SJI_2020 Year 3 EOY Chemistry 6092 P3

ST JOSEPH’S INSTITUTION END-OF-YEAR EXAMINATION 2020 (YEAR 3) CANDIDATE NAME CLASS INDEX NUMBER CHEMISTRY Paper 3 Practical Additional Materials : Nil 6092 / 03 16 September 2020 1 hour 15 min READ THESE INSTRUCTIONS FIRST Write your name, class and index number on the cover page of this Question Paper. Write in dark blue or black ink pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Answer all questions in the spaces provided. Candidates are reminded that all quantitative answers should include appropriate units. Candidates are advised to show all their working in a clear and orderly manner. The number of marks is given in brackets [ ] at the end of each question or part question. The use of an approved scientific calculator is expected, where appropriate. Qualitative Analysis Notes are printed on page 6. Shift Laboratory For Examiner’s Use Total / 30m This document consists of 7 printed pages including this cover page. [Turn Over

2 Question 1: P is a solution containing an impure sample of sodium carbonate. The impurity is a sodium compound. You are to identify the impurity and then determine, by titration with hydrochloric acid, the amount of sodium carbonate present in the impure sample. P contains 6.00 g of the impure sodium carbonate in 1.00 dm3. Q is 0.100 mol/dm3 hydrochloric acid. (a) Identification of the impurity in P. Carry out the following tests on solution P and record your observations in the table. Test and identify any gas evolved. test no. test observations 1 (a) To a portion of P, add an equal volume of aqueous barium nitrate. 1 (b) Add dilute nitric acid to the mixture from 1(a). 2(a) To a portion of P, add a few drops of aqueous silver nitrate. 2(b) Add dilute nitric acid to the mixture from 2(a). [8]

3 The formula of the impurity present in P is ………………………………. [1] (i) Write the ionic equation , with state symbols, for the formation of the compound in 2(a) that leads to the identification of the unknown anion. …..………………………………………………………………………………...[2] (b) Determination of the concentration of the sodium carbonate in P. Put Q into the burette. Pipette a 25.0 cm3 portion of P into a flask and titrate with Q, using the indicator provided. Record your results in the table below, repeating the titration as many times as you consider necessary to achieve consistent results. Results: Titration number Final burette reading / cm3 Initial burette reading / cm3 Volume of Q used / cm3 Best titration results ( )