EJC Prelim H1 Chemistry Paper 1 Worked Solutions

© EJC [Turn Over EUNOIA JUNIOR COLLEGE JC2 Preliminary Examination 2025 General Certificate of Education Advanced Level Higher 1 CHEMISTRY Paper 1 Multiple Choice 8873/01 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 12 printed pages.

2 © EJC 8873/01/J2PE/20 1 In which pair of atoms, in their ground states, have the same number of unpaired electrons? A B and Ca B F and Na C Ne and P D Be and Si Answer: B B: 1s22s22p1 (1 unpaired electrons in 2p subshell) Ca: 1s22s22p63s23p63d104s2 (No unpaired electrons) ✓ F: 1s22s22p5 (1 unpaired electrons in 2p subshell) ✓ Na: 1s22s22p63s1 (1 unpaired electrons in 3s subshell) Ne: 1s22s22p6 (No unpaired electrons) P: 1s22s22p63s23p3 (3 unpaired electrons in 3p subshell) Be: 1s22s2 (No unpaired electrons) Si: 1s22s22p63s23p2 (2 unpaired electrons in 3p subshell) 2 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. + – X Y Z

3 © EJC 9729/01/J2PE/25 [Turn over 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 . 3 Which molecule has the largest bond angle? A BF3 B SiCl4 C H2S D PH3 Answer: A A: BF3 has a trigonal planar shape, 3 bond pairs, 0 lone pair; F‒B‒F angle = 120° (largest) B: SiCl4 has a tetrahedral shape, 4 bond pairs, 0 lone pair; Cl‒Si‒Cl angle = 109.5° C: H2S has a bent shape, 2 bond pairs, 2 lone pairs; H‒S‒H angle = 104.5°