2021 EJC Prelim H3 Chemistry Paper 1 Suggested Solution and insert

© EJC [Turn Over EUNOIA JUNIOR COLLEGE JC2 Preliminary Examination 2021 General Certificate of Education Advanced Level Higher 3 CANDIDATE NAME CIVICS GROUP 2 0 – INDEX NUMBER CHEMISTRY Paper 1 9813/01 23 September 2021 2 hours 30 minutes Candidates answer on Question Paper. Additional Materials: Data Booklet Insert READ THESE INSTRUCTIONS FIRST Write your name, civics group and registration number on all the work you hand in. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staplers, 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 two questions. The use of an approved scientific calculator is expected, where appropriate. A Data Booklet is provided. 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. For Examiner’s Use Section A 1 / 20 2 / 11 3 / 10 4 / 19 Section B 5 / 20 6 / 20 7 / 20 Total / 100 This document consists of 35 printed pages and 1 blank page.

2 © EJC 9813/01/J2PE/21 Section A Answer all the questions in this section. 1 The information provided in the insert is taken from several published scientific articles. Other published articles may not agree with all of this information. You should read the whole insert before you start to answer any questions and use the information it contains to answer the questions. (a) (i) Write an equation for the main reaction in the carbonator, including state symbols. [1] (ii) Suggest a likely source for the calcium carbonate input. [1] (iii) Besides CO2, suggest the identity of two other gases which are likely to be the main constituent of flue gases. [1] (iv) With reference to your answer to (a)(iii) , s uggest the principle component of Gas Y exiting from the carbonator. [1] ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (i) CaO(s) + CO2(g) → CaCO3(s) (ii) One likely source for CaCO3 is limestone / chalk / dolomite. (iii) N2 and H2O(g) (iv) N2

3 © EJC 9813/01/J2PE/21 [Turn Over (b) One of the impurities in flue gases is sulfur dioxide from the combustion of sulfur - containing fuels. This can react in the carbonator to form calcium sulfate, which can accumulate over successive cycles and reduce the efficiency of the process. (i) Write an equation for the reaction of sulfur dioxide with calcium carbonate and oxygen to give two products, of which one is calcium sulfate. [1] (ii) By comparing the thermal stability of calcium sulfate and calcium carbonate, explain why calcium sulfate accumulates over successive cycles. [3] (iii) Name another impurity in flue gases and explain how this impurity comes about. [2] ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... (i) 2CaCO3 + 2SO2 + O2 → 2CaSO4 + 2CO2 (ii) CaSO4 accumulates over successive cycles as it is more thermally stable than CaCO3 at the temperatures used and is not decomposed to CaO in the calciner. Despite the sulfate anion being bigger than the carbonate anion, however, the sulfate anion being tetrahedral in shape is more spherical and have a larger surface area to volume ratio compared to the planar carbonate anion. Hence the sulfate anion is less polarisable than the carbonate anion, so the S–O bonds are weakened to a lesser extent than the C–O bonds, making calcium sulfate more thermally stable than calcium carbonate. (iii) Nitrogen oxides, NOx Reaction between N 2 and O 2 in air under the high temperature in the combustor.

4 © EJC 9813/01/J2PE/21 (c) Direct air capture (DAC) is a process which takes carbon dioxide directly