2025 SAJC H1 Chem Prelim P1_Answers

1 ST ANDREW’S JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATIONS HIGHER 1 WORKED SOLUTIONS CANDIDATE NAME CLASS 2 4 S CHEMISTRY Paper 1 Multiple Choice Candidate answer on the Optical Answer Sheet Additional Materials: Data Booklet 8873/01 18 September 2025 1 hour READ THESE INSTRUCTIONS FIRST Write in soft pencil. Do not use staples, paper clips, glue or correction fluid. 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 Optical Answer Sheet. 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 booklet. The use of an approved scientific calculator is expected, where appropriate. This document consists of 21 printed pages (including this cover page).

2 Answer 1 C 11 C 21 D 2 D 12 C 22 B 3 C 13 B 23 C 4 B 14 C 24 A 5 C 15 C 25 A 6 B 16 B 26 A 7 D 17 C 27 D 8 D 18 A 28 B 9 A 19 B 29 C 10 D 20 C 30 B

3 1 Which statement is correct? A One mole of a compound is the amount that contains the same number of atoms as there are in 12.0 g of C12 . B The relative isotopic mass of beryllium-9 is given by the following expression. average mass of all isotopes of beryllium 1 12 the mass of one atom of C12 C The relative atomic mass of oxygen is given by the following expression. average mass of one atom of oxygen 1 12 the mass of one atom of C12 D The relative molecular mass of Q is given by the following expression. average mass of one atom of Q 1 12 the mass of one atom of C12 Ans: C A: Incorrect. The number of moles of a compound is not the same as the number of moles of atoms in a compound. B: Incorrect. It should be “the mass of the isotope of Be” C: Correct as defined. D: Incorrect. It should be “average mass of one molecule of the substance” 2 10 cm 3 of a gaseous hydrocarbon, C xHy, was exploded with an excess of oxygen. There was a contraction of 40 cm3. When the product s were treated with aqueous sodium hydroxide, there was a further contraction of 50 cm3. All gas volumes are measured at room temperature and pressure. What is the molecular formula of the hydrocarbon? A C4H8 B C4H10 C C5H10 D C5H12 Ans: D Volume of CO2 = 50 cm3 Let the volume of reacted O2 be V cm3 10 + V = 40 + 50 Volume of reacted O2 =80 cm3

4 CxHy(g) + (x + 4 y ) O2(g) → x CO2(g) + 2 y H2O(l) 10 80 50 1 8 5 x = 5 5 + y/4 = 8 y = 12 Molecular formula of the hydrocarbon is C5H12 3 In which row are X and Y atoms or ions of different isotopes of the same element? X Y Number of electrons charge Nucleon number Number of electrons c