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 ( ) [5] Summary Tick () the best titration results. Using these results, the average volume of Q required was ………….. cm3. Volume of solution P used was …………… cm3. [2]

4 (c) P contains 6.00 g of the impure sodium carbonate in 1.00 dm3. Q is 0.100 mol/dm3 hydrochloric acid. Using your results from (b), calculate the concentration, in mol/dm 3, of the sodium carbonate in P. Na2CO3 + 2HCl  2NaCl + H2O + CO2 concentration of sodium carbonate in P ……………….………… mol/dm3. [2] (d) Using your answer from (c), calculate the mass of sodium carbonate present in 1.00 dm3 of solution P. [the Mr of sodium carbonate is 106] mass of sodium carbonate present in 1.00 dm3 of solution P is ………….g [1] (e) Using your answer from (d), calculate the percentage by mass of sodium carbonate in the impure sample. percentage by mass of sodium carbonate in the impure sample is ………...….% [1]

5 (f) A student performed the above titration experiment. Before he started his titration, he washed the conical flask with solution P. He then added 25.0 cm 3 of solution P from the pipette. Describe and explain how this would affect the calculated concentration of solution P in part (c). ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… …..………………………………………………………………………………………….[3] [Total : 25] 2 The percentage purity of Na 2CO3 can be determined by titration as described in question 1. Na2CO3 + 2HCl  2NaCl + H2O + CO2 Based on the equation above, suggest another way to determine the percentage purity of sodium carbonate in the impure sample. ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… …………………………………………………………………………………………………

6 ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… …..………………………………………………………………………………………….[5]

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8 Preparation List (per student) Preparation List for Question 1: Apparatus Quantity (per student) Test Tube Rack with 4 test tubes 1 Test tube holder 1 Wooden splints (in goody bag) 2 Delivery tube 1 Bunsen burner 1 Glass rod 1 Chemicals/Materials Quantity (per student) Common bench reagent rack with: (a) Aqueous sodium hydroxide (1 mol/dm3) (b) Aqueous ammonia (1 mol/dm3) (c) Dilute hydrochloric acid (1 mol/dm3) (d) Dilute sulfuric acid (1 mol/dm3) (e) Dilute nitric acid (1 mol/dm3) (f) Limewater (g) Aqueous potassium iodide (0.5 mol/dm3) (h) Aqueous barium nitrate (0.2 mol/dm3) (i) Aqueous silver nitrate (0.05 mol/dm3) (j) Aqueous potassium manganate(VII) Shared per pair (Placed centrally between two candidates) Question 2 Chemicals [H] P 150 cm3 0.1 mol/dm3 hydrochloric acid [H] Q 200 cm3 6.00g of sodium carbonate in dm3 and sodium chloride as impurity Apparatus Burette (0 – 50.0 cm3) x 1 Filter Funnel x 1 Pipette (25 cm3) x 1 Retort stand and clamps x 1 250 cm3 conical flask x 2 Pipette filler x 1 Distilled water bottle x 1 White Tile x 1 Methyl orange Indicator x 1