2021 DHS H2 Prelim Paper 3 Questions

© DHS 2021 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 22 September 2021 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 20 3 20 Section B 4 / 5 20 Total 80 This document consists of 28 printed pages.

2 © DHS 2021 9729/03 Section A Answer all the questions in this section. 1 (a) Aqueous sodium hydroxide reacts with halogens, such as chlorine, under different conditions, to form NaClO and NaClO3. At 10 °C, aqueous sodium hydroxide reacts with chlorine to produce NaCl and NaClO. (i) State the change(s) in oxidation state of chlorine when chlorine is reacted with aqueous sodium hydroxide at 10 °C. Hence, name the type of reaction that occurred. [1] (ii) Write the balanced equation for the reaction occurring in (a)(i). [1] (iii) Draw the structure of ClO3– ion, stating its shape and bond angle. [2] (iv) Explain why fluorine does not undergo a similar reaction with aqueous sodium hydroxide to produce NaFO3. [1] (v) Describe and explain the relative volatility of Cl2 and I2. [2] …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. ………………………………………………………………………………………….

3 © DHS 2021 9729/03 [Turn over …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. (b) Venturamide A is a cyclic peptide with anti-malarial activity. It has the following structure. Suggest reagents and conditions for the basic hydrolysis of Venturamide A and draw the structures of the organic products. Assume that the 2 rings, and , are inert in the reaction. [3] …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. N H N N NH NH S O S N O O O

4 © DHS 2021 9729/03 (c) Lysine and alanine are naturally–occurring amino acids. Lysine Alanine (i) Write an equation to show how the zwitterionic form of lysine can remove small amounts of H+. [2] (ii) Draw the structures of the major species present in a solution of the lys–ala dipeptide at each of the following pH values at room temperature. • pH 1 • pH 10 [2] (iii) Briefly explain why the α–NH2 group of lysine is less basic than its side–chain –NH2 group. [1] …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. O OH NH2 NH2 pKa1 = 2.18 pKa2 = 8.95 pKa3 = 10.53 O OH NH2 pKa1 = 2.35 pKa2 = 9.87

5 © DHS 2021 9729/03 [Turn over (d) Compound X, C8H16Cl2, is a symmetrical molecule which has two chiral carbon centres. When compound X is heated under reflux with excess aqueous sodium hydroxide, compound Y, C8H18O2, is formed. The reaction kinetics follows the rate equation, rate = k[X]. Upon heating Y with acidified potassium manganate(VII), no decolourisation is observed. When compound X is heated in a sealed tube in excess ammonia gas, compound Z with the molecular formula C8H20N2 is produced. Deduce the structures of compounds X to Z, giving your reasoning. [5] …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. [Total: 20]

6 © DHS 2021 9729/03 2 (a) Zinc–air batteries have received revived interest recently due to its higher energy density, larger storage capacity and lower production cost as compared to the commonly–used conventional lithium–ion batteries. A zinc-air battery comprises zinc electrode, porous carbon–containing air electrode, an electrolyte and a separation membrane. The electrolyte used is aqueous potassium hydroxide. The zinc–air battery has a standard cell potential of +1.59 V. During discharging, zinc is oxidised to zinc oxide, ZnO, at the zinc electrode according to the following reaction: Zn + 2OH− → ZnO + H2O + 2e− (i) Write the half-equation for the reaction that occurred at the air electrode during discharging. [1] (ii) Using suitable data from the Data Booklet, calculate the E¡ value for the ZnO / Zn electrode. [1] (iii) With reference to your a