2021 SNGS Prelim P2

This document consists of 20 printed pages. [Turn over Name: _______________________________ ( ) Class:___________ PRELIMINARY EXAMINATION GENERAL CERTIFICATION OF EDUCATION ORDINARY LEVEL _____________________________________________________________________ CHEMISTRY 6092/02 Paper 2 23 August 2021 1hour 45minutes _____________________________________________________________________ READ THESE INSTRUCTIONS FIRST Write your name, register number, and class clearly in the spaces provided at the top of this page. Write in dark blue or black pen only. You may use a soft pencil for any diagrams or graphs. Do not use highlighters, glue, and correction fluid or correction tape. Section A Answer all questions in the spaces provided. Section B Answer all three questions, the last question is in the form of either/or. Answer all questions in the spaces provided. A copy of Periodic Table is provided on page 2. The number of marks is given in brackets [ ] at the end of each question or part question. The use of a scientific calculator is expected, where appropriate. For Examiner’s Use Section A (50) Section B (30) Total (80)

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3 Section A Answer all the questions in this section in the space provided. The total mark for this section is 50. A1 The following table shows some substances and their properties. substance melting point (oC) boiling point (oC) solubility in water electrical conductivity when solid when liquid A 3550 4830 insoluble poor poor B -114 -85 soluble poor poor C 1538 2862 insoluble good good D 801 1413 soluble poor good E 98 882 soluble good good (a) Explain why (i) B has a low melting point while A has a very high me lting point , in terms of bonding. ……………………………………………………………….....……………… ……………………………………………………………….....……………… ………………………………………………………………………………… …..……………………………………………………………………………… ………………………………………………………………………………..[3] (ii) E, but not D, can conduct electricity at room temperature, in terms of bonding and structure. ……………………………………………………………….....……………… ……………………………………………………………….....……………… ………………………………………………………………………………… …..……………………………………………………………………………… ………………………………………………………………………………..[3] (b) Given that E is an element, suggest a possible identity for E. ………………………………………………………………………………...........[1]

4 (c) C is an element used as a catalyst in the Haber process. State the identity of C. ……………………………………………………………………..........................[1] [Total: 8 marks] A2 Silver dichromate(VI), Ag2Cr2O7, is a red insoluble salt. Silver dichromate (VI) can be made by reacting silver nitrate solution with ammonium dichromate (VI) solution. The chemical equation for the reaction is shown below. 2AgNO3 (aq) + (NH4)2Cr2O7 (aq) → 2NH4NO3 (aq) + Ag2Cr2O7 (s) (a) Describe how you could obtain pure dry silver dichromate (VI) after mixing silver nitrate solution and ammonium dichromate(VI) solution. ……………………………………………………………………………………..… ……………………………………………………………………………………….. …………………………………………………………………………………….[2] (b) Aqueous sodium hydroxide was added to a sample of ammonium dichromate(VI) solution. The mixture was then warmed and damp Unive rsal Indicator paper was held above the mixture. State what would happen to the Universal Indicator paper. …………………………………………………………………………………….[1]

5 (c) The apparatus shown was set up. After five minutes, a red solid appeared along the l ine marked S on the diagram. (i) With the use of an ionic equation, explain how the red solid is formed at S. ……………………………………………………………….....………………. ……………………………………………………………….....………………. ………………………………………………………………………………….. ………………………………………………………………………………….. ……………………………………………………………………................[3] (ii) The experiment was repeated with ammonium chloride in place of ammonium dichromate(VI). Describe and explain the differences in the observation. ………………………………………………………………………………….. …..……………………………………………………………………………… …………..……………………………………………………………………[2] [Total: 8 marks]

6 A3 Hydroxypropanoic acid , also known as lactic acid, is a weak acid produced through anaerobic metabolism. (a) A student claims that pure liquid hydroxypropanoic acid conducts electricity. Do you agree with the student? Explain your answer. …………………………………………………………………………………….[1] (b) Describe what you would observe when Universal Indicator is added to a 0.1mol/dm3 solutions of hydroxypropanoic acid and sulfuric acid respectively. Explain your answer. ……………………………………………………………………………………..… ……………………………………………………………………………………….. ……………………………………………………………………………………….. ………………………………………………………………………………….....[3] (c) A solution containing 0.172 g of hydroxypropanoic acid (HA) is titrated with 0.100 mol/dm3 aqueous sodium hydroxide according to the equation below. HA + NaOH → NaA + H2O The volume of sodium hydroxide solution needed to exactly neutralise the acid is 23.2 cm3. Calculate the relative molecular mass of the hydroxypropanoic acid. [2] [Total: 6 marks]

7 A4 Iron metal can be extracted from its ore using the Blast Furnace. (a) When iron is extracted from haematite in the Blast Furnace, waste gases are formed. Name the waste gases from the Blast Furnace. …………………………………………………………………………………….[1] (b) Can electrolysis of aqueous iron(III) sulfate be used to extract iron? Explain your answer. ……………………………………………………………………………………..… ……………………………………………………………………………………….. …………………………………………………………………………………….[2] (c) Write ionic equations for the reactions at the electrodes for the electrolysis of molten iron(III) oxide. Anode: ………………………………………………………………………… Cathode: …………………………………………………………………………[2] (d) Calculate the mass of iron that can be extracted by the electrolysis of 10 tonnes of molten iron(III) oxide. [1 tonne = 1000 kg] [3] (e) Can aluminium be extracted from its ore, A l2O3, by the blast furnace method? Explain your answer. ……………………………………………………………………………………..… ……………………………………………………………………………………….. …………………………………………………………………………………….[2] [Total: 10 marks]

8 A5 The diagram below shows an experimental set-up of a simple cell and an electrolytic cell. Electrodes A and B are platinum electrodes. (a) Which beaker is the simple cell? Explain your answer. ……………………………………………………………………………………..……. ………………………………………………………………………………………….. ………………………………………………………………………………………..[2] (b) Draw arrows on both wires to show the flow of electrons in the circuit above. [2] (c) Describe what would be observed at electrodes A and B. ……………………………………………………………………………………..……. ………………………………………………………………………………………….. ………………………………………………………………………………………..[2] (d) The experiment is repeated with electrode B in beaker X cha