2024 Prelims SAJC H2 Chem P3 (Ans)

1 [TURN OVER ST ANDREW’S JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATIONS HIGHER 2 CANDIDATE NAME CLASS 2 3 S CHEMISTRY Paper 3 Free Response Candidates answer on the Question Paper. Additional Materials: Data Booklet 9729/03 9 September 2024 2 hours READ THESE INSTRUCTIONS FIRST Write your name and class on all the work that you hand in. Write in dark blue or black pen. You may use a HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Answer all questions in the spaces provided on the Question Paper. If additional space is required, you should use the pages at the end of this booklet. The question number must be clearly shown. Section A Answer all questions. Section B Answer one question. A Data Booklet is provided. The use of an approved scientific calculator is expected, where appropriate. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. This document consists of 32 printed pages (including this cover page). For Examiner’s Use Q1 8 Q2 21 Q3 20 Q4 11 Q5 or Q6 20 Total 80

2 [TURN OVER Section A Answer all the questions in this section. 1 (a) (i) Define the term relative atomic mass. [1] Relative atomic mass of an element is the average mass of 1 atom of the element relative to 1/12th the mass of 1 atom of 12C. [1] OR average mass of one atom of an element 1 12 the mass of one atom of carbon-12 [1] OR It refers to mass of one mole of atoms relative/compared to 1/12 (the mass) of 1 mole of 12C or in which 1 mole 12C (atom) has a mass of (exactly) 12g. (ii) Diamond, which is made up of both 12C and 13C atoms, has a relative atomic mass of 12.011. With reference to Table 1.1, calculate the percentage abundance of 13C in diamond. Table 1.1 Relative isotopic mass 12C 12.000 13C 13.003 [1] Let the percentage abundance of 13C be y%. (13.003)(y) + (12.000)(100-y) 100 =12.011 y = 1.096 ≈ 1.10 [1] (b) (i) Define the term enthalpy change of atomisation of C(graphite). [1] It refers to t he enthalpy change/energy required to form one mole of gaseous C atoms from C(graphite). [1] (ii) Some enthalpy change values are shown in Table 1.2. Table 1.2 value / kJ mol–1 enthalpy change of atomisation of C(diamond) +717

3 [TURN OVER enthalpy change of combustion of C(diamond) –395 enthalpy change of combustion of C(graphite) –393 Using the data in Table 1.2, construct a suitable energy cycle to show that the enthalpy change of atomisation of C(graphite) is +719 kJ mol–1. [3] [2] Hatom = -393 + 395 + 717 = +719 kJ mol–1 [1] (iii) Even though graphite and diamond are allotropes of carbon, they have different enthalpy change of atomisation. With reference to hybridisation of the car