CJC 2019 Promo Paper 1 3 Answers

[Turn over 9729/CJC JC1 Promotional Exam 2019 CANDIDATE NAME CLASS 1T CHEMISTRY 9729/01 & 03 Paper 1 Multiple Choice (30 minutes) Wednesday 2 October 2019 Paper 3 Free Response (1 hour) 1 hour 30 minutes Additional Materials: Multiple Choice Answer Sheet Data Booklet READ THESE INSTRUCTIONS FIRST Do not use staples, paper clips, highlighters, glue or correction fluid. Write and/or shade your name, NRIC / FIN number and class on the Multiple Choice Answer Sheet in the spaces provided. For Paper 1, there are fifteen questions. 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. Read the instructions on the Multiple Choice Answer Sheet very carefully. 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. For Paper 3, write your answers using the writing papers provided. Write in dark blue or black pen on both sides of the paper. Start each question on a fresh sheet of paper. You may use an HB pencil for any diagrams or graphs. The use of an approved scientific calculator is expected, where appropriate. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. This document consists of 11 printed pages and 1 blank page. Catholic Junior College JC1 Promotional Examinations Higher 2 Worked Solutions and ANSWERS

2 [Turn over 9729/CJC JC1 Promotional Exam 2019 Paper 1 1 Which of the following statements is not true? A One mole of water contains 2 moles of hydrogen atoms. B One mole of chlorine gas contains 6.02 x 1023 chlorine atoms. C One mole of ammonia has a mass of 17.0 g. D One mole of sodium chloride contains 1.204 x 1024 ions. 2 In an experiment, 2 moles of an aqueous metallic salt reacted exactly with 1 mole of aqueous sodium sulfite, Na2SO3. The half-equation for oxidation of sulfite ion, SO32- is shown below. SO32– (aq) + H2O(l) → SO42–(aq) + 2H+(aq) + 2e– If the original oxidation number of the metal in the salt was +5, what would be the new oxidation number of the metal? A +1 B +2 C +3 D +4 Ans: D M5+ : SO32- = 2:1 (given) So, 2M5+ ≡ SO32- ≡ 2e- M5+ ≡ e- So, M5+ + e- → Mn+ n = 4, new oxidation number of the metal is +4 Ans: B A True One mole of water, H2O, has 2 moles of hydrogen atoms. B Not True One mole of chlorine gas contains 2 x 6.02 x 1023 chlorine atoms. C True Molar mass of ammonia is 14.0 x 3(1.0) = 17.0 g/mol. D True. Each mole of sodium chloride contains 2 x 6.02 x 10 23 = 1.204 x 10 24 of Na + and Cl– ions.

3 [Turn over 9729/CJC JC1 Promotional Exam 2019 3 The first five successive ionisation energies of an element, W, found in Period 3, are as follows: 577, 1820, 2740, 11600, 14800 kJ mol–1 Which statements are consistent with these data? 1 The outer electronic configuration of an atom of W is 3s23p1. 2 There is a large increase between the 3 rd and the 4th ionisation energy because the 4th electron is from an inner principal quantum shell. 3 W forms a chloride with a formula WCl4. A 1 and 2 only B 2 and 3 only C 1, 2 and 3 D 1 only 4 The Valence Shell Electron Pair Repulsion (VSEPR) theory is used to predict the shapes of molecules. Which shape is correctly predicted by VSEPR theory? Number of bonded electron pairs around central atom Number of lone pairs around central atom Shape A 2 1 linear B 2 1 trigonal planar C 3 1 tetrahedral D 3 1 trigonal pyramidal Ans: A W is in Group 13 as there is a sharp increase between the 3rd and 4th IE. Thus, the 4th electron is found in the inner principal quantum shell and W has 3 valence electrons. Since it is in Period 3, W is aluminium. 1 The outer electronic configuration of a Group 13 element is ns2np1. 2 True. Electrons in the inner electron shells experience less shielding effect and are nearer to the nucleus. 3 False. It forms chloride with molecular formula WCl4. Ans: D Concepts: Using VSEPR theory to predict shapes of molecules. Number of bonded electron pairs around central atom Number of lone pairs around central atom shape 2 1 bent 3 1 trigonal pyramidal

4 [Turn over 9729/CJC JC1 Promotional Exam 2019 5 In 1985, a molecular form of carbon, C 60, called buckminsterfullerene, was discovered in the products formed when graphite was vapourised. It exhibits some properties similar to graphite. The structure proposed for the molecule is a roughly spherical collection of atoms in the shape of hexagons and pentagons, very much like a soccer ball. Which one of the following properties is expected of buckminsterfullerene? 1 It burns completely in oxygen to give carbon dioxide gas only. 2 It has a lower melting point compared to graphite. 3 It dissolves in water. A 1 only B 2 only C 1 and 2 only D 1, 2 and 3 only 6 Gases such as helium behave ideally under conditions of high temperature and low pressure. Which of the following gases are very likely to behave ideally under the same conditions? 1 ammonia, NH3 2 hydrogen, H2 3 nitrogen, N2 A 3 only B 1 and 2 only C 2 and 3 only D 1 and 3 only Ans: C 1. C60 + 60O2  60CO2 2. There are weak intermolecular forces between molecules (id-id) of buckminsterfullerene. These need little energy to overcome, so buckminsterfullerene has a low melting point. 3. Buckminsterfullerene contains 60 C atoms and is non polar. Hence it is insoluble in water.

5 [Turn over 9729/CJC JC1 Promotional Exam 2019 7 A student used the apparatus below to heat a can containing 300 g of water. The following data were recorded: Mass of propan-1-ol burnt = m g Change in temperature of water = ΔT oC You are given that: Relative molecular mass of propan-1-ol = 60.0 Specific heat capacity of water = c J g–1 K–1 What is the enthalpy change of combustion, in kJ mol–1, given that the process is 100 % efficient? A − m × c × ∆T × 60 300 C − 300 × c × ∆T × 60 1000 × m B − m × c × ∆T × 60 1000 × 300 D − 300 × c × (∆T + 273) × 60 1000 × m Ans: C Assumptions applied to ideal gas includes negligible intermolecular forces of attractions. 1 NH3 experiences strong hydrogen bonding between molecules and the attraction is not likely to be negligible hence NH3 should not exhibit ideal gas behavior. 2 H2 has only 2 electrons and have very weak instantaneous dipole -induced dipole forces of attraction between molecules which can be considered negligible hence H 2 behaves ideally. 3 N2 has only 14 electrons and hav e also quite weak instantaneous dipole -induced dipole forces of attraction between molecules and should also behave ideally, though less ideal than hydrogen. Furthermore, no options of 2 only. thermometer can containing 300 g of water burner containing propan-1-ol

6 [Turn over 9729/CJC JC1 Promotional Exam 2019 8 Instant heat packs comprise a supersaturated solution of sodium ethanoate and a small flat disc of iron metal embedded in the solution. Pressing the disc will cause the following reaction to occur: CH3CO2Na(aq) + 3H2O(l) → CH3CO2Na.3H2O(s) Which of the following reflects the correct signs of ∆H, ∆S and ∆G for the overall process of the reaction? ∆H ∆S ∆G A + – + B + + – C – + – D – – – Ans: C Amount of heat energy evolved from combustion of propanol = no. of moles of propanol x ∆Hc = 𝑚 60.0 x ∆Hc Heat