2024 RVHS H2 Chemistry Prelim P4 (QP)

RIVER VALLEY HIGH SCHOOL JC 2 PRELIMINARY EXAMINATION H2 CHEMISTRY 9729 Paper 4 20 AUGUST 2024 2 HOURS 30 MINUTES NAME CLASS 23J ( ) INDEX NO. INSTRUCTIONS TO CANDIDATES DO NOT OPEN THIS BOOKLET UNTIL YOU ARE TOLD TO DO SO. Read these notes carefully. Write your name, class and index number 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 a 2B pencil for any diagram or graph. 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. Shift Laboratory For Examiner’s Use s.f. Units Total 55 _______________________________________________________________________________ This Question Paper consists of 20 printed pages.

River Valley High School Pg 2 of 20 JC 2 H2 Chemistry 9729 2024 Preliminary Examination Paper 4 Answer all the questions in the spaces provided. 1 To determine the percentage by mass of Fe(NO3)2 in a salt mixture FA 1 is a solution containing a salt mixture of two different ionic compounds. One of the compounds is Fe(NO3)2. In this question, you will determine the percentage by mass of Fe(NO3)2 in the mixture by preparing a diluted solution of FA 1 and carry out a titration using potassium manganate(VII). The iron(II) ions, Fe2+, are oxidised by the manganate(VII) ions, MnO4−. 5Fe2+(aq) + MnO4−(aq) + 8H+(aq) → 5Fe3+(aq) + Mn2+(aq) + 4H2O(l) The end-point of the titration occurs when the presence of unreacted MnO4− causes the colour of the solution to become orange. The following reagents are provided. FA 1 is a solution containing 125.4 g dm−3 of the salt mixture in sulfuric acid. FA 2 is 0.0100 mol dm−3 manganate(VII) ions, MnO4−. FA 3 is 1.00 mol dm−3 sulfuric acid, H2SO4. (a) Determining the percentage by mass of Fe(NO3)2 1. Fill a burette with FA 2. 2. Use a pipette to transfer 25.0 cm3 of FA 1 into a 250 cm3 volumetric flask. 3. Make up to the mark with deionised water and label this solution FA 4. Shake to obtain a homogeneous solution. 4. Pipette 25.0 cm3 of FA 4 into a 250 cm3 conical flask. 5. Use the 25.00 cm3 measuring cylinder to add 25.00 cm3 of FA 3 into the conical flask. FA 3 is added in excess. 6. Run FA 2 from the burette into the conical flask. The end-point is reached when the solution changes colour from yellow to orange. 7. Record your titration results , to an appropriate level of precision, in the space provided on the next page. 8. Repeat steps 4 to 7 until consistent titre values are obtained.

River Valley High School Pg 3 of 20 JC 2 H2 Chemistry 9729 2024 Preliminary Examination Paper 4 Results 1 2 3 4 5 (b) From y our titrations, obtain a suitable volume of FA 2 to be used in your calculations. Show clearly how you obtained this volume. volume of FA 2 used = …………………………….. 6 (c) (i) Calculate the amount of MnO4− used in the titration. amount of MnO4− = …………………………….. 7 (ii) Calculate the amount of Fe2+ ions present in 25.0 cm3 of FA 4. amount of Fe2+ = …………………………….. 8

River Valley High School Pg 4 of 20 JC 2 H2 Chemistry 9729 2024 Preliminary Examination Paper 4 (iii) Calculate the concentration of Fe2+ ions present in FA 1. concentration of Fe2+ = …………………………….. 9 10 (iv) Hence, calculate the percentage by mass of Fe(NO3)2 in the salt mixture. [Ar: Fe, 55.8; N, 14.0; O, 16.0] percentage by mass of Fe(NO3)2 = …………………………….. 11 (d) A student repeated the experiment but used a sample of FA 1 prepared in water instead of sulfuric acid. Explain how this would affect the titre value. ………………………………………………………………………................................. ………………………………………………………………………................................. 12

River Valley High School Pg 5 of 20 JC 2 H2 Chemistry 9729 2024 Preliminary Examination Paper 4 (e) The end -point of the titration is reached when the solution in the conical flask changes colour from yellow to orange. (i) Account for the colour change with reference to the chemical species present. ………………………………………………………………………........................ ………………………………………………………………………....................... ………………………………………………………………………........................ 13 (ii) Hydrogen peroxide is also able to oxidise the Fe2+ ions in an acidic medium. However, it is not a suitable replacement for KMnO 4 in this experiment. Suggest a reason for this. ………………………………………………………………………........................ ………………………………………………………………………........................ 14 (f) A student carried out the experiment and obtained an FA 2 titre of 29.70 cm3 for the end-point. The absolute uncertainties associated with each apparatus are given below. pipette 0.06 cm3 burette 0.05 cm3 25.0 cm3 measuring cylinder 0.25 cm3 (i) Use the given data to calculate the percentage uncertainty associated with each apparatus. ………………………………………………………………………........................ ………………………………………………………………………....................... ………………………………………………………………………........................ 15 (ii) Hence, identify the apparatus that gives rise to the highest percentage uncertainty in the student’s titre value. ………………………………………………………………………........................ 16 [Total: 16]

River Valley High School Pg 6 of 20 JC 2 H2 Chemistry 9729 2024 Preliminary Examination Paper 4 2 Determination of the kinetics of the reaction between iron(III) ions and iodide ions In acidic solutions, iron(III) ions are reduced by iodide ions to form iron(II) ions . The iodide ions are oxidised to iodine. 2Fe3+(aq) + 2I–(aq) → 2Fe2+(aq) + I2(aq) The rate of this reaction can be investigated by using starch indicator, which turns blue-black in the presence of iodine. Sodium thiosulfate is added to the reaction mixture to react with iodine as it is formed. The blue-black colour is seen when all the thiosulfate has reacted. I2(aq) + 2S2O32–(aq) → 2I–(aq) + S4O62–(aq) You will investigate how the rate of reaction is affected by changing the concentration of the iodide ions. In this series of experiments, the rate equation for the reaction can be simplified to rate = k’ [I–]m, where m is the rate order with respect to [I–] and k’ is k[Fe3+]. The simplified rate equation can be further manipulated to derive the following relationship: lg(rate) = m  lg(volume of FA 6) + constant FA 5 is 0.0500 mol dm–3 iron(III) chloride, FeCl3. FA 6 is 0.0500 mol dm–3 potassium iodide, KI. FA 7 is 0.00500 mol dm–3 sodium thiosulfate, Na2S2O3. FA 8 is starch indicator. (a) Method Prepare a table on page 7 for your results. You will need to include the volume of FA 6, volume of water, reaction time, lg(volume of FA 6) and lg(rate) for each of the four experiments. Record all calculated values to 3 significant figures. Experiment 1 1. Use a 25.00 cm 3 measuring cylin der to place 20.00 cm3 of FA 6 in a 100 cm3 beaker. 2. Use appropriate measuring cylin ders to add the following to the same beaker. • 20.0 cm3 of FA 7 • 10.0 cm3 of FA 8 3. Use an appropriate measuring cylinder to measure 10.0 cm3 of FA 5. 4. Add this FA 5 to the same 100 cm3 beaker and start timing immediately. 5. Stir the mixture and place the beaker on a white tile. 6. Stop timing as soon as the solution turns blue-black. 7. Record this reaction time to the nearest 0.1 second. 8. Wash the beaker and dry it with a paper towel.

River Valley High School Pg 7 of 20 JC 2 H2 Chemistry 97