2021 DHS H2 Prelim Paper 3_Solutions

© 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 33 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] 0 in Cl2 to –1 in NaCl and +1 in NaClO Disproportionation (ii) Write the balanced equation for the reaction occurring in (a)(i). [1] 2NaOH + Cl2 ® NaCl + NaClO + H2O [2] Shape: Trigonal pyramidal AND Bond angle: 107° (iv) Explain why fluorine does not undergo a similar reaction with aqueous sodium hydroxide to produce NaFO3. [1] Fluorine is a period 2 element and does not have vacant low-lying d orbitals to expand its octet structure to form FO3-. (v) Describe and explain the relative volatility of Cl2 and I2. [2] Both are simple molecular substances with weak instantaneous dipole- induced dipole interaction between molecules. Cl2 has smaller electron cloud size / smaller number of electrons and hence less polarisable electron cloud. Smaller amount of energy is needed to overcome these weaker id-id interactions in Cl2. Hence Cl2 is more volatile than I2. O O O Cl –

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] NaOH(aq), heat (under reflux) (c) Lysine and a