SMSS Sec 3 pure chem paper 2 2024

This document consists of 15 printed pages. ST. MARGARET’S SCHOOL (SECONDARY) End-of-Year Examinations 2024 CANDIDATE NAME CLASS REGISTER NUMBER CHEMISTRY Paper 2 Theory Secondary 3 Express 6092/02 26 September 2024 2 hours Additional Materials: NIL READ THESE INSTRUCTIONS FIRST Write your name and register number on all the work you hand in. Write in dark blue or black pen on both sides of the paper. You may use a soft pencil for any diagrams, graphs, tables or rough working. Do not use staples, paper clips, highlighter, glue or correction fluid. Answer all questions in the spaces provided. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. The use of an approved scientific calculator is expected, where appropriate. A copy of the Periodic Table is printed on page 15. For Examiner’s Use Total / 65 marks Paper 1 and 2:

2 SMS(S) 2024 Answer all the questions in this section in the spaces provided. The total mark for this section is 65. 1 Use only the substances below to answer the following questions. Each substance may be used once, more than once, or not at all. (a) Name one substance that has the same rate of diffusion as nitrogen gas. [1] (b) Name one substance which is a neutral oxide. [1] (c) Which two substances react to form a blue solution? [1] (d) Which two elements combine to form a solid that has a high melting point? [1] (e) Which two substances contain atoms arranged in a tetrahedral manner? [1] [Total: 5] lithium sulfuric acid carbon monoxide iodine copper(II) oxide water silicon dioxide methane bromine hydrochloric acid graphite silicon

3 SMS(S) 2024 2 A sample of black ink contains a mixture of red, blue and yellow dyes. A solvent mixture of ethanol and water can be used to separate the dyes in the black ink. The coloured dyes have different Rf values in solvents with different compositions of ethanol as shown in the graph in Fig 2.1. (a) Using information from the graph in Fig 2.1, explain why pure water would not be suitable for the separation of the black ink by using paper chromatography. [2] (b) A student carried out chromatography on the black ink using a certain mixture of ethanol and water as a solvent. The result showed only one spot on the chromatogram. From the graph in Fig 2 , state the percentages of ethanol and water in the solvent which the student used that resulted in only one spot. [1] Fig 2.1

4 SMS(S) 2024 (c) The black ink was separated using 80% of ethanol. What is the distance travelled by a spot of blue dye if the solvent front on the chromatogram is 10.0 cm? Show your working. [2] [Total:5] 3 Uranium exists as isotopes, uranium-235 and uranium-238. The relative abundance of the isotopes are: 0.7% uranium-235 and 99.3% uranium-238. (a) Using your knowledge of Atomic Structure, explain why uranium-235 and uranium-238 are isotopes. State clearly the number of sub- atomic particles to support your answers. [3] (b) Calculate the accurate average atomic mass of Uranium. [2] (c) The radioactive uranium-238 isotope will decay forming thorium-234 isotope and particle X according to the equation below. Use the Periodic Table to identify particle 𝑿𝑏 𝑎 . [1] [Total:6]

5 SMS(S) 2024 4 Oxygen and chlorine combine to form a brownish-yellow gas, dichlorine monoxide (Cl2O). Oxygen and chlorine also combine with aluminium to form aluminium oxide and aluminium chloride respectively. (a) Draw a “dot and cross” diagram to show the bonding in dichlorine monoxide. Show only the valence electrons. [2] (b) Aluminium oxide has a melting point of 2,072 °C while aluminium chloride has a melting point of 192.4 °C. Using your understanding of bonding and structure, indicate with a tick () whether the following statements are true or false. Statements True False (i) The ionic bonding in aluminum oxide is much stronger than in aluminium chloride. (ii) Aluminium chloride has simple molecular structure while aluminium oxide has giant ionic lattice structure. (iii) Both aluminum oxide and aluminium chloride can conduct electricity when molten. [3] [Total:5]

6 SMS(S) 2024 5 Sodium hydride (NaH) is an ionic compound formed between sodium and hydrogen. (a) Draw a dot and cross diagram to show the bonding in sodium hydride. Show all electrons. [2] (b) In a reaction, 0.24 g of sodium hydride was reacted with 1.8 cm3 of water which contained a few drops of Universal Indicator, to form sodium hydroxide solution and hydrogen gas at r.t.p. (i) Write a balanced chemical equation for the above reaction. [1] (ii) State the change in colour of the Universal Indicator in the reaction. [1] (iii) Given the density of water is 1 g/cm3, determine the limiting reactant of this reaction and hence calculate the number of moles of sodium hydroxide formed. [3] [Total:7]

7 SMS(S) 2024 6 (a) Ethanedioic acid is a colourless crystalline solid with the formula H 2C2O4. It is an organic compound with a melting point of 103oC. A student tested the electrical conductivity of his sample of ethanedioic acid and found that the colourless acid crystals did not conduct electricity. However, he found that the aqueous solution of the acid could conduct electricity. Explain why the pure acid does not conduct electricity but can do so when dissolved in water. [2] (b) A pH datalogger measures pH changes during some titration experiments. In Experiment 1 , dilute hydrochloric acid was added from a burette to 20.0 cm3 of 0.200 mol/dm3 aqueous sodium hydroxide. The pH datalogger results are shown in Fig 6.1. Experiment 2 is carried out by titrating ethanedioic acid with a solution of sodium hydroxide of the same concentration and volume as that used in Experiment 1. The pH datalogger results are shown in Fig 6.2. Volume of ethanedioic acid / cm3 Volume of ethanedioic acid/ cm3 Experiment 2 Fig 6.2

8 SMS(S) 2024 (i) Use the information given in Fig 6.1 to calculate the concentration of dilute hydrochloric acid used in Experiment 1. [2] (ii) Sodium ethanedioate solution was obtained in Experiment 2. Use the information in Fig 6.2 to determine the pH of sodium ethanedioate solution. [1] (iii) A list of indicators with the pH range at which it changes colour is given. iIndicators Colour change pH range at which colour change occurs Bromothymol blue Yellow - blue 6.0 - 7.6 Litmus Red - blue 5.0 - 8.0 Methyl orange Red - orange 3.1 - 4.4 Phenolphthalein Colourless - red 8.2 - 9.8 Thymol blue Red - yellow 1.2 - 2.8 Identify two suitable indicators that could be used to determine the end-points of both experiments 1 and 2. [2] [Total: 7]

9 SMS(S) 2024 7 Substance X is a mixture of two solids, V and W. The flowchart below shows some procedures performed on substance X. (a) Outline procedure Y. ]2] (b) Identify substances S, V and W S: ……………………. V:…………………….. W:……………………… [3] (c) Write an ionic equation for the reaction in which substance T was formed. [1]