2024 ASRJC H2 Chem P2 (QP)

ASRJC JC2 PRELIM 2024 9729/02/H2 [Turn over ANDERSON SERANGOON JUNIOR COLLEGE 2024 JC 2 PRELIMINARY EXAMINATION NAME:______________________________ ( ) CLASS: 24 / _____ CHEMISTRY 9729/02 Paper 2 Structured Questions 11 September 2024 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, class and register number on all the work you hand in. 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. 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 Paper 2 1 /15 2 /13 3 /11 4 /16 5 /20 Total / 75 This document consists of 21 printed pages and 3 blank pages.

2 ASRJC JC2 PRELIM 2024 9729/02/H2 Answer all the questions. 1 (a) Phosphorus, sulfur and chlorine are Period 3 elements of the Periodic Table. Table 1.1 shows some properties of the three elements. Table 1.1 P S Cl number of electrons in 3p subshell number of unpaired electrons (i) Complete Table 1.1 to show the number of electrons in the 3p subshell and the number of unpaired electrons in an atom of P, S and Cl. [2] (ii) With reference to the Data Booklet, state and explain the trend of the ionic radius of P3–, S2– and Cl–. …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... ……………………………………………………………………………………………….. [2] (b) Phosphoryl chloride, POCl3, is a colourless liquid that is used to make phosphate esters. P O Cl Cl Cl POCl3 has similar chemical properties as PC l5. It has a melting point of 1 °C and a boiling point of 106 °C. It also reacts vigorously with water, forming misty fumes and an acidic solution of H3PO4. (i) Explain how the information in (b) suggests that the structure and bonding of POCl3 is simple covalent. …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... ……………………………………………………………………………………………….. [2]

3 ASRJC JC2 PRELIM 2024 9729/02/H2 [Turn over (ii) Write a balanced equation for the reaction of POCl3 with water. ……………………………………………………………………………………………….. [1] (iii) In H3PO4, there is no hydrogen atom directly bonded to the phosphorus atom. Draw the ‘dot and cross’ diagram of H 3PO4 and state the shape of the molecule with respect to P. shape: ………………………………………….. [2]

4 ASRJC JC2 PRELIM 2024 9729/02/H2 (c) Phosphoryl chloride, POC l3, is manufactured industrially from phosphorus trichloride and oxygen as shown in equation 1.1. equation 1.1 2PCl3(g) + O2(g) 2POCl3(g) The standard enthalpy changes of formation for these species are shown in Table 1.2. Table 1.2 Enthalpy change of formation of PCl3(g) −289 kJ mol–1 Enthalpy change of formation of POCl3(g) −592 kJ mol–1 (i) Define the term standard enthalpy change of formation. …………………………………………………………………………………………………... ……………………………………………………………………………………………….. [1] (ii) Using the data from Table 1.2 and relevant data from the Data Booklet, calculate the bond energy of P=O in POCl3. [2] (iii) Predict and explain the sign of the entropy change for the reaction in equation 1.1. …………………………………………………………………………………………………... …………………………………………………………………………………………………... ……………………………………………………………………………………………….. [1]

5 ASRJC JC2 PRELIM 2024 9729/02/H2 [Turn over (iv) Comment on the effect of increasing temperature on the spontaneity of the reaction in equation 1.1. …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... ……………………………………………………………………………………………….. [2] [Total: 15]

6 ASRJC JC2 PRELIM 2024 9729/02/H2 2 The structure of a tetrapeptide T is shown below. H2N O N H O H N O N H OH O OH HO O OH HO O T (a) Name the type of reaction to break T into its constituent amino acids. ………………………………………………………………………………………………………. [1] (b) The four amino acids formed from the reaction in (a) are glutamic acid, tyrosine, U and V. The structures of glutamic acid and tyrosine are as shown. glutamic acid tyrosine OH H2N O HO O OH H2N O OH Table 2.1 lists the p Ka values of the different functional groups present on each of the four amino acids. Table 2.1 Amino acid pKa -carboxyl group -amino group side chain glutamic acid 2.1 9.5 4.1 tyrosine 2.2 9.2 10.5 U 2.0 9.9 3.9 V 2.2 9.2 -

7 ASRJC JC2 PRELIM 2024 9729/02/H2 [Turn over (i) Explain why the p Ka value of the side chain of glutamic acid is lower than that in tyrosine. You may represent glutamic acid as R−CO2H and tyrosine as R OH . …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... ……………………………………………………………………………………………….. [3] (ii) In the space below, draw the structures of the predominant species of U and V at pH 3.0. U V [2] (c) Solutions containing the zwitterions of V can act as buffers. (i) State what is meant by the term zwitterion. …………………………………………………………………………………………………... ………………………………………………………………………………………………. [1] (ii) With the aid of appropriate equations, explain how a solution containing the zwitterions of V can resist pH changes. You may use H 2NCHRCOOH to represent the structure of V. …………………………………………………………………………………………………... …………………………………………………………………………………………………... …………………………………………………………………………………………………... ………………………………………………………………………………………………. [2]

8 ASRJC JC2 PRELIM 2024 9729/02/H2 (d) (i) Calculate the pH of 0.10 mol dm−3 solution of protonated V. Ignore the effect of pKa of the -amino group on the pH. [2] (ii) A student records the pH of the mixture when 20 cm3 of 0.10 mol dm-3 NaOH(aq) was added to 10.0 cm3 of 0.10 mol dm−3 solution of protonated V. Sketch the shape of the pH curve on Fig. 2.1 using all relevant information given or calculated. Your sketch should also clearly indicate the two points where the solution is most effective in resisting pH changes. Fig. 2.1 [2] [Total: 13]

9 ASRJC JC2 PRELIM 2024 9729/02/H2 [Turn over 3 (a) (i) Write an equation to represent the lattice energy of magnesium bromide, MgBr2. ………………………………………………………………………………………………. [1] (ii) Use the data in Table 3.1, to