm?3 (8 marks) (c) The ph of a 0.1 mol dm?3 solution of CH 3 CO 2 H is 2.4, whereas the ph of a 0.1 mol dm?3 solution of HCl is 1.0. Calculate the ratio of hydrogen ion concentrations in these two solutions. (6 marks) 11. An organic acid has the following composition by mass: C, 40.0%; H, 6.7%; O, 53.3%. Its mass spectrum shows major peaks (including the molecular ion) at the following m/e (mass) values: 15, 43, 45, 60.

5 CHM111(M)/Page 5 of 5 Calculate the empirical formula of the acid, and use the mass spectrum to suggest its molecular formula. (10 marks) Identify the various species responsible for peaks in the mass spectrum and suggest their molecular formulae. (6 marks) 12. When 100 cm 3 of a hydrocarbon is burned in 500 cm 3 of oxygen, 50 cm 3 of oxygen are unused, 300 cm 3 of carbon dioxide are formed and 300 cm 3 of steam are formed. Deduce the equation for the reaction and the formula of the hydrocarbon. (16 marks) 13. Part of the process by which coal can be converted into a combustible mixture of gases involves passing steam over hot coke: H 2 O(g) + C(s)? H 2 (g) + CO(g);? H = +131 kj mol?1 (c) For this reaction, write an expression for K p, the equilibrium constant, in terms of partial pressures. State and explain how the composition of the equilibrium mixture would change if there were an increase in the pressure, the temperature. (8 marks) When steam was passed over coke at 730 o C, the following partial pressures were measured at equilibrium:?(h 2 O) = 90 kpa,?(h 2 ) = 183 kpa. State what the equilibrium partial pressure of carbon monoxide is and hence calculate the equilibrium constant. -THE END- CHM 111/DEC00tr.doc26012k1 Winword/small disk/yuvani