2022 YIJC H2 CHEM PRELIM P3 QP

©YIJC [Turn over YISHUN INNOVA JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CG INDEX NO CHEMISTRY Paper 3 Free Response Candidates answer on the Question Paper. Additional Materials: Data Booklet 9729/03 12 September 2022 2 hours READ THESE INSTRUCTIONS FIRST This document consists of 31 printed pages and 1 blank page For Examiner’s Use Section A 1 / 17 2 / 18 3 / 25 Section B 4 or 5 / 20 Penalty units significant figures Overall / 80 Write your name, class and index number on all the work you hand in. Write in dark blue or black pen on both sides of the paper. You may use an 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. If additional space is required, you should use the pages at the end of this booklet. The question number must be clearly shown. Section A Answer all the questions. Section B Answer one question. 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.

2 ©YIJC [Turn over Section A Answer all the questions in this section. 1 (a) Describe and explain the trend in the thermal stability of the hydrogen halides, HCl, HBr and HI. Include an equation for the thermal decomposition reaction in your answer. [3] (b) Alkanes are generally considered to be unreactive compounds, showing an inertness to common reagents such as NaOH, H2SO4, and K2Cr2O7. (i) Suggest a reason why these reagents do not react with an alkane such as propane. [1] Propane can be converted into 2-chloropropane when it reacts with chlorine in ultraviolet (UV) light. (ii) Describe the mechanism of the reaction between propane and chlorine in UV light. [3]

3 ©YIJC [Turn over (c) (i) Define the term lattice energy. [1] (ii) Use the data in Table 1.1, together with data from the Data Booklet, to calculate a value for the lattice energy of silver iodide, AgI(s). Show your working. Table 1.1 value / kJ mol−1 electron affinity of iodine, I(g) + e− → I−(g) −295 enthalpy change of sublimation of iodine molecules, I2(s) → I2(g) +62 standard enthalpy change of atomisation of Ag(s) +285 standard enthalpy change of formation of AgI(s) −62 [3]

4 ©YIJC [Turn over (d) Air bags in car inflate rapidly during an accident to protect the front passengers. The air bag contains sodium azide, NaN3, silicon dioxide, SiO2, and potassium nitrate, KNO3. On impact, three reactions take place. The sodium azide first decomposes to sodium and nitrogen. 2NaN3(s) → 2Na(s) + 3N2(g) The nitrogen formed inflates the air bag while the sodium formed reacts with potassium nitrate to form sodium oxide, potassium oxide and additional nitrogen gas, which may be used to fill the air bag. Potassium oxide and sodium oxide then react with silicon dioxide to form harmless metal silicates. K2O(s) + Na2O(s) + SiO2(s) → K2Na2SiO4(s) (i) Write an equation, with state symbols, for the reaction between sodium and potassium nitrate. [1] (ii) Calculate the mass of sodium azide needed to inflate an air bag of capacity 60 dm3 at room temperature and pressure. [2] (iii) To determine the amount of sodium azide in an impure sample, the azide present is first reacted with excess iodine. 2N3− + I2 → 3N2 + 2I − The amount of unreacted iodine is then titrated with a standard solution of sodium thiosulfate. I2 + 2S2O32− → 2I− + S4O62− 0.120 g of an impure sample of sodium azide was dissolved in water. The mixture was reacted with 25.0 cm3 of 0.050 mol dm−3 of aqueous iodine. The excess iodine was found to require 23.10 cm 3 of 0.040 mol dm −3 aqueous sodium thiosulfate for reaction. Calculate the percentage purity of sodium azide in the sample. [3]

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6 ©YIJC [Turn over 2 (a) Ammonia is manufactured by the following reaction. equation 2.1 N2(g) + 3H2(g) ⇌ 2NH3(g) The value of the equilibrium constant, Kp, measured at two different temperatures is shown in Table 2.1. Table 2.1 temperature / K Kp / atm−2 600 1.33 × 10−2 750 1.33 × 10−4 (i) Write the expression for the equilibrium constant, Kp, for this reaction. [1] (ii) A plant is designed to convert, at equilibrium, 50% of the reactants into ammonia. Assuming that the reactants are a mixture of N 2 and H2 in a 1 : 3 ratio by volume, calculate the total equilibrium pressure necessary to bring about a 50% conversion at • 600 K, and • 750 K. [2] (iii) Discuss the relative advantage and disadvantage of using plants designed to run at 600 K instead of 750 K. [2] Theory shows that Kp varies with temperature according to the equation below. log10 Kp (at temperature T1) Kp (at temperature T2) = −∆H 2.30R ( 1 T1 − 1 T2 ) where: T1 and T2 are the temperatures in Kelvins, H is the enthalpy change of the reaction, R is the molar gas constant. (iv) Use the data in Table 2.1, together with data from the Data Booklet, and to calculate the enthalpy change, H, in kJ mol−1, for the reaction in equation 2.1. [1] (v) The standard enthalpy change of formation of ammonia is −46 kJ mol−1, given that H for the reaction in equation 2.1 to be −92 kJ mol−1. Suggest one reason why this differs from the value calculated in (iv). [1]

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8 ©YIJC [Turn over (b) The Kb values of three bases, at 25 oC, are shown in Table 2.2. Table 2.2 base formula Kb / mol dm−3 ammonia NH3 1.8 × 10−5 ethylamine CH3CH2NH2 4.5 × 10−4 phenylamine 7.4 × 10−10 (i) Calculate the pH of 0.25 mol dm−3 solution of ethylamine. [2] (ii) Explain the relative magnitudes of the Kb values in Table 2.2. [2] (iii) Explain why amides, RCONH2, are neutral, rather than basic. [1]

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10 ©YIJC [Turn over (c) Nitrous acid, HNO 2, can be used to react with aminoalcohol to form an enlarged cycloketone via the Tiffeneau-Demjanov Rearrangement, as shown below. Methylenecyclopentane can be used to synthesise cyclohexanone by the four-step route shown in Fig. 2.1. Fig. 2.1 State the reagents and conditions required for step 1, 2 and 3 and suggest structures for the organic compounds L, M and N.