YIJC 2023 H2 Chem Prelim P1 Worked Solutions (1)

©YIJC [Turn over YISHUN INNOVA JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME TEACHER’S COPY CG INDEX NO CHEMISTRY Paper 1 Multiple Choice Additional Materials: Multiple Choice Answer Sheet Data Booklet 9729/01 15 September 2023 1 hour READ THESE INSTRUCTIONS FIRST Write in soft pencil. Do not use staples, paper clips, highlighters, glue or correction fluid/tape. Write your name and class on the Answer Sheet in the spaces provided unless this has been done for you. 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. Read the instructions on the 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. The use of an approved scientific calculator is expected, where appropriate. This document consists of 16 printed pages.

©YIJC [Turn over 2 1 A medal has a total surface area of 150 cm2. It is evenly coated with silver by electrolysis. Its mass increases by 0.216 g. How many atoms of silver are deposited per cm2 on the surface of the medal? A 8.0 x 1018 B 1.8 x 1019 C 8.7 x 1020 D 1.2 x 1021 Answer: A Amount of Ag = 0.216 / 107.9 = 2.00185 x 10-3 mol Number of Ag = 2.00185 x 10-3 x 6.02 x 1023 = 1.20511 x 1021 Number of atom per cm2 = 1.20511 x 1021 / 150 = 8.03 x 1018 2 Which gas would behave most like an ideal gas under room conditions? A ammonia B helium C krypton D nitrogen Answer: B Ideal gas should have negligible intermolecular forces of attraction. Ammonia has hydrogen bonding which has the strongest IMF. Between helium, krypton and nitrogen, helium has the smallest electron cloud size so weakest id-id.

©YIJC [Turn over 3 3 In two separate experiments a beam of protons and a beam of He2+ 2 4 particles, travelling at the same velocity, pass through an electric field as shown. Which statements are correct? 1 Both beams are deflected in the same direction. 2 The proton beam travels in a straight path towards the negatively charged plate. 3 The protons are deflected to a larger extent than the He2+ 2 4 particles. A 1 and 2 B 1 and 3 C 2 and 3 D 1 only Answer: B Statement 1 is correct. Both protons and He2+ 2 4 particles are positively charged, they will be deflected in the same direction, towards the negatively charged plate. Statement 2 is incorrect. The proton beam travels in an angle similar to a circular path after deflection. Statement 3 is correct. Since 𝜃 ∝ 𝑒 𝑚, protons have charge/mass ratio of 1 whereas He2+ 2 4 particles have a charge/mass ratio of ½ , protons will have a larger angle of deflection. 4 The table shows some properties of four substances. Which substance could be potassium iodide? Melting point of solid / °C Electrical conductivity when molten A −66 poor B −39 good C 680 good D 1600 poor

©YIJC [Turn over 4 Answer: C Potassium iodide has a giant ionic structure hence it will have a high melting point due to strong ionic bond and high lattice energy. The ions can also act as mobile charge carrier in molten state hence it will have good electrical conductivity. 5 A carbon monoxide molecule, CO, has three bonds between the carbon atom and the oxygen atom. Which features are present in one CO molecule? 1 Three lone pairs of electrons 2 A co-ordinate bond from oxygen to carbon 3 Two  bonds A 1 and 2 B 2 and 3 C 1 and 3 D 1, 2 and 3 Answer: B 1 is incorrect as there’s only two lone pairs of electrons. 2 is correct as the dative bond allows both carbon and oxygen to achieve 8 electrons around the atom. 3 is correct as CO bond has 1 sigma and the next two are pi bonds

©YIJC [Turn over 5 6 The reaction of manganate(VII) ions with ethanedioate ions in acid solution may be represented by the following equation. 2MnO4–(aq) + 16H+(aq) + 5C2O42–(aq) → 2Mn2+(aq) + 8H2O(l) + 10CO2(g) The graph shows concentration of manganate(VII) ions against time for this reaction. What does the shape of the graph suggest about this reaction? A The rate of reaction decreases with time. B The reaction is endothermic. C The reaction shows first order kinetics. D The reaction is catalysed by a product. Answer: D The gradient of the graph increases as time increases indicating that the products formed catalyse the reaction. Hence the products are present in the rate equation. [MnO4−] 0 time

©YIJC [Turn over 6 7 The graph shows the results of an investigation of the initial rate of hydrolysis of casein by the enzyme trypsin. In the experiments, the initial concentration of casein was varied but that of trypsin was kept constant. Which conclusions can be deduced from these results? 1 When [casein] is high, the rate is independent of [trypsin]. 2 When [casein] is high, the rate is independent of [casein]. 3 When [casein] is low, the rate is first order with respect to [casein]. A 1, 2 and 3 B 1 and 2 C 2 and 3 D 1 only Answer: C The relationship between reaction rate and [trypsin] cannot be deduced from the graph. initial reaction rate [casein] 0 At high [casein]: horizontal straight line; rate is independent of [casein]  zero order w.r.t. [casein] At low [casein]: straight line through origin; rate is directly proportional to [casein]  first order w.r.t. [casein] initial reaction rate [casein] 0

©YIJC [Turn over 7 8 An equilibrium is set up, in a vessel at constant temperature and atmospheric pressure, according to the following reaction. 2NO2(g) ⇌ N2O4(g) The vessel is attached to a plunger which can alter the pressure inside the vessel. At a time t, the plunger is pushed in quickly to increase the pressure and an new equilibrium is established. The temperature is maintained constant throughout. Which graph shows the change in partial pressure of N2O4, pN2O4 , during this process? A B C D Answer: B At t, when compressed (vol decrease while temp is constant), partial pressure of N2O4 will increase. As the pressure of the system increases, by Le Chateliers’ Principle, position of above equilibrium will shift to the right to favor the formation of fewer gaseous molecules, so as to decrease the pressure. Hence, more N2O4 will be produced, resulting in increasing partial pressure of N2O4 after t. t time time t time t time t

©YIJC [Turn over 8 9 An experiment was conducted to determine the efficiency of the heating of a can of water using a spirit burner. The following data were recorded: Mass of ethanol burnt = m g Change in temperature of water = ∆T oC You are also given that: Relative molecular mass of ethanol = 46.0 Enthalpy change of combustion of ethanol = –1371 kJ mol−1 Specific heat capacity of water = c J g−1 K−1 Which expression below gives the efficiency of this heating process? A 300 × c × ∆T × 46.0 m × 1371 × 1000 × 100% B m × c × ∆T