ACJC H2 Chem 2021 Paper 3 (suggested solutions for exchange)

Index No. Name Form Class Tutorial Class 2CH________ Subject Tutor ANGLO-CHINESE JUNIOR COLLEGE DEPARTMENT OF CHEMISTRY Preliminary Examination CHEMISTRY H2 9729/03 Higher 2 Paper 3 Free Response 30 August 2021 Candidates answer on the Question Paper. 2 hours Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your index number and name, form class and tutorial class on all the work you hand in. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Answer all questions in the spaces provided on the Question Paper. If additional space is required, you should use the pages at the end of this booklet. The question number must be clearly shown. Section A Answer all the questions. Section B Answer one question. The use of an approved calculator is expected, where appropriate. A Data Booklet is provided. 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. Please fill in the question number for the question attempted. Section Question No. For Examiner’s Use Marks A 1 2 3 4 B Presentation of answers TOTAL: 80 m This document consists of 31 printed pages and 1 blank page. 9729/03/Prelim/21 ANGLO-CHINESE JUNIOR COLLEGE © ACJC 2021 Department of Chemistry [Turn over

2 © ACJC2021 9729/03/Prelim/2021 [Turn over Section A Answer all the questions in this section. 1 (a) Describe the reactions, if any, when separate samples of the oxides Na2O, Al2O3 and P4O10 are added to water. Write equations where appropriate and suggest the pH of any aqueous solution formed. [4] Na2O hydrolyses/dissolves / is soluble in water to give a colourless solution of NaOH with pH 13. Na2O(s) + H2O(l)  2NaOH(aq) Al2O3 is insoluble in water and hence pH remains at 7. P4O10 hydrolyses / dissolves / is soluble in water / reacts with water to give a colourless solution of H3PO4 with pH 2 (accept 1) P4O10(s) + 6H2O(l)  4H3PO4(aq) (b) Phosphorus pentachloride, PCl5, is a white, moisture-sensitive solid. It is a dangerous substance as it reacts violently with water. (i) PCl5 reacts completely with a large excess of water to form phosphoric acid, H3PO4. Write a balanced equati on for this reaction. State the approximate pH value of the resulting solution.