SKSS 4E Chem Prelim P2 2024

[Turn over Name and Index Number: ( ) Class: SENG KANG SECONDARY SCHOOL 2024 PRELIMINARY EXAMINATION CHEMISTRY 6092/02 Secondary 4 Express 21 August 2024 Paper 2 1 hour 45 minutes Candidates answer on the Question Paper. No Additional Materials are required. READ THESE INSTRUCTIONS FIRST Write your index number and name 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, highlighters, glue or correction fluid. Section A Answer all questions. Write your answers in the spaces provided. Section B Answer any one question. Write your answers in the spaces provided. 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 22. The use of an approved scientific calculator is expected, where appropriate. For Examiner’s use Section A / 70 1 / 6 2 / 12 3 / 9 4 / 12 5 / 11 6 / 8 7 / 12 Section B / 10 8 / 10 9 / 10 Total / 80 Total % / 100 Parent’s / Guardian’s Signature: ………………….…………... This document consists of 22 printed pages. Do not turn over the page until you are told to do so.

2 [Turn over Section A [70 marks] Answer all the questions in this section in the spaces provided. 1 Choose from the list of compounds to answer these questions. aluminium nitrate ammonia calcium hydroxide carbon dioxide ethanol methane sulfur dioxide sulfuric acid water Each compound may be used once, more than once or not at all. Identify the compound that: (a) is a common solvent for chromatography in the laboratory, …………………………………………………………………………………………… [1] (b) is used to test for the presence of carbon dioxide, …………………………………………………………………………………………… [1] (c) decolourises acidified aqueous potassium manganate(VII), …………………………………………………………………………………………… [1] (d) gives white precipitate which dissolves in excess aqueous sodium hydroxide, …………………………………………………………………………………………… [1] (e) is a product of Haber Process, …………………………………………………………………………………………… [1] (f) is a waste gas from digestion in animals. …………………………………………………………………………………………… [1] [Total: 6]

3 [Turn over 2 This question is about metals and some metal compounds. (a) Chromium is a transition metal. Sodium is an element in Group 1 of the Periodic Table. State two physical properties of chromium that are different to those of sodium. 1. ………………………………………………………………………………………… 2. ………………………………………………………………………………………… [2] (b) The symbols for two isotopes of chromium are shown. Cr24 52 Cr24 53 Complete Table 2.1 to show the number of subatomic particles in these two isotopes of chromium. Table 2.1 Cr24 52 Cr24 53 number of electrons number of neutrons number of protons [2] (c) Chromium(III) oxide is reduced by carbon, under high temperature, to produce chromium and carbon dioxide. (i) Construct a balanced chemical equation for this reaction. State symbols are not required. …………………………………………………………………………………….. [1] (ii) Chromium(III) oxide is classified as an amphoteric oxide but carbon dioxide is classified as an acidic oxide. Explain the meaning of the terms amphoteric and acidic as applied to these oxides. Include one equation in your explanation. …………………………………………………………………………………….. …………………………………………………………………………………….. …………………………………………………………………………………….. …………………………………………………………………………………….. [2]

4 [Turn over (d) A coloured crystal of chromium( III) nitrate is placed at the bottom of a beaker containing water. Colour spreads throughout the water overtime. Fig. 2.2 shows the spread of colour after two days. at the start after 2 hours after 2 days Fig. 2.2 Explain these observations. ……………………………………………………….………………………………….. ……………………………………………………….………………………………….. ……………………………………………………….………………………………….. ……………………………………………………….………………………………….. ……………………………………………………….………………………………….. ……………………………………………………….………………………………….. [3] (e) Table 2.3 shows the observations made when four different metals are heated in oxygen. Table 2.3 metal observations lanthanum forms a layer of oxide rapidly on the surface but does not burn mercury does not form a layer of oxide on the surface nickel forms a layer of oxide slowly on the surface but does not burn sodium burns rapidly Using the information in Table 2.3 to suggest the order of reactivity of these metals. most least reactive ……….….……, …….….………, ….…….………, ……...….…… reactive [2] [Total: 12] water crystal of chromium(III) nitrate

5 [Turn over 3 (a) Iodine reacts with chlorine to form iodine monochloride, ICl. Draw a ‘dot and cross’ diagram for a molecule of iodine monochloride. Show outer electrons only. [1] Iodine monochloride is a useful reagent in organic synthesis. (b) Iodine monochloride reacts in a similar way to bromine. It can undergo addition reaction with ethene. This reaction gives an enthalpy change of −94 kJ/mol. (i) Draw the displayed formula of the product of this reaction. [1] (ii) Table 3.1 shows some of the bond energies. Table 3.1 bond bond energy / (kJ/mol) C―C 348 C═C 614 C―Cl 328 C―H 413 C―I 240 I―Cl ? Calculate the bond energy of I―Cl. bond energy of I―Cl = ……………………... [2]

6 [Turn over (iii) Complete the energy profile diagram in Fig. 3.2 for this reaction. The energy profile diagram should include: • the chemical formula of the product, • labels to show the activation energy and the enthalpy change of reaction. progress of reaction [3] Fig. 3.2 (c) Iodine monochloride also reacts in a similar way to chlorine. Iodine monochloride reacts with ethane in the presence of ultraviolet light. (i) State the type of reaction that takes place. …………………………………………………………………………………….. [1] (ii) Construct a chemical equation for the reaction between iodine monochloride and ethane. …………………………………………………………………………………….. [1] [Total: 9] energy C2H4 + ICl

7 [Turn over 4 A sample of clean, dry air contains 0.0400% carbon dioxide by volume. (a) Calculate the number of molecules of carbon dioxide in 480 dm3 of clean, dry air at room temperature and pressure. number of molecules = ……………………. [2] (b) Complete combustion of fuels such as petrol makes carbon dioxide. The percentage by mass of the elements present in petrol is given in Table 4.1. Table 4.1 element percentage by mass carbon hydrogen 85.7 14.3 (i) Calculate the empirical formula of petrol. [2] (ii) The molecular mass of petrol is 128.25. Hence, calculate the molecular formula of petrol. [1]

8 [Turn over (iii) If 1 kg of petrol is burnt