2022 YHSS Chem Prelims P2

1 YUHUA SECONDARY SCHOOL PRELIMINARY EXAMINATION 2022 SECONDARY FOUR EXPRESS CANDIDATE NAME CLASS INDEX NUMBER CHEMISTRY 6092/02 Paper 2 25 August 2022 1 hour 45 minutes Candidates answer on the Question Paper. Setter: Ms Cerenna Ng No Additional Materials are required. READ THESE INSTRUCTIONS FIRST Write your name, class and index number on all the work you hand in. Write in dark blue and black pen. You may use a pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Section A Answer all questions in the spaces provided. Section B Answer all three questions, the last question is in the form either/or. 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. A copy of the Periodic Table is printed on page 21. The use of an approved scientific calculator is expected, where appropriate. For Examiner’s Use Section A / 50 Section B / 30 Total / 80 This document consists of 21 printed pages, inclusive of this page. [Turn over

2 YHSS/Prelims/2022 Secondary Four Express Chemistry (Paper 2) Section A (50 marks) Answer all the questions in the spaces provided. 1 Deuterium is an isotope of hydrogen. The diagram shows the structure of an ion of deuterium. (a) Complete the following table to show the names and charges of the particles in this deuterium ion. symbol name charge neutron +1 −1 [1] (b) Using the symbol D to represent deuterium, give the chemical formula of (i) the ion shown above; .…......... [1] (ii) the compound formed between deuterium and sodium. .…......... [1] (c) Would you expect the oxide of deuterium to be a solid, a liquid or a gas at room temperature and pressure? Explain your reasoning. ………….…………….…………………………………….……………………………………….. ………….……………………………………………….……………………………………….. [2] [Total: 5] - - + + -

3 YHSS/Prelims/2022 Secondary Four Express Chemistry (Paper 2) [Turn Over 2 Two samples of rocks, X and Y, were tested to find out if they originated from the same region. The rock samples were crushed and a suitable acid was added to dissolve impurities in the rock samples. The resulting solutions from the mixtures were chromatographed, together with five known metal ions. The diagram shows the chromatograms after spraying with a locating agent. (a) State why a locating agent was used. …………….…………….……………………..…………….……………………………………… …………...…………………………………..………….………………………………………..[1] (b) Deduce if the two samples of rock were from the same region. Give a reason for your answer. …………….…………….……………………..…………….……………………………………… …………….…………….……………………..…………….……………………………………… …………….…………….……………………..…………….……………………………………… …………….…………….……………………..…………….……………………………………… …………...…………………………………..………….………………………………………..[2] metal ion solutions rock X rock Y solvent front start line

4 YHSS/Prelims/2022 Secondary Four Express Chemistry (Paper 2) (c) Calculate the Rf value for Pb2+ ions. [1] (d) Draw on the diagram, the spot for Zn2+ ions given that the Rf value for these ions is 0.75. [1] [Total: 5]

5 YHSS/Prelims/2022 Secondary Four Express Chemistry (Paper 2) [Turn Over 3 Substance Z is a mixture of a compound and an element. The compound is soluble in water but the element is not soluble in water. The diagram shows the results of a series of qualitative analysis tests on substance Z. (a) Name the following substances. (i) yellow precipitate, P ………………………………………......... [1] (ii) white precipitate, Q ………………………………………......... [1] (iii) white precipitate, S ………………………………………......... [1] (iv) colourless gas, T ………………………………………......... [1] (b) Identify the cation present in the colourless solution R. …………...…………………………………..………….………………………………………..[1] (c) Construct a balanced chemical equation for the reaction of the grey residue from the filtration with warm hydrochloric acid. …………...…………………………………..………….………………………………………..[1] [Total: 6] warm HCl aqueous NH3 white precipitate S; soluble in excess aqueous ammonia colourless solution R colourless gas T; burns with a ‘pop’ sound dilute NaOH white precipitate Q; insoluble in excess sodium hydroxide solution dilute HNO3 and aqueous AgNO3 yellow precipitate P filtrate: colourless solution grey residue shake with excess water; filter substance Z

6 YHSS/Prelims/2022 Secondary Four Express Chemistry (Paper 2) 4 A student performed an experiment using the apparatus shown below. Syringe 1 contains 90 cm3 of air. The air is forced over heated magnesium into syringe 2. The air is then forced back over the heated magnesium into syringe 1. The process is repeated several times until the volume of gas forced back into syringe 1 is constant. The apparatus is allowed to cool to room temperature. The diagram below shows the volume of gas in syringe 1 at the end of the experiment. (a) Construct a balanced chemical equation, including state symbols, for the above reaction. …………….…………………………………………….………………..………………………..[1] (b) Name the major component of the gas remaining in syringe 1. …………….…………………………………………….………………..………………………..[1] (c) The magnesium used for the above reaction was in excess. Calculate the mass of magnesium that has reacted. mass of magnesium = ……………….. g [3] [Total: 5] heat 1 2 1 magnesium

7 YHSS/Prelims/2022 Secondary Four Express Chemistry (Paper 2) [Turn Over 5 Element X exists as a diatomic molecule at room temperature and pressure. An atom of element X has 7 electrons in its second electron shell, which is also its valence shell. Element X undergoes reactions with carbon and calcium to form CX4 and CaX2 respectively. In both of the reactions, X2 has been reduced. A schematic diagram of the reactions is shown below. Reaction with C Reaction with Ca CX4 X2 CaX2 (a) Explain, in terms of oxidation states, why X2 is reduced in both reactions. …………….…………….……………………..…………….……………………………………… …………...…………………………………..………….………………………………………..[1] (b) (i) Identify the type of bonding structure present in CX4 and CaX2. CX4 : ……….….………………………………….…………….…………………….……..[1] CaX2 : ……….…...……………………………….………………….……...……….……..[1] (ii) Draw a ‘dot-and-cross’ diagram to show the arrangement of valence electrons in CaX2. [2] (c) Deduce which product, CX4 or CaX2, has a higher melting and boiling point. Explain your answer in terms of structure and bonding. …………….…………….……………………..…………….……………………………………… …………….…………….……………………..…………….……………………………………… …………….…………….……………………..…………….……………………………………… …………...…………………………………..………….………………………………………..[2] [Total: 7]

8 YHSS/Prelims/2022 Secondary Four Express Chemistry (Paper 2) 6 When iron is heated with steam in a sealed container, an equilibrium mixture is obtained. 3Fe (s) + 4H2O (g) ⇋ 4H2 (g) + Fe3O4 (s) DH = +35 kJ/mol The forward reaction is endothermic. (a) Define the term endothermic. …………….…………….……………………..…………….……………………………………… …………...…………………………………..………….………………………………………..[1] (b) State and explain what happens to the rate of the forward reaction when the temperature is increased and pressure remains constant. …………….…………….……………………..…………….……………………………………… …………….…………….……………………..…………….……………………………………… …………….…………….……………………..…………….……………………………………… …………...…………………………………..………….………………………………………..[2] (c) When the pressure of a reversi