EJC Prelim H2 Chemistry Paper 1 Worked Solution (updated)

© EJC [Turn Over EUNOIA JUNIOR COLLEGE JC2 Preliminary Examination 2025 General Certificate of Education Advanced Level Higher 2 CHEMISTRY Paper 1 Multiple Choice 9729/01 19 September 2025 1 hour Additional Materials: Multiple Choice Answer Sheet Data Booklet READ THESE INSTRUCTIONS FIRST Write in soft pencil. Do not use staples, paper clips, glue or correction fluid. Write your name, civics group and registration number on the Answer Sheet in the spaces provided unless this has been done for you. There are thirty questions on this paper. Answer all questions. For each question there are four possible answers A, B, C and D. Choose the one you consider correct and record your choice in soft pencil on the separate Answer Sheet. Read the instructions on the Answer Sheet very carefully. Each correct answer will score one mark. A mark will not be deducted for a wrong answer. Any rough working should be done in this question paper. The use of an approved scientific calculator is expected, where appropriate. This document consists of 13 printed pages and 3 blank pages.

2 © EJC 9729/01/J2PE/25 1 Three particles approach an electric field at the same speed. They are deflected as they pass through the electric field. What could be the identities of particles X, Y and Z? X Y Z A 35 17Cl– 37 17Cl– 23 11Na+ B 6 3Li+ 7 3Li+ 1 1H– C 37 17Cl– 35 17Cl– 23 11Na+ D 7 3Li+ 6 3Li+ 1 1H– Answer: A Since particles X and Y are deflected to the positive terminal, they are negatively charged. Since particle Z is deflected to the negative terminal, it is positively charged. Hence, X and Y must be Cl− while Z must be Na+ (either option A or C is correct). Between particles X and Y, the larger angle of deflection of particle X indicates that its 𝑒 𝑚 ratio is larger than that of Y. Hence, particle X should have a smaller mass number than particle Y since both X and Y have the same charge. Hence, X is Cl – 17 35 while Y is Cl – 17 37 . + – X Y Z

3 © EJC 9729/01/J2PE/25 [Turn over 2 Which of the following about calcium and copper is correct? A The outermost orbital of the atoms of both elements has the same shape. B Atom of both elements have orbitals of only 2 different shapes of various sizes. C Atom of both elements have the same number of electrons in the outermost shell. D Both elements form ions of 2+ charge with the electronic configuration of [Ar]. Answer: A Ca: 1s2 2s2 2p6 3s2 3p6 4s2 Cu: 1s2 2s2 2p6 3s2 3p6 3d10 4s1 Ca2+: 1s2 2s2 2p6 3s2 3p6 or [Ar] Cu2+: 1s2 2s2 2p6 3s2 3p6 3d9 or [Ar] 3d9 A ✓: Both atoms have 4s orbital as the outermost filled orbital. Thus, they have the same shape. B ×: Ca has s and p orbitals (2 different shapes), but Cu has s, p and d orbitals (3 different shapes). C ×: Ca has 2 electrons in the outmost shell (4s) while Cu has only 1 electron. D ×: Thus, the ions do not have the same electronic