CJC Prelim P1_SOL

1 CHEMISTRY 9729/01 Paper 1 Multiple Choice 29 August 2017 Additional Materials: Multiple Choice Answer Sheet Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, HT group and NRIC/FIN number on the Answer Sheet in the spaces provided. Write in soft pencil. Do not use staples, paper clips, glue or correction fluid. 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. This document consists of 25 printed pages and 1 blank page. Catholic Junior College JC 2 Preliminary Examinations Higher 2 MARK SCHEME

2 9729/01/CJC JC2 Preliminary Examination 2017 For each question there are four possible answers, A, B, C and D. Choose the one you consider to be correct. 1 When an unknown organic compound is burned completely in excess oxygen, 90 cm3 of gaseous products is collected. When cooled to room temperature, the gaseous volume decreased to 50 cm3. A further decrease of 40 cm3 in the gaseous volume was observed when the gaseous mixture is passed through aqueous potassium hydroxide. What is the possible identity of the organic compound? 1 CH2CH2 2 CH3CO2H 3 CH3CH2CH3 4 CH2CHCH2OH A 1 and 3 only B 1 and 4 only C 1, 2 and 4 only D 2 and 4 only Answer: C First reduction of gaseous vol due to cooling  hot H2O(g) has condensed to form H2O(l) at r.t.p.  thus, vol of H2O(g) = 90 – 50 = 40 cm3 Second reduction of gaseous vol due to reaction with KOH(aq)  CO2(g) is an acidic gas and reacts with KOH(aq) via acid-base reaction  vol of CO2(g) = 40 cm3 Thus, CO2(g) : H2O(g) Thus, C : H = 40 : 40 = 1 : 2 = 1 : 1 Thus the organic compound must have a ratio C : H = 1: 2. 1 CH2CH2  C2H4  correct 2 CH3CO2H  C2H4O2  correct 3 CH3CH2CH3  C3H8  incorrect 4 CH2CHCH2OH  C3H6O  correct Concept: MCS: rxn stoichiometry, molar volume of gas at r.t.p, Start with volume of CO2 given and use the equation to work out the mole ratio.

3 9729/01/CJC JC2 Preliminary Examination 2017 [Turn over 2 Use of the Data Booklet is relevant to this question. A vanadium salt of unknown oxidation state was dissolved in water to form a solution of 0.500 mol dm –3. It was found that 20.4 cm 3 of this solution will react with 1 .00 g of zinc powder to form vanadium(II) solution. What is the possible identity of the vanadium salt used? A V2+ B V3+ C VO2+ D VO2+ Answer: D Let the vanadium salt of unknown oxidation state be