2021 SAJC Prelim P2 Question

ST ANDREW’S JUNIOR COLLEGE JC2 Preliminary Examinations Higher 2 CANDIDATE NAME CLASS 2 0 S CHEMISTRY Paper 2 Structured Questions Candidate answer on the Question Paper. Additional Materials: Data Booklet 9729/02 1 September 2021 2 hours READ THESE INSTRUCTIONS FIRST Write your name and class on all the work you hand in. Write in dark blue or black pen. You may use a HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Answer all questions in the spaces provided on the Question Paper. The use of an approved scientific calculator is expected, where appropriate. A Data Booklet is provided. 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 19 printed pages. For Examiner’s Use Q1 9 Q2 9 Q3 24 Q4 20 Q5 13 Total 75

2 Answer all questions in the spaces provided. 1 (a) Fig. 1.1 shows a sketch of the logarithm of the first ten ionisation energies, log (IE), of element A against the number of electrons removed. Fig. 1.1 (i) Write an equation for the second ionisation energy of element A. [1] ______________________________________________________________ 0 1 2 3 4 5 6 7 8 9 10 11 log (IE) Number of electrons removed

3 (a) (ii) Explain the following features of Fig. 1.1.  the general trend in ionisation energy shown in the graph  the significant jump in values from the 5th to the 6th ionisation energy [4] ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ (iii) Element A is in Period 3. Identify element A using information from Fig. 1.1 and complete it s electronic configuration. [1] Element A is _____________ Electronic Configuration: 1s2 2s2 _______________

4 (b) Sulfur is another element in Period 3. It forms covalent bonds with other elements in covalent compounds such as SO2, SO3, SCl2. (i) Describe a covalent bond. [1] ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ (ii) Predict the intermolecular force which exists between SO3 molecules. Explain how this force arises. You may use diagrams where appropriate to illustrate your answer. [2] ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ [Total: 9 marks]

5 2 Esters are commonly used as artificial flavourings in food products such as cakes and sweets. However, the shelf life of acidic foods containing esters are relatively short as esters are prone to acid-catalysed hydrolysis. The kinetics of the acid -catalysed hydrolysis of the ester , methyl propanoate, CH3CH2CO2CH3, was investigated in an experiment. (a) Write a balanced equation for the hydrolysis of methyl propanoate. [1] ___________________________________________________________________ (b) 0.200 mol of ester was hydrolysed by heating with water and hydrochloric acid catalyst in a 1 dm 3 mixture. In a second experiment, hydrochloric acid was replaced with sulfuric acid of the same concentration. When the reaction is complete, 0.200 mol of propanoic acid is obtained. The following results were obtained. 0.000 0.020 0.040 0.060 0.080 0.100 0.120 0.140 0.160 0.180 0.200 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 time / s [CH3CH2COOH] / mol dm–3 Experiment 1 HCl catalyst Experiment 2 H2SO4 catalyst

6 (b) (i) Based on the results obtained, show that the reaction is first order with respect to the ester and first order with respect to H+ ions. [4] ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ (ii) State the units of the rate constant, k. [1] ______________________________________________________________

7 (c) With the aid of a sketch of the Boltzmann distribution, explain how an increase in temperature changes the rate of ester hydrolysis. [3] ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ [Total: 9 marks]

8 3 Scuba diving is an extreme sport where divers carry their own source of breathing gas to explore the open sea. Table 3.1 lists the compositions by volume of two breathing gases used by scuba divers. Table 3.1 Mixture Composition by volume Nitrox 32% oxygen, 68% nitrogen Heliox 21% oxygen, 79% helium (a) (i) State one assumption of the kinetic theory as applied to an ideal gas. Hence, deduce, with reasons, whether Nitrox or Heliox shows greater devi ation from ideal gas behaviour. [2] ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ (ii) Use of the Data Booklet is relevant to this question. A canister of breathing gas has a density of 435 g m–3 at standard temperature and pressure (s.t.p). Calculate the average molar mass of the mixture. Hence, with reference to Table 3.1, deduce the identity of the breathing gas. [3]

9 (b) At sea level, the atmospheric pressure is 1 atm. In the sea, there is an increase in pressure of 1 atm for every 10 m of depth below the surface. For example, at 10 m, the pressure on the diver's body is 2 atm and at 20 m, the corresponding pressure is 3 atm. When a diver inhales from the gas canister, the air that enters the diver's lungs is at the surrounding pressure. For safety reasons, divers should not inhale oxygen at partial pressures greater than 1.3 atm, as this may le