2023 DHS H2 Chem Prelim Paper 3 QP

© DHS 2023 9729/03 [Turn over DUNMAN HIGH SCHOOL Preliminary Examination Year 6 H2 CHEMISTRY Paper 3 Free Response Questions Candidates answer on the Question Paper. Additional Materials: Data Booklet 9729/03 21 September 2023 2 hours READ THESE INSTRUCTIONS FIRST Write your centre number, index number, name and class at the top of this page. Write in dark blue or black pen. 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 questions. Section B Answer one question. A Data Booklet is provided. The use of an approved scientific calculator is expected, where appropriate. The number of marks is given in brackets [ ] at the end of each question or part question. Name: Centre/Index Number: Class: For Examiner’s Use Section A 1 20 2 15 3 25 Section B 4 / 5 20 Total 80 This document consists of 25 printed pages and 1 blank page. This document consists of 28 printed pages.

2 © DHS 2023 9729/03 Section A Answer all the questions in this section. 1 (a) Group 2 salts, such as carbonates, decompose when heated. Table 1.1 shows information of some Group 2 salts that undergo thermal decomposition. Table 1.1 Group 2 salt thermal decomposition temperature / °C MgCO3 350 CaCO3 825 (i) Explain the difference in thermal decomposition temperature of MgCO 3 and CaCO3. [2] (ii) Hence predict the thermal decomposition temperature for SrCO3. [1] (iii) Write an equation for the thermal decomposition of CaCO 3. Include state symbols in your answer. [1] (iv) State and explain the sign of S for the thermal decomposition of CaCO 3. Hence explain how spontaneity of the reaction changes as temperature increases. [2] (v) Outline a suitable experiment to verify that the thermal decomposition of a sample of Mg(OH)2 is complete. No details regarding use of specific glassware are required. [2] ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..……………….

3 © DHS 2023 9729/03 [Turn over ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. (b) Group 2 carbonates are sparingly soluble in water. Table 1.2 shows the solubility product, Ksp, of two Group 2 carbonates. Table 1.2 Group 2 carbonate Ksp MgCO3 2.61 × 10–3 CaCO3 5.83 × 10–5 (i) Write an expression for Ksp of MgCO3, giving its units. [1] (ii) Describe and explain how the solubility of MgCO 3 is affected by the addition of ethanoic acid. [2] Excess solid magnesium nitrate and calcium nitrate were added to a solution containing carbonate ions. The mixture was stirred and left to equilibrate at room temperature. (iii) Calculate the [Mg2+]/[Ca2+] ratio in the resulting mixture. [1] ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..……………….

4 © DHS 2023 9729/03 (c) Magnesium is also used in the pinacol coupling reaction. A new C –C bond is formed between two carbonyl compounds, as shown in Fig. 1.1. R'R O 2 (i) Mg (ii) dilute acid OH R R' OH R' R Fig. 1.1 (i) When butanone undergoes the pinacol coupling reaction, a mixture of 3 stereoisomers are formed. Draw the structure of the product that does not rotate plane-polarised light, showing the stereochemistry of the molecule clearly. [1] (ii) Phenaglycodol is a sedative. It can be synthesised from compounds P and Q using the pinacol coupling reaction. Cl OH OH Phenaglycodol Suggest possible structures for P and Q. [2] ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………

5 © DHS 2023 9729/03 [Turn over (d) Compound R, C 8H8O2, reacts with Fehling’s reagent and aqueous bromine. It is also soluble in NaOH(aq). When R is heated with acidified potassium manganate(VII), C8H8O3, is first formed. Further heating produces 4 - hydroxybenzoic acid. For each reaction, state the type of reaction described and explain what the information tells you about the functional groups present in R. Hence suggest a possible structure for R. [5] ………………………………………………………………………..………………………. ………………………………………………………………………..………………………. ………………………………………………………………………..………………………. ………………………………………………………………………..………………………. ………………………………………………………………………..………………………. ………………………………………………………………………..………………………. ………………………………………………………………………..………………………. ………………………………………………………………………..………………………. ………………………………………………………………………..………………………. ………………………………………………………………………..………………………. ………………………………………………………………………..………………………. ………………………………………………………………………..………………………. ………………………………………………………………………..………………………. ………………………………………………………………………..………………………. ………………………………………………………………………..………………………. ………………………………………………………………………..………………………. ………………………………………………………………………..………………………. ………………………………………………………………………..………………………. ………………………………………………………………………..………………………. ………………………………………………………………………..………………………. ………………………………………………………………………..………………………. ………………………………………………………………………..………………………. ………………………………………………………………………..………………………. ………………………………………………………………………..………………………. [Total: 20]

6 © DHS 2023 9729/03 2 (a) (i) State the two main assumptions of ideal gases. [1] (ii) Explain why a real gas will deviate more from ideality at a lower temperature. [1] ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. ………………………………………………………………………..………………. (b) Pure hydrogen iodide, HI, partially dissociates into hydrogen and iodine as shown in the equation below. 2HI(g) ⇌ H2(g) + I2(g) The reaction was carried out at 500 K. At the start of the reaction, 9.0 × 10–4 mol of HI were introduced