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] ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. (c) After soaking the spinach in hot water for a period of time, the solution containing oxalate ions (extracted from 500.0 g of spinach) was transferred to a 250.0 cm3 standard volumetric flask and the solution was made up to 250.0 cm3 using tap water. White solid appeared and was observed to settle at the bottom of the flask. 25.0 cm 3 of standard oxalate solution was then pipetted and titrated against 0.001 mol dm‒3 of KMnO4. The average titre of 23.50 cm3 of KMnO4 was determined. (i) Calculate the amount of oxalate ions in 25.0cm3 of oxalate ion. [2] ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. (This question continues on the following page)

- 4 - Turn over (Question 1 continued) (ii) State one assumption in your calculation and h ence determine the concentration (ppm) of oxalate ions (C2O42‒) in 500.0 g of spinach. [2] ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. (iii) The solubilities of some oxalate salts are given below. Oxalate salt Concentration (g dm‒3) MgC2O4 12.5 Na2C2O4 26.9 CaC2O4 0.0067g Justify the identity of the white solid formed in (c). [2] ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. (iv) The formation of the white solid is a systematic limitation in this experiment. Suggest an improvement to overcome this. [1] ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. (This question continues on the following page)

- 5 - Turn over (Question 1 continued) (d) In another experiment, oxalate ion was complexed with the i ron (II) ion to form a yellow solution. The concentration of oxalate ions in the resulting solution is then determined from a calibration curve, which is plotted by measuring the light absorbance of standard solutions. (i) Deduce the relationship between absorbance and concentration. [1] ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. (ii) By interpolation of the graph above, determine the c oncentration of oxalate ion, C2O42‒ , when the absorbance measured is 0.08 A. [2] ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. Concentration of C2O42‒/ mol dm‒3

- 6 - Turn over Section B Answer all of the questions. Write your answers in the boxes provided. Option D – Medicinal chemistry 2. Carbamazepine, C15H17N2O, sold under the trade name Tegretol, is used primarily in the treatment of epilepsy and neuropathic pain . It is classified as a narrow therapeutic index drug. Common adverse effects include drowsiness, dizziness, headaches and migraines, motor coordination impairment, nausea, vomiting, and/or constipation. Synergistic effects with a lcohol while taking carbamazepine may lead to enhanced depression of the central nervous system. Carbamazepine (a) Deduce the IHD of Carbamazepine. [1] ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. (b) Comment on the solubility of the drug. [1] ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. (Option D continues on the following page)

- 7 - Turn over (Option D, question 2 continued) (c) (i) Carbamazepine is tested by injection into mice to establish its LD50 and ED50 values. Distinguish between the two terms. [2] ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. (ii) State the significance of the term “therapeutic index” in drug administration. [1] ………………………………………………………………………………………………………………. ………………………………………………………………………………………………………………. (d) Describe the term “synergistic effect”. [1] ………………………………………………………………………………………………………………. ………………………………………………………………………