2019 IB2 HCIS HL Prelim Paper 3

- 1 - Turn over PRELIMINARY EXAMINATION International Baccalaureate 2 Chemistry Higher level Paper 3 Wednesday 4 September 2019 1 hour 15 minutes Candidate name Candidate session number Class Instructions to candidates • Write your candidate name and session number in the boxes above. • Do not open this examination paper until instructed to do so. • Answer all questions. • Answers must be written within the answer boxes provided. • A calculator is required for this paper. • A clean copy of the chemistry data booklet is required for this paper. • The maximum mark for this examination paper is [45 marks]. Section A Questions Answer all questions. 1 Section B Questions Answer all of the questions from the option. Option D – Medicinal chemistry 2‒5 For Examiner’s Use Section A / 15 Section B / 30 Total / 45 12 pages © Hwa Chong International School 2019

- 2 - Turn over Section A Answer all questions. Write your answers in the boxes provided. 1. Rhubarb, spinach and beet are example of plants with high oxalate –content foods. Oxalic acid, H2C2O4 and its salts occur as end‒products of metabolism in these plants. Consuming these plants may have some adverse effects in our bodies. The oxalate ion (C 2O42‒) binds with primarily calcium and can cause stone formation in the urinary tract. However to reduce the oxalate content, soaking these plants in hot water may possibly reduce the oxalate content by action of leaching. The solution containing these ions can then be quantitatively determined. Method s like redox titration with potassium pe rmanganate, KMnO4, can be used to determine the amount of oxalate ion in plants. The redox reaction between oxalate and permanganate ion is shown as below: 2MnO4‒ + 16H+ + 5C2O42‒ → 2Mn2+ + 8H2O + 10CO2 (a) (i) Suggest a plausible research question for the study mentioned above. [1] ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. (ii) Identify two controlled variables in the experiment above. [2] ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. (This question continues on the following page)

- 3 - Turn over (Question 1 continued) (b) The standard solution of standard KMnO 4 was prepared fresh and kept in a dark bottle and the burette and flask w ere covered with aluminium foil. This was to minimise the decomposition of KMnO4 by sunlight. Comment how this can affect the accuracy of the experiment and explain how the volume of titre could be affected if one fails to do so. [2] ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ……………………………………………………………………………………………