CJC 2019 Promo Paper 1 _ 3 Answers

[Turn over 9729/CJC JC1 Promotional Exam 2019 CANDIDATE NAME CLASS 1T CHEMISTRY 9729/01 & 03 Paper 1 Multiple Choice (30 minutes) Wednesday 2 October 2019 Paper 3 Free Response (1 hour) 1 hour 30 minutes Additional Materials: Multiple Choice Answer Sheet Data Booklet READ THESE INSTRUCTIONS FIRST Do not use staples, paper clips, highlighters, glue or correction fluid. Write and/or shade your name, NRIC / FIN number and class on the Multiple Choice Answer Sheet in the spaces provided. For Paper 1, there are fifteen questions. 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 Multiple Choice 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. For Paper 3, write your answers using the writing papers provided. Write in dark blue or black pen on both sides of the paper. Start each question on a fresh sheet of paper. You may use an HB pencil for any diagrams or graphs. The use of an approved scientific calculator is expected, where appropriate. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. This document consists of 11 printed pages and 1 blank page. Catholic Junior College JC1 Promotional Examinations Higher 2 Worked Solutions and ANSWERS

2 [Turn over 9729/CJC JC1 Promotional Exam 2019 Paper 1 1 Which of the following statements is not true? A One mole of water contains 2 moles of hydrogen atoms. B One mole of chlorine gas contains 6.02 x 1023 chlorine atoms. C One mole of ammonia has a mass of 17.0 g. D One mole of sodium chloride contains 1.204 x 1024 ions. 2 In an experiment, 2 moles of an aqueous metallic salt reacted exactly with 1 mole of aqueous sodium sulfite, Na2SO3. The half-equation for oxidation of sulfite ion, SO32- is shown below. SO32– (aq) + H2O(l) → SO42–(aq) + 2H+(aq) + 2e– If the original oxidation number of the metal in the salt was +5, what would be the new oxidation number of the metal? A +1 B +2 C +3 D +4 Ans: D M5+ : SO32- = 2:1 (given) So, 2M5+ ≡ SO32- ≡ 2e- M5+ ≡ e- So, M5+ + e- → Mn+ n = 4, new oxidation number of the metal is +4 Ans: B A True One mole of water, H2O, has 2 moles of hydrogen atoms. B Not True One mole of chlorine gas contains 2 x 6.02 x 1023 chlorine atoms. C True Molar mass of ammonia is 14.0 x 3(1.0) = 17.0 g/mol. D True. Each mole of sodium chloride contains 2 x 6.02 x 10 23 = 1.204 x 10 24 of Na + and Cl– ions.

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