CJC Prelim P4_SOL

1 CANDIDATE NAME CLASS 2T CHEMISTRY 9729/04 Paper 4 Practical 16 August 2017 2 hour 30 minutes Candidates answer on the Question Paper. Additional Materials: As listed in the Confidential Instructions READ THESE INSTRUCTIONS FIRST Write your name and class in the boxes above. 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 staples, paper clips, 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 15 and 16. 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. This document consists of 15 printed pages and 1 blank page. [Turn over Instruction Catholic Junior College JC2 Preliminary Examinations Higher 2 Shift Laboratory For Examiner’s Use 1 2 3 Total Suggested Solutions

2 Answer all the questions in the spaces provided. 1 'Washing soda' is made from crystals of sodium carbonate, which contains 62.94 % water and 37.06 % sodium carbonate. When stored, these crystals lose some of the water in the crystals to the atmosphere. FA 1 is solid 'washing soda', originally sodium carbonate decahydrate, Na2CO3.10H2O. FA 2 is 0.100 mol dm–3 hydrochloric acid, HCl. In this question, you will perform a titration to determine the amount of water in FA 1 that has been lost to the atmosphere. (a) Method (i) Preparation of FA 3  Weigh the 100 cm3 beaker provided. Record the mass in the space below.  Tip the 'washing soda' crystals, FA 1, into the beaker. Weigh the beaker with FA 1 and record the mass.  Calculate the mass of FA 1 used and record this in the space below.  Add distilled water to the beaker to dissolve the crystals. Carefully transfer the solution to a 250 cm 3 graduated (volumetric) flask labelled FA 3. Wash the beaker twice with small quantities of water and add these washings to the volumetric flask.  Make the solution up to the mark using distilled water. Stopper the flask and invert a number of times to ensure thorough mixing. [1] (ii) Titration of FA 3 against FA 2  Fill the burette with FA 2.  Pipette 25.0 cm 3 of FA 3 into a conical flask and add a few drops of the indicator provided.  Titrate the solution with FA 2. Record your results in the space provided on page 3. Make certain that the recorded results show the precision of your practical work.  Repeat the titration until consistent results are obtained. mass of beaker + FA1 / g 21.138 mass of be