2022 TSS Chem Prelims P2 SectA

Name: Index Number: Class: _______ TEMASEK SECONDARY SCHOOL Preliminary Examination 2022 Secondary 4 Express CHEMISTRY 6092/02 Paper 2 (Section A) Total duration for Sections A and B: 1 hour 45 minutes Question and Answer Booklet READ THESE INSTRUCTIONS FIRST Do not open the booklet until you are told to do so. Hand in this booklet at the end of the paper. Write your name, index number and class in all the work you hand in. Write in dark blue or black pen. 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 14. FOR EXAMINER'S USE Section A /50 This document consists of 14 printed page.

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 50. A1 All nitrates of Group II metal undergo thermal decomposition to form metal oxide, nitrogen dioxide and oxygen. (a) Describe a test to confirm that decomposition has taken place. ……………………………………………………………………………………… ……………………………………………………………………………………… ………………………………………...………………………………………….[2] (b) Table 1.1 shows the temperature at which each metal nitrate salt decomposes. Table 1.1 metal nitrate salt Temperature at which metal nitrate salt decomposes/ °C magnesium nitrate 330 calcium nitrate 500 strontium nitrate 570 barium nitrate 650 (i) Using Table 1.1, deduce the order of reactivity of the four metals. most reactive ……………………………………. ……………………………………. ……………………………………. least reactive ……………………………………. [1] (ii) Explain your answer in (b)(i). ………………………………………………………………………..……... ……………………………………………………………………..………... .…………………………………………………………………..…….....[2]

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 a mixture of the gases, methane, ammonia and water vapour in a flask. The electrodes provide electric sparks which causes chemical reactions to occur. Fig. 2.1 (a) The substances present at the start of the experiment are compounds consisting of small molecules. Explain what is meant by molecule. ……………………………………………………………………………………… ………………………………………...………………………………………….[1] (b) After one week , the experiment produced a mixture of products. The mixture of products can be analysed using paper chromatography. Four known compounds, glycine, alanine, cysteine and lactic acid, were added to the chromatogram for comparison. The chromatogram is shown in Fig. 2.2.

4 No part of the paper is to be reproduced without the approval of the Principal of Temasek Secondary School. Fig. 2.2 is not drawn to scale. Fig. 2.2 (i) From Fig. 2.2, deduce the identities of the substances present in the mixture of products. Explain your answer. …………………………………………………………………………….… …………………………………………………………………………….…. ………………………….……...……………………………………….…[2] (ii) The solvent front of the chromatogram is 140 mm away from the start line. It is also known that the R f value of lactic acid ranges from 0.67 to 0.78. Calculate the range of distances travelled by lactic acid in in the chromatogram. ………………………….……...………. mm [2]

5 No part of the paper is to be reproduced without the approval of the Principal of Temasek Secondary School. A3 Titanium is a transition metal used in the aerospace industry. It can be extracted by heating titanium(IV) chloride to 2000°C with sodium. TiCl4 + 4Na → Ti + 4NaCl (a) At room temperature and pressure, titanium(IV) chloride exists as a liquid. Explain why you would not expect titanium(IV) chloride to exist as a liquid at room temperature and pressure. ………….………………………………………………………………………… ………….………………………………………………………………………… ……….…………………………………………………………………………… .……………………………………...………………………………………….[2] (b) 40 kg of titanium chloride was added to 20 kg of sodium. Explain why titanium chloride is the limiting reactant. All workings must be shown. [3]

6 No part of the paper is to be reproduced without the approval of the Principal of Temasek Secondary School. A4 Aqueous solutions of barium nitrate, copper(II) sulfate, potassium hydroxide and sodium carbonate are stored in four bottles labelled A, B, C and D, but not necessarily in this order. Table 4.1 shows the observations based on the following procedures. Table 4.1 procedure observations Mix A with B, followed by dilute hydrochloric acid The solution remains colourless. Effervescence seen when dilute hydrochloric is added. Mix A with C, followed by dilute hydrochloric acid A green precipitate is observed. Effervescence seen and the precipitate is soluble in dilute hydrochloric acid. Mix C with D, followed by dilute hydrochloric acid A white precipitate is formed in a blue solution. The white precipitate remains when dilute hydrochloric acid is added. Using Table 4.1, identify solutions A, B, C and D. A ………………………………………………….. B ………………………………………………….. C ………………………………………………….. D ………………………………………………….. [4]

7 No part of the paper is to be reproduced without the approval of the Principal of Temasek Secondary School. A5 A student investigated the reaction between excess zinc and dilute hydrochloric acid. Zn + 2HCl → ZnCl2 + H2 The experiment was conducted twice with the same mass of zinc and same volume, but different concentrations of acid. (a) Fig. 5.1 shows how volume of hydrogen gas produced changes with time. Fig. 5.1 Describe and explain the difference in the shape of the graphs shown in Fig. 5.1. ………….………………………………………………………………………… ………….………………………………………………………………………… ……….…………………………………………………………………………… .……………………………………...……...………………………………….[2] volume of hydrogen gas produced/ cm3 time/ s

8 No part of the paper is to be reproduced without the approval of the Principal of Temasek Secondary School. (b) Another set of experiments was conducted using the same number of moles of zinc, magnesium and aluminium with excess hydrochloric acid. Fig. 5.2 shows the results for this set of experiments. Fig. 5.2 (i) Explain why the volume of hydrogen produced by zinc and magnesium is the same, but that of aluminium is much higher. ……………………………………………………………………………… ……………………………………………………………………………… …………………………………..…………………………………………. ……..………………….……...……………………………………….…[2] (ii) Compare the speed of reaction for the reaction between aluminium and acid and that of zinc and acid. Explain your answer. ……………………………………………………………………………… ……………………………………………………………………………… …………………………………..…………………………………………. ……..………………….……...……………………………………….…[2] aluminium magnesium zinc

9 No part of the paper is to be reproduced without the approval of the Principal of Temasek Secondary School. A6 To reduce emission of pollutants during the production of electricity, some countries are starting to burn natural gas instead of coal in power stations. Table 6.1 shows the amount of pollutants formed by each type of fuel. Table 6.1 type of fuel mass of pollutant formed per MJ of