2024 Kranji Sec Pure Chem P2

Candidate Name: __________________________ ( ) Class: _________ KRANJI SECONDARY SCHOOL Preliminary Examination Secondary 4 Express CHEMISTRY 6092/02 Paper 2 Monday 19 August 2024 1 hr 45 min KRANJI SECONDARY KRANJI SECONDARY KRANJI SECONDARY KRANJI SECONDARY KRANJI SECONDARY KRANJI SECONDARY KRANJI SECONDARY KRANJI SECONDARY KRANJI KRANJI SECONDARY KRANJI SECONDARY KRANJI SECONDARY KRANJI SECONDARY KRANJI SECONDARY KRANJI SECONDARY KRANJI SECONDARY KRANJI SECONDARY KRANJI KRANJI SECONDARY KRANJI SECONDARY KRANJI SECONDARY KRANJI SECONDARY KRANJI SECONDARY KRANJI SECONDARY KRANJI SECONDARY KRANJI SECONDARY KRANJI KRANJI SECONDARY KRANJI SECONDARY KRANJI SECONDARY KRANJI SECONDARY KRANJI SECONDARY KRANJI SECONDARY KRANJI SECONDARY KRANJI SECONDARY KRANJI 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. Section A Answer all questions. Write your answers in the spaces provided. Section B Answer 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. Set by: Mrs Toh-Chong Keting This Question Paper consists of 22 printed pages. [Turn over 4E Session 1 For Examiners’ Use Section A 70 Section B 10 Total 80

2 Section A (70 marks) Answer all the questions in this section in the spaces provided. The total mark for this section is 70. A1 The following solutions are commonly found in a science laboratory. Ba(NO3)2 H2SO4 NH3 KI AgNO3 CuSO4 Ca(OH)2 NH4Cl HNO3 Use the list above to answer the following questions. You may use each solution once, more than once or not at all. (a) Which two solutions have a pH that is more than 7? ................................................. and ................................................................... [1] (b) Which solution gives a light blue precipitate with aqueous sodium hydroxide? .............................................................................................................................. [1] (c) Which two solutions give a yellow precipitate when mixed? ................................................. and ................................................................... [1] (d) Which solution turns brown when acidified potassium manganate(VII) is added? .............................................................................................................................. [1] (e) Which solution can be added to treat soil that is too acidic? .............................................................................................................................. [1] [Total: 5]

3 [Turn over A2 Fractional distillation is a key separation technique used in both laboratory settings by students and on an industrial scale in the petroleum industry. (a) A class of students are asked to separate components in various mixtures using fractional distillation. Fig. 2.1 shows an erroneous set-up that was spotted by the teacher. Fig. 2.1 Complete Table 2.1 by filling in the description of one error and how the experiment will be affected. Table 2.1 description of error effect on experiment [2] water out water in

4 (b) Describe the separation of crude oil by fractional distillation. ….................................................................................................................................. ….................................................................................................................................. ….................................................................................................................................. ….................................................................................................................................. ….................................................................................................................................. ….................................................................................................................................. ….................................................................................................................................. ….................................................................................................................................. …………………………………………………………………………………......…….... [3] [Total: 5] A3 Silver dichromate, Ag2Cr2O7, is a reddish-brown insoluble salt. Silver dichromate can be made by reacting silver nitrate solution with potassium dichromate solution. The equation for the precipitation reaction is shown below. 2AgNO3(aq) + K2Cr2O7(aq) → Ag2Cr2O7(s) + 2KNO3(aq) (a) (i) Deduce the oxidation state of chromium in Ag2Cr2O7. .................... [1] (ii) Write the ionic equation for the formation of silver dichromate. ....................................................................................................................... [1] (b) In a separate experiment, solid silver nitrate and solid potassium dichromate are added to a trough of water, as shown in the set-up below. After five minutes, a reddish-brown solid appeared at the position marked S on Fig. 3.1. Fig. 3.1 solid potassium dichromate water solid silver nitrate plastic trough

5 [Turn over (i) Explain why a reddish-brown solid appeared at the position marked S. ............................................................................................................................ ............................................................................................................................ ....................................................................................................................... [2] (ii) 2 g of solid silver nitrate and 4 g of potassium dichromate were added to the trough of water. Calculate the number of moles of silver nitrate and potassium dichromate used respectively. number of moles of silver nitrate = ……………………… mol number of moles of potassium dichromate = ……………………… mol [3] (iii) Silver nitrate and potassium nitrate solutions are colourless while potassium dichromate solution is orange. Based on your answer in (b)(ii), predict the colour of the solution in the trough after the reaction is complete. Explain your answer. ............................................................................................................................ ............................................................................................................................ ....................................................................................................................... [2] (c) Chromium exists as several naturally -occuring isotopes, including chromium -52 and chromium-54. Complete Table 3.1 to show the number of subatomic particles in these two isotopes of chromium. Table 3.1 chromium-52 chromium-54 number of protons number of neutrons number of electrons [2] [Total: 11]

6 A4 Both hydrazine (represented as N2H4 or H2NNH2) and hydrogen can be used as rocket fuel propellants. Hydrogen undergoes combustion with oxygen to form water only whereas h ydrazine undergoes combustion with oxygen to produce nitrogen and water . Both reactions are exothermic. T