2025 SAJC H2 Chem Prelim P1 Answers

1 [Turn Over . ST. ANDREW’S JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATIONS HIGHER 2 CANDIDATE NAME CLASS 2 4 S CHEMISTRY Paper 1 Multiple Choice Candidate answer on the Optical Answer Sheet. Additional Materials: Data Booklet 9729/01 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 XX printed pages (including this cover page).

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

3 [Turn Over 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 carbon-12. 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 nitrogen is given by the following expression. average mass of one atom of nitrogen 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 cm3 of a gaseous hydrocarbon, CxHy, 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 were 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

4 [Turn Over Volume of reacted O2 =80 cm3 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 Charge Nucleon number A 3 +3 12 9 –3 12 B 8 0 16 11 –1 19 C 10 +1 23 10 +1 24 D 18 –3 31 12 +3 31 Ans: C Isotopes are elements with the same number of protons but different number of neutrons. X Y Conclusion protons neutrons protons neutrons A 6 6 6 6 Same element and isotope B 8 8 10 9 Different element C 11 12 11 13 Same element, different isotope D 15 16 15 16 Same element and isotope Commented [SXF(1]: Need table outline

5 [Turn Over 4 Which particle will deflect the most when moving with the same speed through an electric field? A Li7 + B B11 3+ C F19 − D P31 3− Ans: B Angle of deflection is dependent on charge/mass ratio. The charge/mass of the species are shown below: A +1 7 = +0.14 B +3 11 = +0.28 C −1 19 = – 0.05 D −3 31 = –0.10 5 Which molecules are not polar? 1 H 2 S 2 CS2 3 SO2 4 SF6 A 1 and 2 B 2 and 4 C 3 and 4 D 4 only Ans: B 1: Bent/ polar (2 LP, 2 BP) 2: Linear/ non-polar (0 LP, 2 BP) 3: Bent/ polar (1 LP, 2 BP) 4: Octahedral/ non-polar (0 LP, 6 BP) – Beam of ionic species +

6 [Turn Over 6 A mixture consisting of gaseous compounds, S, T, U and V, is slowly cooled. Gaseous Compound Mr Compound S 72 CH3CH2COCH3 T 74 CH3CH2CH(OH)CH3 U 72 (CH3)4C V 72 CH3CH2CH2CH2CH3 In which order, from first to last, will the compounds condense to form their liquids? A T → S → V → U B U → V → S → T C S → T → V → U D V → U → S → T Ans: A The stronger the intermolecular forces of attraction , the first the compound will condense, given Mr is similar. Hydrogen bonding> pd-pd> id-id of straight-chained molecule> id-id of branched Gaseous Compound Mr Compound Intermolecular forces of attraction S 72 CH3CH2COCH3 Pd-pd T 74 CH3CH2CH(OH)CH3 Hydrogen Bonding U 72 (CH3)4C Id-id (weaker) V 72 CH3CH2CH2CH2CH3 Id-id (stronger) 7 Which equation corresponds to the enthalpy change stated? A S8(s) + 12O2(g) → 8SO3(l) ∆HӨformation (SO3(l)) B CaCl2(s) + aq → Ca2+ (g) + 2Cl–(g) ∆HӨsolution (CaCl2(s)) C 2Fe3+(g) + 3O2–(g) → Fe2O3(s) HӨlattice energy (Fe2O3(s)) D H2SO4(aq) + Ca(OH)2(aq) → CaSO4(aq) + 2H2O(l) ∆HӨneutralisation Ans: C A: 8 X ∆HӨformation (SO3(l)) B: CaCl2(s) + aq → Ca2+ (aq) + 2Cl– (aq) C: 1 X HӨlattice energy (Fe2O3(s)) D: 2 X ∆HӨneutralisation Commented [SXF(2]: I added comma Commented [SXF(3]: Which equation corresponds to Commented [SXF(4]: Aligment

7 [Turn Over 8 Use of the Data Booklet is relevant to this question. A student mixes 20.0 cm 3 of 5.00 mol dm –3 sulfuric acid with an equal volume of 6.00 mol dm –3 sodium hydroxide. The initial temperature of both solutions is 25.0 °C. The maximum temperature reached after the reaction is 55.0 °C. Assume the density of both solutions is 1 g cm–3. What is the value of the enthalpy change of neutralisation, in kJ mol−1, calculated using these values? A –41.8 B –50.2 C –83.6 D –100.3 Ans: A Q = mc∆T = (40)(4.18)(30) = 5016 J No. of moles of H2SO4 = 20/1000 x 5 = 0.1 mol No of moles of H+ = 0.2 mol No. of moles of NaOH = 20/1000 x 6 = 0.12 mol The limiting agent is NaOH. No. of moles of H2O = 0.12 mol ∆H = – (5016) / 0.12 = –41800 J mol–1 = –41.8 kJ mol–1 9 The half-life of the first-order gaseous reaction in which M2 molecules become converted into M atoms is 40 minutes. 1 mol of M2 is put into a sealed vessel at pressure p. What will be true when 87.5% of M2 has been converted into M atoms? 1 80 minutes have elapsed. 2 1.5 mol of M have been formed. 3 The total pressure is 15 8 p (at constant pressure). A 1, 2 and 3 B 1 and 2 only C 2 and 3 only D 3 only Ans: D 1 120 minutes have elapsed as three half-lives have passed (12.5% of M2 remains is equivalent to 1/8 = (1/2)3) 2 After the first half-life, 0.5 mol of M2 will produce 1 mol of M. Commented [SXF(5]: Neutralisation and I included the units cos the A level qns has the units in the opions

8 [Turn Over After the second half-life, 0.25 mol of M2 will produce 0.5 mol of M. After the third half -life, 0.125 mol of M 2 will produce 0.25 mol of M. Total no. of moles of M = 1 + 0.5 + 0.25 = 1.75 mol 3 True. The initial pressure is p, containing only M 2. The change in the p is – 0.875p for M2 while +1.75p for M. Hence, The final pressure is 0.125p + 1.75p = 1.875 p. 10 Curves 1 and 2 show the Boltzmann distributions for identical compositions of a reaction mixture which occur at different temperatures. Which statement is correct? A Curve 1 applies to the faster reaction and point W indicates particles with lower energy than point Z. B Curve 1 applies to the faster reaction and point W indicates particles with higher energy than point Z. C Curve 2 applies to the faster reaction and point X indicates particles with lower energy than point Y. D Curve 2 applies to the faster reaction and point X ind