H1 Chemistry Prelim P2 Answers_ACJC

This document consists of 25 printed pages and 1 blank page. Anglo-Chinese Junior College JC2 Preliminary Examination Higher 1 CANDIDATE NAME FORM CLASS TUTORIAL CLASS 2CHX _ _ INDEX NUMBER CHEMISTRY Paper 2 Structured Questions Candidates answer on the Question Paper. Additional Materials: Data Booklet 8873/02 27 Aug 2025 2 hours READ THESE INSTRUCTIONS FIRST Write your name and index number in the spaces on all the work you hand in. Write in dark blue or black pen. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Section A Answer all questions. Section B Answer one question. The use of approved scientific calculator is expected, where appropriate. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiners’ use only Section A 1 / 13 2 / 7 3 / 10 4 / 7 5 / 13 6 / 10 Section B 7 or 8 / 20 Total / 80

2 ACJC 2025 8873/02/2025 Section A Answer all questions in this section in the spaces provided. 1 In the presence of an acid catalyst, ethanal reacts with methanol to form 1,1-dimethoxyethane. CH3CHO(l) + 2CH3OH(l) ⇌ CH3CH(OCH3)2(l) + H2O(l) ethanal methanol 1,1-dimethoxyethane (a) 0.20 mol dm−3 of ethanal and 0.1 mol dm−3 of methanol were placed in a reaction vessel. Strong acid was then added as a catalyst. It was found that the equilibrium mixture contained 0.025 mol dm−3 of 1,1-dimethoxyethane. Calculate the equilibrium concentrations of the other reactants and products. CH3CHO CH3OH 1,1- dimethoxyethane H2O Initial/ mol dm−3 0.20 0.10 0.00 0.00 Change/ mol dm−3 – 0.025 – 0.05 + 0.025 + 0.025 At equilibrium/ mol dm−3 0.175 0.05 0.025 0.025 [3] (b) Write the expression for the equilibrium constant for this reaction, Kc, stating its units. Kc = [CH3CH(OCH3)2] [H2O]/ [CH3CHO] [CH3OH]2 mol-1dm3 [2] (c) Use your answers in (a) to calculate the value of Kc. Kc = [0.025] [0.025]/ [0.175] [0.05]2 = 1.43 mol-1dm3 [1] H+

3 ACJC 2025 8873/02/2025 [Turn over (d) 2-methylpropenoic acid can be obtained from 2-methylprop-2-en-1-ol. (i) To prevent the C=C bond from reacting in other reactions, reaction 1 is first carried out. Draw the structure of A. [1] (ii) Suggest the reagents used in reaction 1. HBr(g) ……………