2025 JC2 Prelims H2 Chem Paper 3 QP TJC

9729 / TJC Prelims / 2025 DO NOT WRITE IN THIS MARGIN [Turn over TEMASEK JUNIOR COLLEGE 2025 JC2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CENTRE NUMBER S INDEX NUMBER Chemistry 9729/03 Paper 3 Free Response Questions 15 September 2025 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, civics class, centre number and index number 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 questions. Section B Answer one question. A Data Booklet is provided. 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 27 printed pages and 1 blank page. For Examiner’s Use Paper 3 Q1 Q2 Q3 Q4 Q5 Total /80

2 DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2025 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN Section A Answer all the questions in this section. 1 Schweizer's reagent is used in purifying cellulose . This dark blue compound has the formula, [Cu(NH3)4(H2O)2](OH)2 and contains the tetraamminediaquacopper(II) cation, [Cu(NH3)4(H2O)2]2+. (a) Explain the origin of the dark blue colour of the tetraamminediaquacopper(II) cation. [3] ................................ ................................ ................................ ................................ ............. ................................ ................................ ................................ ................................ ............. ................................ ................................ ................................ ................................ ............. ................................ ................................ ................................ ................................ ............. ................................ ................................ ................................ ................................ ............. ................................ ................................ ................................ ................................ ............. ................................ ................................ ................................ ................................ ............. ................................ ................................ ................................ ................................ ............. ................................ ................................ ................................ ................................ ............. ................................ ................................ ................................ ................................ ............. ................................ ................................ ................................ ................................ ............. (b) When a solution of [Cu(NH3)4(H2O)2]2+ was gently heated, NH3 gas wa s released. A precipitate of Cu(OH)2 and NH4+ ions were also obtained as products. The Cu(OH)2 formed was purified and separated into two samples. One of the samples was added to concentrated hydrochloric acid, forming complex ion X. The other sample of Cu(OH)2 was added to dilute sulfuric acid, forming blue complex ion Y. [Cu(NH3)4(H2O)2]2+, X and Y are of different colours. When [Cu(NH3)4(H2O)2]2+ was strongly heated, a black solid Z is formed. (i) Write an equation for the reaction when a solution of [Cu(NH3)4(H2O)2]2+ was gently heated. [1] (ii) Write an equation for the reaction of Cu(OH) 2 with concentrated hydrochloric acid, forming X. [1] (iii) Suggest the identities of Y and Z. [2] (iv) Explain why [Cu(NH3)4(H2O)2]2+ and X are of different colours. [1] ................................ ................................ ................................ ................................ ... ................................ ................................ ................................ ................................ ...

3 DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelims / 2025 DO NOT WRITE IN THIS MARGIN [Turn over ................................ ................................ ................................ ................................ ... ................................ ................................ ................................ ................................ ... ................................ ................................ ................................ ................................ ... ................................ ................................ ................................ ................................ ... ................................ ................................ ................................ ................................ ... ................................ ................................ ................................ ................................ ... ................................ ................................ ................................ ................................ ... ................................ ................................ ................................ ................................ ... ................................ ................................ ................................ ................................ ... ................................ ................................ ................................ ................................ ... ................................ ................................ ................................ ................................ ... ................................ ................................ ................................ ................................ ... ................................ ................................ ................................ ................................ ... (c) Tetraamminediaquacopper(II) cation, [Cu(NH3)4(H2O)2]2+, has two possible stereoisomers. Draw the two stereoisomers. [2] ................................ ................................ ................................ ................................ .............. ................................ ................................ ................................ ................................ .............. ................................ ................................ ................................ ................................ .............. ................................ ................................ ................................ ................................ .............. ................................ ....