2024 Prelims YIJC H2 Chem P3 (QP)

©YIJC [Turn over YISHUN INNOVA JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CG INDEX NO CHEMISTRY Paper 3 Free Response Candidates answer on the Question Paper. Additional Materials: Data Booklet 9729/03 12 September 2024 2 hours READ THESE INSTRUCTIONS FIRST This document consists of 32 printed pages. For Examiner’s Use Section A 1 / 21 2 / 18 3 / 21 Section B 4 or 5 / 20 Penalty units significant figures Overall / 80 Write your name, class and index number on all the work you hand in. Write in dark blue or black pen on both sides of the paper. 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. If additional space is required, you should use the pages at the end of this booklet. The question number must be clearly shown. Section A Answer all the questions. Section B Answer one question. The use of an approved scientific calculator is expected, where appropriate. A Data Booklet is provided. 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.

2 ©YIJC [Turn over Section A Answer all the questions in this section. 1 (a) The tripeptide A is made by reacting amino acids B, C and D together. Table 1.1 shows the pKa values of the different functional groups present on each amino acid. Table 1.1 amino acid pKa of –carbonyl group pKa of –amino group pKa of side chain B 2.09 9.10 − C 1.88 9.60 3.65 D 2.02 8.80 − (i) Explain the term -amino acid. [1] (ii) One of the amino acids, B, present in the tripeptide A contains more than one chiral carbon atom. Draw the displayed formula of B. [1] (iii) Draw the predominant species of C at pH 4.0. [1] (iv) Suggest a pH at which the predominant species of C is a zwitterion using the information in Table 1.1. [1] (v) Explain why the side-chain of D does not have a Ka value. [1]

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4 ©YIJC [Turn over (b) 1,2-diaminopropane can be synthesised from propene by the following route. (i) Outline the mechanism for step 1 to show the formation of 1-bromo-2-chloropropane. Show all charges, relevant lone pairs and show the movement of electron pairs using curly arrows. [2] (ii) Use your mechanism to explain the preferential production of 1-bromo-2-chloropropane over 2-bromo-1-chloropropane. [1] (iii) State the reagents and conditions for step 2. [1] (iv) 1,2-diaminopropane can react with bromoethane to form compound E, C7H18N2. Suggest the structure for E. [1]

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6 ©YIJC [Turn over (c) Alkanes are very unreactive. However, alkanes such as butane, C 4H10, do react with chlorine. There are two possible monochloroalkanes that can be formed from butane. One of the monochloroalkanes exhibits stereoisomerism. (i) Suggest two reasons why alkanes are generally unreactive. [2] (ii) Predict the relative proportions of 1 -chlorobutane and 2-chlorobutane that are likely to be produced from C4H10. Explain your answer. [2] (iii) Draw three-dimensional structures for the two stereoisomers of the monochloroalkane formed from the chlorination of butane. [1]

7 ©YIJC [Turn over (d) Use the data in Table 1.2, together with relevant data from the Data Booklet, to calculate the average bond energy of the Si-Cl bond in SiCl4. Show your working. Table 1.2 enthalpy change of vaporisation of SiCl4 molecules, SiCl4(l) → SiCl4(g) = +29 kJ mol−1 standard enthalpy change of atomisation of Si(s) = +338 kJ mol−1 standard enthalpy change of formation of SiCl4(l) = −687 kJ mol−1 [3]

8 ©YIJC [Turn over (e) Describe the reaction of SiCl4 with water, stating the pH of the resulting mixture. [1] (f) Elements in Group 17 are known as the halogens. State how the reactivity of the halogens as oxidising agents varies down the group, and relate this variation to relevant Eo values. [2] [Total: 21]

9 ©YIJC [Turn over 2 (a) Alnico alloys are known for its strong magnetic properties and are commonly used in applications like permanent magnets and electronic devices. Alnico alloys contain metals such as aluminum, magnesium, iron, and cobalt. The densities of the four metals present in Alnico are given in Table 2.1. Table 2.1 metal 1 metal 2 metal 3 metal 4 density / g cm−3 1.74 2.70 7.87 8.83 (i) Explain why iron and cobalt have a higher melting point than aluminium and magnesium.[1] (ii) State which two of the metals, Mg, Al, Fe and Co, which are present in Alnico, are metals 3 and 4. Explain why. [2]

10 ©YIJC [Turn over (b) The iron( II) complex, ferrous bisglycinate hydrochloride is sometimes prescribed, in capsule form, to treat iron deficiency or anaemia. A capsule containing 500 mg of this iron( II) complex was dissolved in dilute H 2SO4 and titrated with 0.0200 mol dm–3 KMnO4. 18.10 cm3 of KMnO4 solution were required to oxidise all the Fe2+ present in the capsule. Calculate the molar mass of the iron(II) complex given that the ratio of Fe2+ to the complex is 1:1. [2]