2023 SAJC H2 Chem Prelim P3 (Ans)

ST ANDREW’S JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATIONS HIGHER 2 CANDIDATE NAME CLASS 2 2 S CHEMISTRY Paper 3 Free Response Candidates answer on the Question Paper. Additional Materials: Data Booklet 9729/03 14 September 2023 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. The number of marks is given in brackets [ ] at the end of each question or part question. This document consists of XX printed pages (including this cover page). For Examiner’s Use Q1 21 Q2 20 Q3 19 Q4 or Q5 20 Total 80

Section A Answer all the questions in this section. 1 In the manufacture of tinted glass for chapels, a variety of carbonates including calcium carbonate were smelted together to form the needed colourations. (a) (i) Draw a ‘dot-and-cross’ diagram to show the bonding present within a carbonate ion, CO32−. [1] Accept x instead of • for the added e on the O (ii) State and explain, with reference to the VSEPR theory, the shape of the carbonate ion. [2] The carbonate ion has 3 bond pairs and 0 lone pairs around the central C. To minimise (electrostatic) repulsion (between the electron pairs , the shape of carbonate ion will be trigonal planar. (iii) When sodium carbonate was added to water, a weakly alkaline solution is produced. Write an equation for this reaction. [1] CO32-(aq) + H2O(l) ⇌ HCO3- (aq) + OH–(aq) (b) (i) Write a balanced equation, with state symbols, for the thermal decomposition of calcium carbonate under standard conditions. [1] CaCO3 (s) → CaO (s) + CO2(g) (ii) Construct a fully labelled energy cycle to show that the standard enthalpy change of formation of carbon dioxide is −399 kJ mol-1. Your cycle should include relevant data from the Data Booklet together with the following data. Standard enthalpy change of atomisation of carbon = +715 kJ mol−1 [2] C O O O x x xx xx xxxx xx xx xx x x 2-

[1] ΔHf = +715 + 496 – 805 x 2 = –399 kJ mol–1 (iii) The standard enthalpy changes of formation for these species are shown in the following table. Species CaCO3(s) CaO (s) CO2(g) ΔHfº / kJ mol–1 –1207 –635 –399 Using your answer in (b)(i) and (ii), calculate the standard enthalpy change of decomposition of calcium carbonate. [1] ΔHreaction = ΔHfo(CaO(s)) + ΔHfo(CO2(g)) –