SRJC_H1_CHEM_P1_ANS

1 Turn Over] SERANGOON JUNIOR COLLEGE General Certificate of Education Advanced Level Higher 1 Candidate Name Class CHEMISTRY 8872/01 JC2 Preliminary Examination 28 Aug 2015 Paper 1 Multiple Choice 50 min Additional Materials: Data Booklet Optical Mark Sheet (OMS) READ THESE INSTRUCTIONS FIRST On the separate multiple choice OMS given, write your name, subject title and class in the spaces provided. Shade correctly your FIN/NRIC number. There are 30 questions in this paper. Answer all questions. For each question there are four possible answers A, B, C and D. Choose the one you consider c orrect and record your choice using a soft pencil on the separate OMS. Each correct answer will score one mark. A mark will not be deducted for a wrong answer. You are advised to fill in the OMS as you go along; no additional time will be given for the transfer of answers once the examination has ended. Any rough working should be done in this question paper. This document consists of ___ printed pages and __ blank page.

2 Turn Over] Answer all questions 1 Oxides of nitrogen, NxOy, are air pollutants. In a reaction, 0.30 mol of NxOy is reacted with 30 dm 3 of hydrogen gas at room temperature and pressure and passed over a heated catalyst to produce ammonia and water as the only products . At the end of the reaction, 1.20 dm 3 of hydrogen gas remains . The ammonia produced required 0.300 mol of sulfuric acid for complete neutralisation. What is the molecular formula of the oxide? A NO B NO2 C N2O D N2O4 Answer: C NxOy + 2 )23( yx  H2  xNH3 + yH2O 0.30 mol 1.20 mol 0.600 mol No. of moles of H2 = (30-1.2)/24 = 1.20 2NH3 ≡ H2SO4 No. of moles of NH3 = 0.300 x 2 = 0.600 Comparing mole ratio, NxOy : NH3 1 : 2  x = 2 Comparing mole ratio, NxOy : H2 1 : 4 2 )23( yx  = 4  y = 1 Molecular formula is N2O. 2 In an experiment, H 2S was reacted with 28.00 cm 3 of 0.250 mol dm 3 of an unknown arsenate species, H 3AsOx, in a strongly acidic medium to form a yellow solid of mass 0.225 g and ortho–arsenite, AsO3 3. Determine the oxidation state of As in H3AsOx. A +2 B +3 C +4 D +5 Answer: D Unknown yellow solid is S (Deduction). H2S  S + 2H+ + 2e H3AsOx + ne AsO3 3 (unbalanced equation) +3 Mole ratio: 0.250 x 1000 28 H3AsOx ≡ 32.1 0.225 S 0.007 H3AsOx ≡ 0.007 S H3AsOx ≡ S  n = 2 Since final oxidation state of AsO3 3 = +3, initial oxidation state must be +5.

3 Turn Over] 3 The ion E2+ has 86 electrons and 138 neutrons. Which of the following statements is true? A Element E is isoelectronic with radon. B The first ionisati