2021 SAJC Prelim P1 Answer

ST ANDREW’S JUNIOR COLLEGE JC2 Preliminary Examinations Higher 2 CANDIDATE NAME CLASS 2 0 S CHEMISTRY Paper 1 Multiple Choice 9729/01 16 September 2021 1 hour Additional Materials: Multiple Choice Answer Sheet Data Booklet READ THESE INSTRUCTIONS FIRST Write in soft pencil. Do not use staples, paper clips, glue or correction fluid. Write your name and class on the Answer Sheet in the spaces provided. There are thirty questions on this paper. Answer all questions. For each question there are four possible answers A, B, C and D. Choose the one you consider correct and record your choice in soft pencil on the separate Answer sheet. Each correct answer will score one mark. A mark will not be deducted for a wrong answer. Any rough working should be done in this booklet. The use of an approved scientific calculator is expected, where appropriate. This document consists of 15 printed pages.

1 Which of the following contains the same number of particles as 16 g of oxygen atoms? A The number of molecules in 24 dm3 of Cl2 under room conditions B The number of ions in 1 dm3 of 1 mol dm-3 aqueous HCl C The number of atoms in 111.6 g of Fe D The number of formula units of 29.25 g of NaCl Ans: A L = 6.02 X 10-23 mol-1 No. of atoms = 16/32 X 2 X L = 1L molecules A - No. of molecules = 24/24 X 1 X L = L molecules B – No. of ions = 1 X 1 X 2 = 2L ions C – No. of atoms = 111.6/ 55.8 X L = 2L atoms D – No. of formula unit = 29.25/58.5 X L = 0.5 L formula unit 2 The first eight ionisation energies of an element Q (in kJ mol–1) are as follows: 966, 1950, 2730, 4850, 6020, 12300, 15400, 18900 Which of the following statements about element Q is correct? A It can form a basic oxide. B It can form a chloride with the formula QCl5. C It has an even number of protons in its atom. D It can form a chloride that is trigonal planar in shape. Ans: B The increase between the fifth and sixth IE is the largest. Hence, there is 5 valence electrons. Hence, the formula is QCl5. 3 A 2.0 g sample containing 0.0130 mol of organoboron compound, with the formula CxHyBOz, was burnt in an excess of oxygen. 4.58 g of CO 2 and 1.76 g of H 2O were produced. What is the molecular formula of the organoboron compound? A CH2BO2 B C8H7BO2 C C8H15BO2 D C9H15BO Ans: C No. of moles of carbon in sample = 4.58/44 = 0.104 No. of moles of H in sample = 1.76/18 x 2 = 0.196 Value of x = 0.104/0.0130= 8 Value of y = 0.196/0.0130= 15 Mr of sample = 2/0.0130=154 Value of z = (154-96-15-10.8)/16=2

Molecular formula is C8H15BO2. 4 Beams of charged particles travelling at the same speed from different sources are subjected to an electric field in two different experiments. In the first experiment, protons are deflected by an angle of +12o. In another experiment under identical conditions, particle X is deflected by an angle of 4o. What could be the composition of particle X? protons neutrons electrons A 1 2 1 B 3 3 5 C 4 5 1 D 4 5 5 Ans: B For proton, charge/mass ratio = +1/1  +12o Since particle X has angle of deflection 4o , its charge/mass ratio should be 2/6 = 1/3 5 Which molecule has the largest overall dipole moment? A B C D Ans: C Option A and B have overall net dipole of zero or close to zero Option D has a net dipole moment but smaller than that of option C.

6 Which statements about the lattice structure of the crystalline solid of diamond and ice are correct? 1 The hybridisation of the oxygen atom in ice and the carbon atom in diamond are the same. 2 The H-O-H bond angle is 105o while the C-C-C bond angle is 109.5o. 3 The lattice structure are held by strong covalent bonds only. A 1, 2 and 3 B 2 and 3 only C 1 only D 2 only Ans: C Option 1. The hybridisation of the oxygen atom in ice and the carbon atom in diamond are sp3 Option 2. Both are tetrahedral and hence 109.5o. Option 3. Ice is held by hydrogen bonding and covalent bond. 7 The value of pV RT is plotted against p for one mole of each of the two gases, P and Q, where p is the pressure, V is the volume and T is the temperature of the gas. Which of the following pairs of gases could be P and Q? P Q A N2 O2 P Q pV RT 1.0 p

B CH4 CH3Cl C HCl HF D HBr F2 Ans: D HBr is polar, with stronger pd-pd and id-id while F2 is non-polar with id-id only, hence HBr deviates more from ideal gas behaviour. . 8 The following reaction is thermodynamically feasible only at high temperature. C(s) + CO2(g) → 2CO(g) Which row correctly describes the signs of H and S for the reaction? H S A – – B – + C + – D + + Ans: D G = H -TS S must be positive since there are more moles of gases produced. Since the reaction is thermodynamically feasible only at high temperature, H must be positive. 9 Some Hc values are given below. Element Hc / kJ mol–1 H2 –285 C –394 What is the ratio of heat generated by hydrogen to that of carbon if the same mass of each substance is burned? A 0.7 B 1.4 C 3.4 D 4.3 Ans: D Let x be the mass burned. Heat generated from x g of H2 = 285x/2 = 142.5

Heat generated from x g of C = 394x/12 = 32.8 Ratio = 142.5/32.8 = 4.3 10 Some information about some of the elements of Period 5 of the Periodic Table is shown. element Rb Sr In Sn Sb Te I Xe Electrical conductivity high high high high high Semi- conductor zero zero Boiling point/ K 961 1650 2300 2540 1650 1260 457 165 Which statement about these elements is correct? A Te exists as a giant metallic structure with electrostatic forces of attraction. B TeI2 exists as an ionic compound with strong electrostatic forces of attraction. C There are more elements with metallic structures in Period 5 than in Period 3. D Those elements in Period 5 which have a boiling point under 1000 K exist as simple molecules. B M Ans: C A: Te has a giant covalent structure with strong covalent bonds B: TeI2 exists as a covalent compound as both Te and I are non metals. D: Rb is a metallic structure 11 The trends in two physical properties of the elements Na, Mg, Al, Si, P and S are shown in the following graphs. Which of the following illustrates the correct physical property for the corresponding graphs above? Graph 1 Graph 2

Graph 1 Graph 2 A melting point electrical conductivity B 1st ionisation energy electrical conductivity C melting point 1st ionisation energy D 1st ionisation energy melting point Ans: C Graph 1: The melting point increases from Na to Al as the metallic bonding is stronger. Si has the highest melting point as it is a giant covalent lattice which requires the largest amount of energy to overcome the strong network of Si-Si bond. S8 and P4 are simple covalent molecule. As the number of elec trons for S 8 increases, the id -id increases, hence, the melting point increases. Graph 2: Across the period, nuclear charge increases while the increase in shielding effect is insignificant as electrons are added to the same shell. The effective nuclear charge increases, hence, the 1 st ionisation energy increases. However, the first ionisation energy for A l is lower than expected because less energy is needed to remove the 3p electron which is further away from nucleus and experience additional shielding from 3s electrons. 12 Use of the Data Booklet is relevant for this question. Which of the following statements is correct for Group 2 elements and its compounds? A Magnesium is kept in oil as it is more reactive while barium is kept in the open. B Barium reacts with chlorine more spontaneously than magnesium as it has a higher reducing power. C The rate of decomposition is slower for strontium carbonate than barium carbonate. D The volume of CO2 produced is the same when the same mass of strontium carbonate and bariu