2024 Prelims DHS H2 Chem P2 (Ans)

© DHS 2024 9729/02 [Turn over Suggested Solutions DUNMAN HIGH SCHOOL Preliminary Examination Year 6 H2 CHEMISTRY Paper 2 Structured Questions Candidates answer on the Question Paper. Additional Materials: Data Booklet 9729/02 11 September 2024 2 hours READ THESE INSTRUCTIONS FIRST Write your centre number, index number, name and class at the top of this page. 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. A Data Booklet is provided. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use 1 11 2 12 3 11 4 16 5 25 Total 75 This document consists of 19 printed pages.

2 © DHS 2024 9729/02 1 (a) The concentration of aluminium ions in a water sample can be determined accurately by titrating it with a solution of EDTA4–. The representative balanced equation for the reaction between aluminium ions and EDTA4– is shown below. Al3+(aq) + EDTA4–(aq) → [Al(EDTA)]–(aq) A 10.0 cm3 water sample is transferred to a 250 cm3 volumetric flask and made up to the mark with deionised water. An aliquot of 25.0 cm3 is pipetted and titrated with 0.0200 mol dm –3 EDTA4–. 35.45 cm3 of this EDTA4– solution is required for complete reaction with the aluminium ions. (i) Calculate the amount of EDTA4– that reacted with the aluminium ions. [1] No. of moles of EDTA4– = 0.0200 × 35.45 1000 = 7.09 × 10–4 mol (ii) Calculate the amount of aluminium ions in the water sample. [1] No. of moles of Al3+ in 25.0cm3 = 7.09 × 10–4 mol No. of moles of Al3+ in 250cm3 = 7.09 × 10–4 × 250 25 = 7.09 × 10–3 mol (b) The process of anodising aluminium increases its resistance to wear and corrosion. (i) State the two half -equations in the anodising of aluminium and the overall equation to form the protective layer. [2] At the cathode: 2H+(aq) + 2e– → H2(g) At the anode: 2H2O(l) → O2(g) + 4H+(aq) + 4e– The O2(g) evolved at the anode then reacts with Al metal to form Al2O3(s): 4Al(s) + 3O2(g) → 2Al2O3(s) (ii) Draw a labelled diagram to show the cell set-up used to anodise aluminium. Include details of the cathode, anode and electrolyte. [1]

3 © DHS 2024 9729/02 [Turn over (c) Aluminium chloride is used extensively as a Lewis acid catalyst in organic reactions with the notable example of Friedel–Crafts alkylation of arenes. (i) State the type of reaction occurring in Friedel–Crafts alkylation. [1] Electrophilic substitution (ii) In the presence of aluminium chloride, phenylam