2024 ASRJC H2 Chemistry Prelim P4 (Ans)

ASRJC JC2 PRELIM 20248 9729/04/H2 [Turn Over ANDERSON SERANGOON JUNIOR COLLEGE 2024 JC 2 PRELIMINARY EXAMINATION NAME:________________________________ ( ) CLASS: 24 /____ CHEMISTRY 9729/04 Paper 4 Practical SUGGESTED SOLUTIONS

2 ASRJC JC2 PRELIM 20248 9729/04/H2 Answer all the questions in the spaces provided. 1 Investigation of the kinetics of the catalysed decomposition of hydrogen peroxide Hydrogen peroxide decomposes very slowly to form water and oxygen gas as shown in equation 1. equation 1 2H2O2 2H2O + O2 Many transition element ions are able to catalyse the decomposition of hydrogen peroxide. Iron(III) nitrate, Fe(NO3)3, is an effective catalyst for this reaction. FA 1 is 0.170 mol dm-3 aqueous hydrogen peroxide, H2O2 FA 2 is 0.2 mol dm-3 sulfuric acid, H2SO4 FA 3 is 0.020 mol dm-3 potassium manganate(VII), KMnO4 You are also provided with iron(III) nitrate, Fe(NO3)3 You will add a measured volume of iron(III) nitrate to a measured volume of FA 1 and, at timed intervals, transfer aliquots (portions) of the reaction mixture to titrate remaining H 2O2 against KMnO4 in FA 3. Acidified KMnO4 and H2O2 react as shown in equation 2. equation 2 2MnO4–(aq) + 5H2O2(aq) + 6H+(aq) 2Mn2+(aq) + 8H2O(l) + 5O2(g) (a) (i) Preparation and titration of the reaction mixture Notes: You will perform each titration once only. Great care must be taken that you do not overshoot the end-point. Once you have started the stopwatch, it must continue running for the duration of the experiment. You must not stop it until you have finished this experiment. You should aim to transfer your first aliquot within the first three minutes of starting the reaction. You should aim not to exceed a maximum reaction time of 25 minutes for this experiment. In an appropriate format in the space provided, prepare a table to record for each aliquot • the time of transfer, t, in minutes and seconds, • the decimal time, td, in minutes, to 0.1 min, for example, if t = 4 min 33 s then td = 4 min + 33/60 min = 4.6 min, • the burette readings and the volume of FA 3 added.

3 ASRJC JC2 PRELIM 2024 9729/04/H2 [Turn Over 1. Fill a burette with FA 3. 2. Using a measuring cylinder, add 100.0 cm 3 of FA 1 to the conical flask labelled reaction mixture. 3. Using a measuring cylinder, add 2.0 cm3 of iron(III) nitrate , in one portion, to the same conical flask. Start the stopwatch and swirl the mixture thoroughly to mix its contents. 4. Using a measuring cylinder, add 50.0 cm3 of FA 2 to a second conical flask. 5. Transfer a 10.0 cm 3 aliquot (portion) of the reaction mixture to a 10 cm 3 measuring cylinder, using another dropping pipette. 6. Immediately transfer this aliquot into the second conical flask and vigorously swirl the mixture. Read and record the time of transfer in minutes and seconds,