2019 CJC Prelim H2 Chem P1 ANS

1 CANDIDATE NAME CLASS 2T CHEMISTRY 9729/01 Paper 1 Multiple Choice Tuesday 3 September 2019 1 hour Additional Materials: Multiple Choice Answer Sheet Data Booklet READ THESE INSTRUCTIONS FIRST Write in soft pencil. Do not use staples, paper clips, glue or correction fluid. Write your name, class and NRIC/FIN number on the Answer Sheet in the spaces provided. There are thirty questions on this paper. Answer all questions. For each question there are four possible answers A, B, C and D. Choose the one you consider correct and record your choice in soft pencil on the separate Answer Sheet. Read the instructions on the Answer Sheet very carefully. Each correct answer will score one mark. A mark will not be deducted for a wrong answer. Any rough working should be done in this booklet. The use of an approved scientific calculator is expected, where appropriate. Catholic Junior College JC 2 Preliminary Examinations Higher 2 WORKED SOLUTIONS

2 9729/01/CJC JC2 Preliminary Examination 2019 1 In a titration experiment, 15 cm3 of 0.10 mol dm−3 phosphorous acid, H3PO3 was found to react with 10 cm3 of 0.30 mol dm−3 sodium hydroxide. Using this information, deduce the formula of the salt formed in this neutralisation process. A NaH2PO3 C Na3PO3 B Na2HPO3 D Na3PO4 Concept: MCS, Acid-base reaction Answer: B Amount of H3PO3 used in experiment = 0.015 x 0.10 = 1.50 x 10-3 mol Amount of NaOH neutralised = 0.010 x 0.30 = 3.00 x 10-3 mol H3PO3 ≡ 2 NaOH 2 mol of NaOH neutralise 2 mol of H+ 1 mol of H+ is left unreacted in 1 mol H3PO3 (since H3PO3 ≡ 3H+) Salt formed contains 1 mol of H+ 2 50 cm3 of a mixture of ethene and propane gas were exploded in excess oxygen. The volume of the residual gases was found to be 200 cm3. On being shaken with potassium hydroxide, the final volume was found to be 90 cm3. What is the composition of the mixture? (All volumes are measured at r.t.p) volume of ethene volume of propane A 10 40 B 20 30 C 30 20 D 40 10 Concept: MCS, calculations involving volume of gases (involving hydrocarbons) Answer: D Let vol of ethene (C2H4) be x. vol of propane (C3H8) = 50 - x Vol of CO2 gas formed in total = 2x + 3(50 - x) = 150 - x Change in vol of residual gases after passing through KOH = vol of CO2 formed = 200 – 90 = 110 cm3 Hence, 150 – x = 110 x = 40 cm3 Vol of ethene = 40 cm3 ; vol of propane = 10 cm3

3 9729/01/CJC JC2 Preliminary Examination 2019 [Turn over 3 Plutonium-239 is a radioactive substance that emits a constant stream of –particles which are similar to the nucleus of 4He. Rubidium-87 is another radioactive substance that emits –particles which can be considered as electrons. A small amount of Plutonium-239 and Rubidium -87 are separately placed in an ionisation chamber to emit a constant stream of radiation and the emitted particles are pa