Punggol Prelim P2

EXP PUNGGOL SECONDARY SCHOOL SECONDARY 4 EXPRESS 2024 PRELIMINARY EXAMINATION QUESTION & ANSWER BOOKLET NAME CLASS INDEX NUMBER Chemistry Paper 2 6092 26 August 2024 1 hour 45 minutes READ THESE INSTRUCTIONS FIRST Write your class, register number and name on all the work you hand in. Write in dark blue or black ink 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, highlighters, glue or correction fluid. Section A (70 marks) Answer all questions. Section B (10marks) Answer one question. Write your answers in the spaces provided. A copy of the Periodic Table is printed on page 25. 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. For Examiner’s use Parent’s Signature Section A /70 Section B /10 - - Total /80 This paper consists of 25 printed pages and 1 blank page.

2 Section A Answer all the questions in the spaces provided. 1 The list below shows the chemical formulae of some compounds. NH4Cl Na 2CO3 Ca I2 ZnCl2 CaCl2 V 2O5 PbO Al(NO3)3 SiO 2 (a) State one aqueous substance that produces a white precipitate that is soluble in excess aqueous ammonia. ……………………………………………………………………………………………….. [1] (b) State one substance that reacts with both an acid and an alkali. ……………………………………………………………………………………………….. [1] (c) Contact process is the industrial process used to make sulfuric acid. State one substance that can be used to catalyse contact process. ……………………………………………………………………………………………….. [1] (d) (i) State one substance that reacts with aqueous sodium hydroxide on heating to give a pungent gas that turns moist red litmus paper blue. ……………………………………………………………………………………….. [1] (ii) Write an equation for the reaction in (d)(i). ……………………………………………………………………………………... [1] [Total: 5]

3 2 The composition of three isotopes of an element, G, is shown in the Table 2.1 below. Table 2.1 particle number of protons number of electrons number of neutrons G1 16 16 G2 18 G3 16 G1 is electrically neutral. G2 is negatively charged, with a fully filled valence electron shell. The mass number of G3 is higher than that of G1 by 4. (a) Define isotopes. ………………………………………………………………………………………………. ………………………………………………………………………………………………. [1] (b) (i) Use the information provided to complete Table 2.1. [2] (ii) Determine the nuclide notation of atom G2, showing clearly the chemical symbol found in Periodic Table, mass number and proton number in your answer. ……………………………………………………………………………………… [1] [Total: 4]

4 3 Fig 3.1 shows a set-up for measuring the rates of diffusion of gases at a constant temperature. The rate of diffusion is measured in terms of the time taken for the water level to rise from A to B as the gas diffuses out of the diffusion plug. . Fig 3.1 Table 3.1 shows the results of this experiment. Table 3.1 gases time/s relative molecular mass carbon monoxide, CO 119 chlorine, Cl2 190 methane, CH4 90 oxygen, O2 127 (a) (i) Complete Table 3.1 with the relative molecular mass of the gases. [1] (ii) Peter makes this conclusion: “The time taken for the water level to rise from A to B is directly proportional to the relative molecular mass of each gas.” Do the measurements obtained in the experiment support this conclusion? Explain your reasoning. [2]

5 (b) Jane repeated the experiment with sulfur dioxide gas. She found that the time taken for the water level to rise from A to B is 72 seconds. Using the data in Table 3.1 and relative molecular mass of sulfur dioxide, predict the time taken for the water level to rise from A to B for sulfur dioxide gas. Explain the deviation of the actual time taken from your prediction. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. ……………………………………………………………………………………………….. [2] [Total: 5] 4 Brick-red copper(I) oxide dissolves in dilute sulfuric acid to produce copper(II) sulfate, copper metal and water as shown in the equation below. Cu2O (s) + H2SO4 (aq)  Cu(s) + CuSO4 (aq) + H2O(l) (a) A disproportionation reaction is a redox reaction in which one substance is simultaneously oxidised and reduced. In terms of oxidation states, explain why the reaction between copper(I) oxide and sulfuric acid is a disproportionation reaction. ………………………………………………………………………………………………. ……………………………………………………………………………………………… ………………………………………………………………………………………………. ………………………………………………………………………………………………. ……………………………………………………………………………………………… ……………………………………………………………………………………………… [3]

6 (b) (i) Paramelaconite is a rare, dark coloured oxide of copper that was discovered in Arizona in 1890. Paramelaconite has the following percentage composition by mass: Cu: 84.1% O: 15.9% The relative molecular mass of paramelaconite is 304. Prove that the molecular formula of paramelaconite is Cu4O3. [2] (ii) Paramelaconite reacts with sulfuric acid to undergo a disproportionation reaction. The word equation for the reaction is as shown. paramelaconite + sulfuric acid → copper(I) oxide + copper(II) sulfate + water Complete the balanced equation for the reaction. Cu4O3 + …………………. → ….…………... + ………………… + ……………… [1] [Total: 6]

7 5 Chromium can be used as a protective metal for both steel and pure iron. Stainless steel is an alloy of iron which contains approximately 20% chromium mixed with iron and some small amounts of other metals. Fig 5.1 shows the arrangement of atoms in stainless steel. Fig. 5.1 When chromium metal is added to nitric acid, rapid effervescence is observed. However, effervescence stops after a short while when chromium is added to sulfuric acid. (a) Stainless steel is harder than pure iron. Use ideas about the arrangement of atoms in stainless steel to explain why. ……………………………………………………………………………………………….. ………………………………………………………………………………………………. ………………………………………………………………………………………………. [2] (b) (i) Describe a test for the gas produced when chromium metal is added to nitric acid. State the observation. ……………………………………………………………………………………….. ……………………………………………………………………………………….. [1] (ii) Using information provided on the reaction between chromium and sulfuric acid, predict and explain the solubility of chromium sulfate in water. ……………………………………………………………………………………….. ……………………………………………………………………………………….. ……………………………………………………………………………………….. ……………………………………………………………………………………….. [2]

8 (iii) Using your answer in (b)(ii), describe a method to prepare pure and dry chromium sulfate salt. ……………………………………………………………………………………….. ……………………………………………………………………………………….. ……………………………………………………………………………………….. ……………………………………………………………………………………….. ……………………………………………………………………………………….. [2] (c) The chromium in the stainless steel reacts with oxygen in the air to form chromium(III) oxide. Chromium(III) oxide forms a layer on the surface of the stainless steel. This layer stops the iron in the stainles