YIJC 2023 H2 Chem Prelim P2 Student s Copy (1)

©YIJC [Turn over YISHUN INNOVA JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CG INDEX NO CHEMISTRY Paper 2 Structured Questions Candidates answer on the Question Paper. Additional Materials: Data Booklet 9729/02 28 August 2023 2 hours READ THESE INSTRUCTIONS FIRST This document consists of 23 printed pages and 3 blank pages. For Examiner’s Use 1 / 9 2 / 8 3 / 8 4 / 8 5 / 12 6 / 20 7 / 10 Penalty units significant figures Overall / 75 Write your name , CG and Index number in the spaces at the top of this page. 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, highlighters, glue or correction fluid/tape. 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. You are advised to show all working in calculations. The number of marks is given in brackets [ ] at the end of each question or part question.

©YIJC [Turn over 2 Answer all the questions in the spaces provided. 1 Semiconductors are made from a variety of raw materials. Through a complex process, semiconductor grade silicon of high purity can be produced by refining the raw materials. (a) An unknown element R was studied for its semiconductor properties. The table below shows the ionisation energies of element R. Table 1.1 1st 2nd 3rd 4th 5th 6th 7th Ionisation Energy/kJ mol–1 945 2026 2987 4144 6593 7880 14 990 The principal quantum number of Element R is n. Predict, with explanation, the Group where element R will be found in and complete its electronic configuration. Group: ………………………….. Electronic configuration: ………………………………………………. ………………………………………………………..……………………………………………..... ………………………………………………………..……………………………………………..... ………………………………………………………..……………………………………………..... [2] (b) Silicon is commonly used in semiconductors. One important raw material for semiconductors is silane (SiH 4), which is a key precursor in the production of semiconductor-grade silicon. (i) Draw the dot-and-cross diagram of silane. State the molecular shape about the central Si atom in silane. [2]

©YIJC [Turn over 3 (ii) Is silane molecule polar or non polar? Give a reason for your answer. …………………………………………………………………………………………………… …………………………………………………………………………………………………… [1] (c) The chlorides of silicon share similar properties as the chlorides of aluminium and phosphorus when they are dissolved in water. With the aid of equations, explain how chlorides of aluminium, silicon, and phosphorus exhibit acidic properties when dissolved in water. ……………………………………………………………………………………………….………… ……………………………………………………………………………………………….………… ……………………………………………………………………………………………….………… ……………………………………………………………………………………………….………… ……………………………………………………………………………………………….………… ………………………………………………………………………………………….……………… ………………………………………………………………………………………….……………… ………………………………………………………………………………………….……………… ……………………………………………………………………………………….………………… …………………………………………………………………………………….…………………… ………………………………………………………………………………….……………………… [4] [Total: 9]

©YIJC [Turn over 4 2 (a) The pKb value of three bases at 25 °C are shown in Table 2.1. Table 2.1 base formula pKb diethylamine (CH3CH2)2NH 2.9 ethylamine CH3CH2NH2 3.3 phenylamine C6H5NH2 9.4 (i) State the relationship between pKb and the strength of a base. ………….………………………………………………………………………………….…. [1] (ii) Explain the relative magnitudes of the pKb values in Table 2.1. …………………………………………………………………………………….…………..… …………………………………………………………………………………….…………..… …………………………………………………………………………………….…………..… …………………………………………………………………………………….…………..… …………………………………………………………………………………….…………..… …………………………………………………………………………………….…………..… …………………………………………………………………………………….…………..… …………………………………………………………………………………….…………..… …………………………………………………………………………………….…………..… …………………………………………………………………………………….…………..… …………………………………………………………………………………….…………..… …………………………………………………………………………………….………… [4]

©YIJC [Turn over 5 BLANK PAGE

©YIJC [Turn over 6 (b) Preparation of N -phenylethanamide can be carried out by acylation reaction of phenylamine with ethanoic anhydride. The reaction is performed in two stages I. An excess of sodium ethanoate is heated with 1.5 g of phenylammonium chloride forming phenylamine, ethanoic acid and sodium chloride. C6H5NH3Cl + CH3COONa ⟶ C6H5NH2 + CH3COOH + NaCl Mr: 129.5 Mr: 93.0 II. Phenylamine then reacts with excess of ethanoic anhydride to form 1.12 g of N-phenylethanamide (as a white solid), together with ethanoic acid. (i) Calculate the percentage yield of N-phenylethanamide. [1] (ii) Student A wanted to use sodium hydroxide instead of sodium ethanoate in stage I to produce phenylamine. Suggest an equation for the reaction between phenylammonium chloride and sodium hydroxide to form phenylamine. …………………………………………………………………………………….………….. [1]

©YIJC [Turn over 7 (iii) Student B claimed that the percentage yield of N -phenylethanmide will be affected by using sodium hydroxide instead of sodium ethanoate in stage I. Suggest and explain if Student B’s claim is correct. …………………………………………….………………………………………….………….. …………………………………………….………………………………………….………….. …………………………………………….……………………………………….….……..… [1] [Total: 8]

©YIJC [Turn over 8 3 Transesterification involves the conversion of one ester into another through the exchange of an – OR group, forming a new ester. A general reaction scheme is shown in F.g. 3.1. Fig. 3.1 Non-edible oils such as castor oil contain components such as triricinolein that can undergo transesterification with methanol to produce methyl esters and glycerol, in Fig. 3.2. The values k1 and k2 refer to the relative rate constants for the forward and reverse reactions respectively. Fig. 3.2 (a) (i) The reaction shown in Fig 3.2 is at dynamic equilibrium. Explain what is meant by dynamic equilibrium in terms of k1 and k2. …………………………………………….………………………………………….………….. …………………………………………….………………………………………….………….. …………………………………………….……………………………………….….……… [1] (ii) The equilibrium constant, Kc, is related to the ratio of k1 and k2. Prove that Kc = 𝑘1 𝑘2 [1]

©YIJC [Turn over 9 Some data regarding the reversible reaction is provided in Table 3.3 Table 3.3 Temperature/ K k1 k2 308.15 7.10 x 10-4 7.98 x 10-2 318.15 1.02 x 10-3 3.14 x 10-2 328.15 1.65 x 10-3 1.48 x 10-2 338.15 2.06 x 10-3 1.61 x 10-2 (iii) Calculate the Kc values and explain whether transesterification is endothermic or exothermic. [2]

©YIJC [Turn over 10 (b) The intermediates for the stepwise mechanism of transesterification of the acid -catalysed transesterification are shown in Fig 3.4. Fig. 3.4 (i) State the types of reaction in Steps 1 and 2. Step 1: ………………………………………………………………………………………….. Step 2: ………………………………………………………………………………………. [2] (ii) In the presence of a base such as sodium hydride, transesterification can proceed with the generatio