ACJC Prelim P2 QP

3 © ACJC 2018 9729/02/Prelim/2018 [Turn over Answer all the questions in the spaces provided. 1 A mixture contains two white solids XCO3 and YSO4 where X and Y could be either magnesium, zinc or barium. The following investigations were carried out to determine the identity of X and Y. (a) When the mixture of solids was treated with excess dilute hydrochloric acid, a colourless gas was evolved and some, but not all, of the mixture dissolved. The resulting mixture was filtered. To the filtrate, dilute aqueous ammonia was added dropwise till in excess. The white precipitate formed was insoluble in excess aqueous ammonia. Deduce the identity of elements X and Y, showing your reasoning clearly. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………. [3] (b) Group 2 carbonates decompose according to the following equation: ZCO 3(s) ZO(s) + CO2(g) element magnesium calcium barium enthalpy change for the reaction, ∆Hr / kJ mol−1 +101 +178 +269 (i) Use the data above to state and explain the trend in the thermal stability of the Group 2 carbonates. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. …………………………………………………………………………………………. ……………………………………………………………………………………… [3]

4 © ACJC 2018 9729/02/Prelim/2018 [Turn over (ii) Lithium carbonate, a Group 1 carbonate, decomposes on heating. Use relevant data from the Data booklet to calculate relative charge densities of the above cations and hence deduce which of the above ∆Hr values in the table is likely to be the nearest to that of lithium carbonate. [2] (c) Patients with digestive tract problems are sometimes asked to take an x-ray after they have swallowed a “barium meal”, consisting of a suspension of BaSO 4 in water. (i) Write an expression for the solubility product, Ksp for BaSO4, including its units. …………………………….………………………………………………………… [2] (ii) The numerical value of Ksp is 1.30 × 10–10. Calculate [Ba 2+(aq)] in a saturated solution of BaSO4. [1] (iii) Although Ba 2+ ions are toxic, the [Ba 2+(aq)] in a saturated solution of BaSO 4 is too low to cause any problems of toxicity. The numerical value of K sp for BaCO3 (5 × 10–10) is not significantly higher than that of BaSO4, but BaCO3 is very poisonous if ingested. Suggest a reason why this might be so. …………………………………………………………………………………………… ……………………………………………………………………………………….. [1]

5 © ACJC 2018 9729/02/Prelim/2018 [Turn over (iv) BaSO4 is commonly prepared in the laboratory by combining aqueous solutions containing Ba2+ and SO42–. Determine if BaSO 4 will form when equal volumes of 2.00 × 10–2 mol dm –3 aqueous Ba(NO3)2 and 4.00 × 10–2 mol dm–3 aqueous Na2SO4 are mixed. [2] [Total: 14]

6 © ACJC 2018 9729/02/Prelim/2018 [Turn over 2 A student conducted two separate electrolysis using inert electrodes under room temperature and pressure. electrolysis reaction electrolyte volume of gas collected at anode / cm3 duration 1 concentrated hydrochloric acid 150 10 minutes 2 aqueous sodium sulfate 37.5 (a) (i) Write the half-equation with state symbols for the reaction occurring at the anode for electrolysis reaction 1. ……………………………………………………………………………………….. [1] (ii) Calculate the current that was used in electrolysis reaction 1. [2] (b) (i) Write the half-equation with state symbols for the reaction occurring at the anode for electrolysis reaction 2. ……………………………………………………………………………………….. [1] (ii) Determine the current used in electrolysis reaction 2. [2] [Total: 6]

7 © ACJC 2018 9729/02/Prelim/2018 [Turn over 3 Sertraline is an antidepressant used to treat depression, obsessive compulsive disorder, post-traumatic stress disorder and related c onditions. This medication can help to improve mood, mental alertness, energy level and sleep pattern for the patients. Sertraline works by helping to restore the balance of serotonin, a neurotransmitter in the brain which regulates anxiety, mood and happiness. A proposed synthesis route of sertraline is shown below. (a) State the reagents and conditions needed for step 1 and draw the structure of compound V in the box above. ………………………………………………………………………………………………. [2] Sertraline compound W compound V

8 © ACJC 2018 9729/02/Prelim/2018 [Turn over (b) Electrophilic substitution takes place in step 3 where AlCl3 acts as a Lewis acid catalyst and reacts with the acyl chloride functional group to generate the electrophile. Write an equation to show the generation of the electrophile and hence draw the mechanism for the reaction that occurs in step 3. You may use R to represent in Sertraline for part (b) and part (d). [3] (c) State the type of reaction taking place in step 4 and draw the structure of compound W in the box above. ………………………………………………………………………………………………. [2]

9 © ACJC 2018 9729/02/Prelim/2018 [Turn over (d) Sertraline exists as a mixture of stereoisomers. Draw the structures of the stereoisomers of Sertraline. [2] [Total: 9]

10 © ACJC 2018 9729/02/Prelim/2018 [Turn over 4 (a) The change in colour from blue to pink of the cobalt complexes has been the basis of cobalt chloride indicator papers for the detection of the presence of water. The two differently coloured cobalt( II) complex ions, Co(H 2O)62+ and CoC l42–, exist together in equilibrium in solution in the presence of chloride ions. This is represented by the equation below. Co(H2O)62+(aq) + 4Cl–(aq) CoCl42–(aq) + 6H2O(l) An experiment is conducted to investigate the