2024 Prelims DHS H2 Chem P2 (QP)

© DHS 2024 9729/02 [Turn over Name: Centre/Index Number: Class: 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 20 printed pages.

2 © DHS 2024 9729/02 Answer all the questions in the spaces provided. 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] (ii) Calculate the amount of aluminium ions in the water sample. [1] (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]

3 © DHS 2024 9729/02 [Turn over (ii) Draw a labelled diagram to show the cell set-up used to anodise aluminium. Include details of the cathode, anode and electrolyte. [1] (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] (ii) In the presence of aluminium chloride, phenylamine does not form 2–methylphenylamine but forms neutral compound B instead. Suggest the structure of B and hence, explain why 2–methylphenylamine is not formed as expected. NH2 AlCl3 CH3Cl NH2 CH3 B 2-methylphenylamine + + ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………[3]

4 © DHS 2024 9729/02 (d) Using relevant data from the Data Booklet, explain whether fluorine or chlorine will have greater reactivity with aluminium. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. ……………………………………………………………………………………………....[2] [Total: 11]

5 © DHS 2024 9729/02 [Turn over 2 Carbon, nitrogen and oxygen are pivotal elements that form a vast array of organic compounds. (a) Explain the following observations. • Nitrogen has a smaller atomic radius than carbon. • Oxygen has a lower first ionisation energy than nitrogen. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. …………………………………………………………………………………………………. ……………………………………………………………………………………………....[3] Carboxylic acids, esters and ketones are examples of organic compounds containing carbon and oxygen atoms. (b) Table 2.1 shows a list of organic compounds and the p Ka values of their carboxylic acid group. Table 2.1 name structure pKa value benzoic acid O OH 4.2 4–hydroxybenzoic acid O OH OH 4.6 2–hydroxybenzoic acid O OH OH 4.1 (i) With reference to the carboxylate anion, explain why carboxylic acids are generally stronger acids than alcohols. ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………[1]

6 © DHS 2024 9729/02 (ii) Suggest a reason why • 4–hydroxybenzoic acid has a higher pKa value than benzoic acid, • 2–hydroxybenzoic acid has a lower pKa value than 4–hydroxybenzoic acid. ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………… ………………………………………………………………………………………[3] (iii) Carboxylic acids react with Group 2 elements to give an effervescence of hydrogen gas. State the role of the Group 2 elements in this reaction and describe how the reactivity of the Group 2 elements in this reaction will vary down the group. ………………………………………………………………………………………… ………………………………………………………………………………………[1]

7 © DHS 2024 9729/02 [Turn over (c) Compound W contains an ester functional group. O O W W was heated in an aqueous solution containing KMnO 4 and H 2SO4. Two organic products, compounds X and Y, were isolated. Table 2.2 contains information about these two products. Table 2.2 X Has poor solubility in dilute NaOH. Y Dissolves readily in dilute NaOH to give a crystalline solid, compound Z, after removing the solvent. Draw the structures of X, Y and Z. X Y Z [2] (d) State a reagent that can be used to distinguish cyclohexanone from ethanoic acid. This reagent should give a positive observation for cyclohexanone. O cyclohexanone Write the equation for the reaction occurring in this chemical test. reagent …………………...…………………………………………………………….......... equation ….…………………………………………………………………………….......... [2] [Total: 12]

8 © DHS 2024 9729/02 3 (a) Asparagine and threonine are essential amino acids vital for protein synthesis. NH2 COOH CONH2 2 1 NH2 COOH OH asparagine threonine (i) Draw a dipeptide structure that can be formed from asparagine and threonine. [1] (ii) Explain why the side chain of asparagine is neutral. ………………………………………………………………………………………… ………………………………………………………………………………………[1] (iii) State the oxidation state of carbon atoms labelled 1 and 2 in asparagine. carbon 1 ……………………………… carbon 2 ……………………………… [1] (iv) Threonine exists as a mixture of stereoisomers. Draw the structure of each stereoisomer of threonine. [2]

9 © DHS 2024 9729/02 [Turn over (b) L can react to form M and N as shown below. NH2 N OH O OH O NH2 NH2 O O O O O+ L M N (i) State the reagents and conditions required for the reaction to occur. ………………………………………………………………………………………[1] M is a weak diacidic base. Table 3.1 shows the pKb values of M. Table 3.1 NH2 NH2 H NH2 NH3+ pKb1 = 3.45 NH2 NH3 + H H3N NH3 pKb2 = 5.12 A 25 cm 3 sample of 0.125 mol dm −3 M w