2022 YIJC H2 CHEM PRELIM P3 MS

©YIJC [Turn over YISHUN INNOVA JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME SUGGESTED ANSWERS CG INDEX NO CHEMISTRY Paper 3 Free Response Candidates answer on the Question Paper. Additional Materials: Data Booklet 9729/03 12 September 2022 2 hours READ THESE INSTRUCTIONS FIRST This document consists of 26 printed pages and 6 blank pages For Examiner’s Use Section A 1 / 17 2 / 18 3 / 25 Section B 4 or 5 / 20 Penalty units significant figures Overall / 80 Write your name, class and index number on all the work you hand in. Write in dark blue or black pen on both sides of the paper. 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 scientific 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.

2 ©YIJC [Turn over Section A Answer all the questions in this section. 1 (a) Describe and explain the trend in the thermal stability of the hydrogen halides, HCl, HBr and HI. Include an equation for the thermal decomposition reaction in your answer. [3] HX(g) → ½H2(g) + ½X2(g) The thermal stabilities of the hydrogen halides decrease down the Group from HCl to HBr to HI. This is because • the size of the halogens increases from Cl to I and the valence orbital used for bonding is larger and more diffuse; • the effectiveness of the orbitals overlap decreases; • this result in the weaker covalent bond formed between the hydrogen and halogen atoms or quoting H-X bond energies; • lesser amount of energy is required to overcome the covalent bond between the hydrogen and halogen atoms. (b) Alkanes are generally considered to be unreactive compounds, showing an inertness to common reagents such as NaOH, H2SO4, and K2Cr2O7. (i) Suggest a reason why these reagents do not react with an alkane such as propane. [1] The C-H bond is non-polar. The C-H bond does not break heterolytically, only homolytically. Propane can be converted into 2-chloropropane when it reacts with chlorine in ultraviolet