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 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

5 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 as shown below: A +1 7 = +0.14 B +3 11= +0.27 C −1 19 = –0.053 D −3 31= –0.10 5 Use of the Data Booklet is relevant to this question. The table shows the fifth, sixth, seventh, eighth and ninth ionisation energies ( IE) of an element in the third period. Element 5th 6th 7th 8th 9th IE/ kJmol–1 13352 16611 20115 25491 28934 What element has these ionisation energy values? A P B S C Cl D Ar Ans: C There is a sharp increase from the 7th to 8th IE. Hence, the 8th electron is taken from the inner shell, that is closer to the nucelus, hence, having a stronger attraction with the nucleus and more energy is required to remove. – Beam of ionic species +

6 6 Which molecules are not polar? 1 H2S 2 CS2 3 SO2 4 SF6 A 1 and 2 B 2 and 4 C 3 and 4 D 4 only Ans: B A: Bent/ polar (2 LP, 2 BP) B: Linear/ non-polar (0 LP, 2 BP) C: Bent/ polar (1 LP, 2 BP) D: Octahedral/ non-polar (0 LP, 6 BP) 7 The diagram shows the structure of part of a crystal of ice. Which statement is correct? A The hydrogen bonds, shown by the dotted lines, are stronger than the O −H covalent bonds. B The weaker covalent bonds in ice causes it to be less dense than water. C All the bond angles surrounding each oxygen atom are 120. D Each oxygen can form 2 hydrogen bonds. Ans: D Option A: The hydrogen bonds are weaker than the O−H covalent bonds. Option B: The open structure (due to hydrogen bonds) of ice causes ice to be less dense than water. Option C: All the bond angles surrounding each oxygen atom are 109.5. Option D:2 hydrogen bond per water molecule. Each hydrogen bond is formed from the interaction of a ɗ+H atom and a lone pair of electrons on O.

7 8 Some information about some of the elements of Period 5 of the Periodic Table is shown: element Rb Sr In Sn Sb Te I Xe Electrical conductivity high high high high high semi-conductor zero zero Boiling point / K 961 1650 2300 2540 1650 1260 457 165 Which statement about these elements is correct? A Both I and Xe have simple molecular structures. B Elements from Rb to Te have giant metallic structures. C There are less elements with metallic structures in Period 5 than in Period 3. D Sr has higher boiling point than Rb because of higher charge density. Ans: D Option A: Xe occurs is monoatomic as it is from Group 18 (noble gas - valence shell is complete) but I exists as I2 molecules. Option B: Te is a semi -conductor and in Group 16 - likely to have covalent structure. Option C: Rb→Sb are likely to have metallic structure as they have high electrical conductivity and boiling point. Hence there are more metals in Period 5 than Period 3 Option D: Bp of Rb (Group 1 metal) is lower because of its smaller charge and ionic radius (lower charge density) than Rb. It also implies that there is less electron delocalised, leading weaker metallic bonds than Sr.

8 9 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 IMF, 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)CH 3 Hydrogen Bonding U 72 (CH3)4C Id-id (weaker) V 72 CH3CH2CH2CH2CH 3 Id-id (stronger) 10 In a chlorine molecule, C l2, the two chlorine atoms are held together by a single covalent bond. The bond energy is 244 kJ mol–1. The bond length is 0.198 nm. What do the terms bond energy and bond length mean? bond energy bond length A the energy needed to make one mole of bonds the distance between the outer shells of the two bonded atoms B the energy needed to make one mole of bonds the distance between the nuclei of the two bonded atoms C the energy needed to break one mole of bonds the distance between the outer shells of the two bonded atoms D the energy needed to break one mole of