Temasek 2024 Prelim O Chem P2 SectA QP

Name: Index Number: Class: _______ TEMASEK SECONDARY SCHOOL Preliminary Examination 2024 Secondary 4 Express CHEMISTRY 6092/02 Paper 2 (Section A) Total duration for Sections A and B: 1 hour 45 minutes Candidates answer on the Question Paper. No additional Materials are required. READ THESE INSTRUCTIONS FIRST Write your name, index number and class 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. At the end of the examination, submit Section A and B separately. The number of marks is given in brackets [ ] at the end of each question or part question. A copy of the Periodic Table is printed on page 7 in Section B. The use of an approved scientific calculator is expected, where appropriate. FOR EXAMINER'S USE Section A /70 This document consists of 20 printed pages and 2 blank pages.

2 No part of the paper is to be reproduced without the approval of the Principal of Temasek Secondary School. Section A Answer all the questions in this section in the spaces provided. The total mark for this section is 70. A1 The list below shows the chemical formulae of some substances. (NH4)2SO4 Ag2CO3 NaBr ZnCl2 CaCl2 FeSO4 Al2O3 KNO3 SiO2 Use the list to answer the questions below. The substances can be used once, more than once, or not at all. (a) State one substance that is coloured. ……………………………………………………………………………... [1] (b) State one substance that reacts with both an acid and an alkali. ……………………………………………………………………………... [1] (c) State one substance that can be prepared by precipitation. ……………………………………………………………………………... [1] (d) State one substance that is commonly used as a fertiliser. ……………………………………………………………………………... [1] (e) State one substance that is used as a catalyst in the cracking of large hydrocarbons into useful shorter fractions. ……………………………………………………………………………... [1] [Total: 5]

3 No part of the paper is to be reproduced without the approval of the Principal of Temasek Secondary School. A2 Fig. 2.1 shows the arrangement of the apparatus for an experiment that is carried out to study the reactivity of metals. Fig. 2.1 Table 2.1 shows the results obtained from the experiment using metal electrodes P, Q, R and S. Table 2.1 pair of metal electrodes voltmeter reading/ V negative terminal Q and R 2.7 metal Q R and S 1.1 metal S S and P 0.3 metal S Q and S X metal Q P and R 0.8 metal P (a) Explain, in terms of structure and bonding, why the metal electrodes can conduct electricity. ………………………...…………………………………………………... ………………………...…………………………………………………... ………………………...…………………………………………………... [2] (b) Based on Table 2.1, arrange the metals P, Q, R and S in decreasing reactivity. ……………………………………………………………………………... [1] metal electrode Q metal electrode R sulfuric acid

4 No part of the paper is to be reproduced without the approval of the Principal of Temasek Secondary School. (c) Suggest the value of X. ……………………………………………………………………………... [1] (d) Name the process that took place at the negative terminal. ……………………………………………………………………………... [1] (e) Will any reaction occur when metal P is heated with oxide of metal R? Explain your answer. ……………………………………………………………………………... ……………………………………………………………………………... [2] [Total: 7] A3 Amino acids may be separated by using two-dimensional paper chromatography. This involves putting a spot of the mixture on the corner of a piece of chromatography paper and allowing a solvent to soak up the paper. The paper is then dried, turned through 90° and placed in a second solvent. This method gives better separation than a one solvent method. Table 3.1 shows the Rf values for some amino acids in two different solvents. Table 3.1 amino acid Rf in solvent 1 Rf in solvent 2 A 0.1 0.2 B 0.0 0.4 C 0.3 0.0 D 0.8 0.9 (a) State the amino acid that is the most soluble in both solvents. ……………………………………………………………………………... [1] (b) State the amino acid which did not move at all in solvent 2. State a conclusion that you can make from this observation. ……………………………………………………………………………... [2]

5 No part of the paper is to be reproduced without the approval of the Principal of Temasek Secondary School. (c) Use the grid in Fig. 3.1 to plot the positions of the amino acids after two - dimensional paper chromatography using solvent 1 followed by solvent 2. The positions of amino acid B and C have been plotted for you. Fig. 3.1 [2] (d) Amino acids are colourless. Briefly explain what must be done before measurements of Rf values can be taken. ……………………………………………………………………………… [1] [Total: 6] spot applied here solvent front direction of solvent 1 C direction of solvent 2 solvent front B

6 No part of the paper is to be reproduced without the approval of the Principal of Temasek Secondary School. A4 Naphtha is a fraction of crude oil. The molecules in naphtha are hydrocarbons with 5 to 12 carbon atoms. Naphtha can undergo cracking in an oil refinery. (a) State an industrial use of the fraction naphtha. ……………………………………………………………………………... [1] (b) One molecule in naphtha is a saturated hydrocarbon with 5 carbon atoms. When this molecule undergoes cracking, it produces ethene and another product. Write an equation, showing full structural formulae , for this reaction. [2]

7 No part of the paper is to be reproduced without the approval of the Principal of Temasek Secondary School. (c) In another process, hexane is passed over a heated catalyst and several products are formed. Two of the products are shown below. Which one of the two products is an isomer of hexane? Explain your reasoning. ……………………………………………………………………………... ……………………………………………………………………………... ……………………………………………………………………………... [2] [Total: 5]

8 No part of the paper is to be reproduced without the approval of the Principal of Temasek Secondary School. A5 0.100 mol/dm3 sodium hydroxide solution is added from a burette to a beaker of 50.0 cm 3 of 0.100 mol/dm 3 of hydrochloric acid. The change in pH is plotted against the volume of sodium hydroxide added. In a separate experiment, the 0.100 mol/dm3 sodium hydroxide solution is added to another beaker of 50.0 cm 3 ethanoic acid and the change in pH is plotted in the same axes as show in Fig. 5.1. The colour change interval of two indicators: phenolphthalein and methyl red, are also shown in Fig. 5.1. Fig. 5.1 The equivalence point, also known as the end -point, is the point where the reactants are mixed in the right proportion according to the balanced equation. (a) Identify the graph in Fig. 5.1 that represents ethanoic acid. Explain your answer. ……………………………………………………………………………... ……………………………………………………………………………... ……………………………………………………………………………... [2] (b) State how Fig. 5.1 shows that the concentration of ethanoic acid is the same as that of hydrochloric acid. ……………………………………………………………………………... ……………………………………………………………………………... [1] Graph X Graph Y Volume of NaOH (cm3) pH

9 No part of the paper is to be reproduced without the approval of the Principal of Temasek Secondary