Copy of SKSS Chem Prelim Paper 3 + CI & MS

1 Name and Index Number: ( ) Class: SENG KANG SECONDARY SCHOOL 2024 PRELIMINARY EXAMINATION CHEMISTRY 6092/03 Secondary 4 Express 1 August 2024 Paper 3 Practical 1 hour 50 minutes Candidates answer on the Question Paper. Additional Materials: As listed in the Confidential Instructions READ THESE INSTRUCTIONS FIRST Write your index number and name on all the work you hand in. Give the details of the practical shift and laboratory where appropriate, in the boxes provided. Write in dark blue or black pen. You may use a soft pencil for any diagrams or graphs. Do not use staples, paper clips, highlighters, 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 page 10. 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 / 18 2 / 18 3 / 4 Total / 40 % / Grade Parent’s / Guardian’s Signature: ………………….…………... This document consists of 10 printed pages. Do not turn over the page until you are told to do so.

2 1 A student suggests that the concentration of sulfuric acid can be determined by measuring the temperature of the solution as the acid is added in small amounts to a known volume of sodium hydroxide solution in a styrofoam cup. 2NaOH(aq) + H2SO4(aq) → Na2SO4(aq) + 2H2O(l) The student proposes the following hypothesis. ‘As the acid is added to the alkali, the temperature rise will be directly proportional to the volume of acid added until the end -point of the reaction is reached. Upon further addition of acid there will be a reduction in the temperature of the solution in the cup as the acid added is not reacting and is at a lower temperature than the solution in the styrofoam cup.’ The following reagents are provided. A is approximately 0.75 mol/dm3 sulfuric acid, H2SO4. B is 2.00 mol/dm3 sodium hydroxide, NaOH. (a) Use the equation to estimate the volume of A that will neutralise 25.0 cm3 of B. volume of A = ………………………………. [1] (b) In this experiment, you will be adding A from a burette to 25.0 cm 3 of B in a styrofoam cup and measuring the temperature of the solution after each addition of a certain volume of A. In order to obtain precise information about the end -point of the reaction, you will need to decide on the: • volume of A to be added each time (do not use a volume which is less than 2.00 cm3), • total volume of A to be added. volume of A to be added each time = ………………………… total volume of A to be added = ………………………… [2]

3 (c) Read all the instructions below carefully before starting the experiments in this part of the question. Instructions Place a styrofoam cup into a 250 cm3 glass beaker. Put A into a burette. Pipette 25.0 cm3 of B into the styrofoam cup. Measure and record the temperature of B in the styrofoam cup in Table 1.1. Add the first volume of A from the burette into the styrofoam cup. Stir, using the thermometer, and measure the highest temperature reached. Record this temperature in Table 1.1. Using your answers in (b), continue to add volume of A and for each addition, record the highest temperature in Table 1.1. Complete your results in Table 1.1. Table 1.1 experiment total volume of A added / cm3 initial temperature of B / °C highest temperature of mixture / °C temperature rise / °C 1 0.00 2 3 4 5 6 7 8 [4]

4 (d) Using your results in Table 1.1, plot a graph of temperature rise against the volume of A added on the grid. Use these points to draw two intersecting straight lines of best fit. [4]

5 (e) (i) Use your graph to obtain a value for the volume of A added at the end -point of the titration. Show clearly on the graph how you obtained your answer. volume of A at the end-point = ………………………… [1] (ii) Use your answer to (e)(i) to calculate the concentration, in mol/dm 3, of H2SO4 in A. Show your working clearly. concentration of A = ………………………… [1] (f) Explain how the results in Table 1.1 and/or graph support or do not support each part of the hypothesis proposed by the student. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. [2] (g) The student, carrying out the experiment, noticed that each subsequent temperature rise became less as the reaction was approaching the end-point. Give one reason why this was the case. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. [1] (h) Another student put forward the hypothesis that the heat energy produced in the reaction, rather than the temperature rise, is proportional to the volume of acid added. Calculate the total heat produced by the addition of A at the end-point. Assume that it takes 4.2 J to raise the temperature of 1.0 cm3 of solution by 1.0 °C. heat produced = ………………………… J [2] [Total: 18]

6 2 Copper(II) sulfate, CuSO4, is used as a drying agent in the anhydrous form. (a) Hydrated copper(II) sulfate has the chemical formula CuSO 4•xH2O, where x can range from 0 to 5. When x is 0, the compound exists as the anhydrous form of copper( II) sulfate, and when x is a whole number ranging between 1 to 5, it exists as the hydrated form of copper(II) sulfate. When hydrated copper( II) sulfate is heated, it loses its water of crystallisation to form anhydrous copper(II) sulfate as shown in the equation. CuSO4•xH2O(s) → CuSO4(s) + xH2O(g) You are going to determine the value of x in the sample of hydrated copper( II) sulfate provided. Read all the instructions below carefully before starting the experiment in Question 2. R1 is hydrated copper(II) sulfate, CuSO4•xH2O. 1. Use the electronic balance to measure and record the mass of an empty boiling tube. 2. Transfer all solid R1 to the boiling tube. Measure and record the mass of the boiling tube and its contents. 3. Gently heat the boiling tube and its contents for 3 minutes. It is important that R1 is heated gently to achieve accurate results. Record your observations in (a)(i). 4. Leave the boiling tube and its contents to cool to room temperature. You may start working on Question 2(e) whilst you are waiting for the boiling tube to cool. 5. Reweigh the boiling tube and its contents and record the mass. 6. Record all your results in an appropriate format in (a)(ii). (i) observations ……………………………………………………………………………………….. ……………………………………………………………………………………….. [1] (ii) results [3]

7 (iii) From your results in (a)(ii), determine the mass of R1 before heating ……………………………………………………. the mass of anhydrous CuSO4 after heating …………………………………… [2] (b) (i) Calculate the amount, in mol