EJC Prelim P4_Answer

© EJC 9729/04/J2PE/18 [Turn Over EUNOIA JUNIOR COLLEGE JC2 Preliminary Examination 2018 General Certificate of Education Advanced Level Higher 2 CANDIDATE NAME CIVICS GROUP 1 7 – INDEX NUMBER CHEMISTRY Paper 4 Practical 9729/04 28 August 2018 2 hours 30 minutes Candidates answer on the Question Paper. Additional Materials: As listed in the Confidental Instructions READ THESE INSTRUCTIONS FIRST Write your name, civics group and registration number on the work you hand in. Give details of the practical shift and laboratory, where appropriate, in the boxes provided. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use paper clips, highlighters, glue or correction fluid. Answer all questions in the spaces provided on the Question paper. The use of an approved scientific calculator is expected, where appropriate. You may lose marks if you do not show your working or if you do not use appropriate units. Qualitative Analysis Notes are printed on pages 19 and 20. 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. Shift Laboratory For Examiner’s Use 1 2 3 4 Total This document consists of 19 printed pages and 1 blank page.

2 © EJC 9729/04/J2PE/18 For Examiner’s Use Answer all the questions in the spaces provided. 1 Analysis of a solution containing both sodium hydroxide and sodium carbonate by Warder titration (double indicator method) Aqueous sodium hydroxide easily reacts with atmospheric carbon dioxide. This results in the sodium hydroxide being contaminated with sodium carbonate Na2CO3. The Warder titration (double indicator method) can be used to analyse a mixture containing both sodium hydroxide and sodium carbonate. FA 1 is 0.125 mol dm –3 hydrochloric acid, HCl. FA 2 is an aqueous solution containing sodium hydroxide, NaOH, and sodium carbonate, Na2CO3. (a) Titration of FA 2 against FA 1 using methyl orange or screened methyl orange indicator In this titration, FA 1 is run from the burette into the conical flask containing FA 2 with methyl orange or screened methyl orange indicator. The end-point is reached when the yellow colour changes to orange for methyl orange, or the green colour changes to grey for screened methyl orange. (i) 1. Fill the burette with FA 1. 2. Using a pipette, transfer 25.0 cm 3 of FA 2 into a conical flask. 3. Add a few drops of methyl orange or screened methyl orange indicator. 4. Run FA 1 from the burette into the conical flask until the colour of the solution changes. 5. Record your titration results in the space provided below. Make certain that your recorded results show the precision of your working. 6. Repeat points 1 to 5 as necessary until consistent results are obtained. Results [5]