Copy of 2024 ANDSS 6092 Prelim P3 QP

This paper consists of 11 printed pages and 1 blank page. O ANDERSON SECONDARY SCHOOL Preliminary Examination 2024 Secondary Four Express CANDIDATE NAME: CLASS: / INDEX NUMBER: CHEMISTRY Paper 3 Practical 6092/03 16 August 2024 1 hour 50 minutes Candidates answer on the Question Paper Additional Materials: Nil READ THESE INSTRUCTIONS FIRST Write your name, class and index number on all 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 staples, paper clips, highlighters, glue or correction fluid/tape. 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 page 12. 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

PRELIM 4E CHEM 2024 6092/03 2 1 (a) Read all the instructions carefully before starting the experiments in Question 1. You are provided with salt solution W in a boiling tube. You will carry out tests on W to deduce its identity. You should test and identify any gases evolved. Record all your observations in the table. The volumes given below are approximate and should be estimated rather than measured, unless instructed otherwise. test observations Test 1 Put about 1 cm depth of solution W in a clean test-tube. Add 1 cm depth of aqueous sodium hydroxide. Gently warm the mixture. Test 2 Put about 1 cm depth of solution W in a clean test-tube. Add an equal depth of dilute nitric acid and then add a few drops of aqueous barium nitrate. Test 3 Put about 1 cm depth of solution W in a clean test-tube. Add an equal depth of dilute nitric acid and then add a few drops of aqueous silver nitrate. [4] (b) Deduce the identity of salt W. …………………………………………………………………………………… [2] [Total: 6]

PRELIM 4E CHEM 2024 6092/03 3 2 Malic acid is a carboxylic acid found in apple juice. The equation for the reaction between malic acid, H 2C4H4O5, and potassium hydroxide, KOH, is shown. 2KOH + H2C4H4O5 → K2C4H4O5 + 2H2O The concentration of aqueous malic acid is determined by titration with aqueous potassium hydroxide, KOH(aq). Thymolphthalein is used to determine the end-point of the titration. P is aqueous malic acid. Q is 0.100 mol/dm3 KOH(aq). (a) (i) Put P into the burette. Pipette 25.0 cm 3 of Q into a conical flask and titrate it with P using three drops of thymolphthalein as the indicator. The end-point is when the solution remains colourless permanently. Record your titration results in an appropriate format in the space provided. Repeat the titration as many times as necessary to achieve consistent results. Results [5]

PRELIM 4E CHEM 2024 6092/03 4 (ii) Use your titration results to obtain the average volume of P used. Show clearly how you obtained this volume. average volume of P = ……………………… [1] (b) Calculate the amount, in moles, of potassium hydroxide in 25.0 cm3 of Q. amount of potassium hydroxide = …………… mol [1] (c) Calculate, the amount, in moles, of malic acid present in the average volume of P. amount of malic acid = ………………. mol [1] (d) Use your answer to (c) to calculate the concentration of malic acid in P. concentration of malic acid in P = ………………. mol/dm3 [1]

PRELIM 4E CHEM 2024 6092/03 5 The average concentration of malic acid in apple juice is 4.50 g/dm3. (e) Calculate the average concentration of malic acid in apple juice in mol/dm3. [Ar: H,1; C,12; O,16] average concentration of malic acid = ……………… mol/dm3 [2] (f) Use your answers from (d) and (e) to calculate the average volume , in dm 3, of apple juice which contains the same mass of malic acid as 200 cm3 of P. average volume of apple juice = ………………. dm3 [2] (g) Suggest why accurate titration of apple juice with potassium hydroxide usually produces an average concentration higher than your answer from (e). ……………………………………………………………………………………. ……………………………………………………………………………………. [1] [Total: 14]

PRELIM 4E CHEM 2024 6092/03 6 3 Read through the entire procedure before you begin this question. You are to determine the enthalpy change for the reaction of a known volume and concentration of copper(II) sulfate and an excess of powdered zinc. The reaction is as follow: Cu2+(aq) + Zn(s) → Zn2+(aq) + Cu(s) R is 0.800 mol/dm3 copper(II) sulfate, CuSO4. T is powdered zinc, Zn. (a) • Remove the cap from the container with solid T. • Weigh the container with solid T. Record the mass. • Nest the polystyrene cup in a beaker. • Measure and transfer 30.0 cm3 of solution R into the polystyrene cup. • Place the thermometer into the solution. Measure and record the initial temperature of the solution in the table provided. This is the temperature at time zero minutes. • Start the stopwatch. Measure and record the temperature of the solution every half minute for 2 minutes. • At 2.5 minutes, add all the solid T into the solution and stir the mixture gently with the thermometer. • Measure and record the temperature of the mixture at 3 minutes and every half minute until 9 minutes. Stir the mixture between the thermometer readings. • Reweigh the container with any residual solid T. Record the mass. • Calculate and record the mass of solid T added to solution R. • Empty the content in the polystyrene cup into the container marked as “waste”. Do not pour the content into the sink. Results time / minutes 0 0.5 1 1.5 2 2.5 3 3.5 4 temperature / oC time / minutes 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 temperature / oC [3]

PRELIM 4E CHEM 2024 6092/03 7 (b) (i) Plot your results on the grid with temperature on the y-axis and time on the x-axis. Note that the scale for temperature should extend at least 10oC above your highest recorded temperature. Complete the graph by drawing two straight lines of best-fit through the points on your graph. The first line should be for the temperature before adding T and the second for the cooling of the mixture. Extend these two lines to 2.5 minutes. Draw a vertical line at 2.5 minutes to connect these lines. [4] (ii) Use your lines from (b)(i) to determine the theoretical rise i n temperature at 2.5 minutes. theoretical rise in temperature = ………….oC [1]

PRELIM 4E CHEM 2024 6092/03 8 (c) (i) Calculate the amount, in moles, of copper( II) sulfate in solution R that was added to the solution in the polystyrene cup in (a). amount of copper(II) sulfate = ………………… mol [1] (ii) Show that the amount of zinc you added was in excess. [Ar of zinc: 65] [2] (d) The formula for heat energy is as follow: heat energy = 𝑚 × 𝑐 × 𝜃 where 𝑚 : mass of solution (g) 𝑐 : specific heat capacity (J/goC) 𝜃 : rise in temperature (oC) Use your answer to (b)(ii) to calculate the heat energy, in joules, given out when T was added to R. Give your final answer correct to 3 significant figures. You can assume that the mass of solution is