2024 Prelims YIJC H2 Chem P2 (Ans)

©YIJC [Turn over YISHUN INNOVA JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME SUGGESTED ANSWERS CG INDEX NO CHEMISTRY Paper 2 Structured Questions Candidates answer on the Question Paper. Additional Materials: Data Booklet 9729/02 10 September 2024 2 hours READ THESE INSTRUCTIONS FIRST This document consists of 17 printed pages and 3 blank pages. For Examiner’s Use 1 / 9 2 / 9 3 / 16 4 / 21 5 / 20 Penalty units significant figures Overall / 75 Write your name and class in the spaces at the top of this page. 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. The use of an approved scientific calculator is expected, where appropriate. A Data Booklet is provided. The number of marks is given in brackets [ ] at the end of each question or part question.

©YIJC [Turn over 2 Answer all the questions in the spaces provided. 1 (a) Calcium carbide, CaC2 is a solid used in the production of ethyne, C2H2. Calcium carbide is produced when calcium oxide reacts with carbon forming calcium carbide and carbon monoxide. (i) Write the electronic configuration of calcium in calcium carbide. Ca2+: 1s2 2s2 2p6 3s2 3p6 (ii) Write an equation, with state symbols for the formation of calcium carbide. CaO(s) + 3C(s) → CaC2(s) + 3CO(g) (iii) Predict all possible intermolecular forces which could exist between carbon monoxide molecules. Explain how these forces arise. Carbon monoxide has a simple molecular struct ure, with instantaneous dipole -induced dipole interactions and permanent dipole-permanent dipole interactions between the molecules. As electrons in orbitals are in constant random motion, there is an uneven distribution of electrons in a molecule/ distortion of the electron cloud. This separation of charges creates an instantaneous dipole in the molecule. Instantaneous dipole induce neighbouring molecules to undergo electron cloud distortion/ induce the formation of dipoles in the neighbouring molecule s and hence instantaneous dipole – induced dipole attraction occurs. Carbon monoxide being polar/ has net dipole moment/ has permanent net separation of charges due to difference in electronegativity between C and O atoms . Hence, permanent dipole-permanent dipole attraction occurs.

©YIJC [Turn over 3 (b) The German chemist Friedrich Wohler discovered that calcium carbide, CaC 2 reacted with water releasing ethyne gas, C2H2 and calcium hydroxide. The ethyne gas was burnt in miner’s lamps and headlig