2020 YIJC Prelim P4 QP

1 YIJC [Turn over YISHUN INNOVA JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION CANDIDATE NAME CLASS DATE H2 CHEMISTRY 9729/04 Paper 4 Practical Paper Thursday 25 August 2020 2 hours 30 minutes Candidates answer on question paper. No Additional Materials are required READ THESE INSTRUCTIONS FIRST This document consists of 18 printed pages and 2 blank pages. Write your name and class in the spaces at the top of this page. 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 18 and 19. 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 1 22 2 19 3 14 Total 55 Shift Laboratory

2 YIJC [Turn over Answer all the questions in the spaces provided. 1 To determine the relative atomic mass of an unknown Group 1 element and the concentration of sulfuric acid solution using a graphical method FA 1 is a solution of sulfuric acid FA 2 is 0.550 moldm3 sodium hydroxide, NaOH FA 3 is solution of unknown Group 1 carbonate, M2CO3 FA 4 is methyl orange indicator Both the Group 1 carbonate and sodium hydroxide are bases which will neutralise sulfuric acid. M2CO3 + H2SO4  M2SO4 + CO2 + H2O 2NaOH + H2SO4  Na2SO4 + 2H2O In this experiment, you will add different volumes of FA 3 to identical samples of dilute sulfuric acid, FA 1. In each case, the amount of the Group 1 carbonate solution you add will only partially neutralise the sulfuric acid. You will then complete the neutralisation of each mixture by titration with s odium hydroxide, FA 2. Each titration is to be performed once only, so great care should be taken that you do not overshoot the end-points. Graphical analysis of your results will enable you to determine the relative atomic mass of the Group 1 element, and the concentration of the sulfuric acid solution. (a) Preparation of titration mixtures Prepare four different mixtures of FA 1 and FA 3 as described below. Mixture 1 1. Pipette 25.0 cm3 of FA 1 into a conical flask. 2. Fill a burette with FA 3. 3. Add 6.00 cm3 of FA 3 into the same conical flask. 4. Thoroughly stir the mixture and set it aside for later use. Mixture 2 Repeat the procedure used for Mixture 1 but this time add 25.0 cm 3 of FA 1 and 20.00 cm3 of FA 3 into a second conical flask. Mixtures 3 and 4 Select two other suitable volumes of FA 3 for use in two additional experiments. Your selected volumes must be between the volumes used in Mixture 1 and 2. Repeat the procedures used for Mixture 1 but, in each case, add 25.0 cm 3 of FA 1 and your chosen volume of FA 3 into a 100 cm3 beaker. You may label the 100 cm3 beaker with the volume of FA 3 added using a pencil and the sticker label provided, but do remember to remove them after the experiment.

3 YIJC [Turn over (b) Titration Each titration is to be performed once only, so great care should be taken that you do not overshoot the end-points. 1. Fill the second burette with FA 2. 2. Add 4 drops of FA 4 to the conical flask containing Mixture 1. 3. Titrate the mixture in the conical flask with FA 2 until the solution changes from red to orange. 4. Repeat points 1 to 3 above using your remaining mixtures. Mixtures 3 and 4 stored in the 100 cm 3 beakers should be transferred completely to a conical flask prior to each titration. Rinse the conical flask thoroughly between each titration. 5. Record your titration results, to an appropriate level of precision, in the space provided. In addition, you need to record the volume of FA 3 added to each mixture in your table. Table of results [4]

4 YIJC [Turn over (c) Plot on the grid below, your values for the FA 2 titre (y-axis) against the volume of FA 3 added (x-axis). You should choose scales for the axes which allow you to determine by extrapolation  the volume of FA 3 required, Vmax(FA 3), to react completely with 25.0 cm 3 of FA 1 if no FA 2 is added;  the volume of FA 2 required, Vmax(FA 2), to react completely with 25.0 cm 3 of FA 1 if no FA 3 is added. Draw the line of best fit, taking into account all of your plotted points. Henc e obtain values for Vmax(FA 3) and Vmax(FA 2). Vmax(FA 3) = ………………………… Vmax(FA 2) = ………………………… [6]

5 YIJC [Turn over (d) Calculate the gradient of your graph line, showing clearly how you did this. gradient = ……………………. [1] (e) Explain in terms of the chemistry involved, the direction of the slope of your graph. ………………………………………………………………………………………………………….… ……………………………………………………………………………………………………………. [1] (f) (i) Using Vmax(FA 2) from your graph, calculate the concentration of sulfuric acid in FA 1. concentration of H2SO4 in FA 1 = ……………………. [2] (ii) Using your answer in (f)(i) and Vmax(FA 3) from your graph, calculate the concentration of the Group 1 carbonate in FA 3. concentration of M2CO3 in FA 3 = ……………………. [1]

6 YIJC [Turn over (iii) FA 3 contains 39.75 g dm3 of M2CO3 in deionised water. Using this information as well as your answer from (f)(ii), calculate the relative atomic mass of M. [Ar: C, 12.0; O, 16.0] relative atomic mass of M = ……………………. [1] (g) A student performs this experiment using a FA 2 solution that was left uncovered overnight in the laboratory. Suggest what effect this will have on the value of Vmax(FA 2) he obtains and explain your answer. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. [1] (h) Explain, in terms of the uncertainties associated with the apparatus used, why your FA 2 titre volume for mixture 1 is likely to be more accurate than that for mixture 2. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. ……………………………………………………………………………………………………………. [2]

7 YIJC [Turn over (i) Determining the basicity of an unknown acid X (i) FA 5 is a solution of 0.75 mol dm3 of an acid X. FA 6 is 1.50 mol dm3 sodium hydroxide, NaOH You will carry out two experiments to determine the basicity of acid X by mixing different volumes of FA 5 with FA 6 as stated in the table provided and measuring the maximum temperature reached. You may use the following apparatus to carry out the experiments:  2 × measuring cylinders  1 × thermometer  1 × styrofoam cup with cover  1 × glass beaker Record the initial temperature of the FA 5 solution and the maximum temperature reached in the table. Use your results to determine the maximum change in temperature for each experiment and complete the table. You may assume that the initial temperature of FA 6 is the same as that of FA 5. experiment volume of FA 5 /cm3 volume of FA 6 /cm3 initial temperature of FA 5 /oC maximum temperature / oC maximum change in temperature / oC 1 20.0 40.0 2 40.0 20.0 [1] (ii