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Name……………………………………………..……… Index No. …………………………..….. School …………………………………………………… Signature of candidate……….……….... Date: …………………………………….. 233/ 2 CHEMISTRY Paper 2 (THEORY) July/Aug. 2008 Time: 2 Hours SIAYA DISTRICT SECONDARY SCHOOLS EVALUATION EXAMINATIONS - 2008 Kenya Certificate of Secondary Education (K.C.S.E) 233/ 2 CHEMISTRY Paper 2 (THEORY) July/Aug. 2008 Time: 2 Hours INSTRUCTIONS TO CANDIDATES Write your name, index number and the name of your school in the spaces provided above. Answer ALL the questions in the spaces provided Mathematical tables and Electronic calculators may be used All working be shown where necessary. FOR EXAMINER’S USE ONLY Question Maximum score Candidates score 1 12 2 12 3 12 4 09 5 13 6 13 7 09 Total Score 80 This paper consists of 12 printed pages. Candidates should check the question paper to ensure that all pages are printed as indicated and no question are missing © The Siaya District Examination Panel Chemistry 233/2 1 Turn Over 1. a) Element Study the information given below and answer the questions that follow. Atomic radius (nm) Ionic radius Formula of oxide Melting point of oxide ( 0 C) A 0.364 0.421 A2O -119 B 0.830 0.711 BO2 837 E 0.592 0.485 E2O3 1466 G 0.381 0.446 G2O5 242 J 0.762 0.676 JO 1054 (i) Which elements are non-metals? Give a reason. (2 marks) (ii) Explain why the melting point of the oxide of E is higher than that of the oxide of G (2 marks) (iii) Give two elements that would react vigorously with each other. Explain your answer. (2 marks) b) Study the information in the table below and answer the questions that follow (The letters do not represent the actual symbols of the elements) Ionisation Energy KJ/Mole Element Electronic configuration 1st 1. E 2nd 1.E X 2.2 900 1800 Y 2.8.2 736 1450 Z 2.8.8.2 590 1150 (i) What chemical family do the elements X, Y, Z belong? (1 mark) (ii) What is meant by ionization energy? (1 mark) (iii) The 2nd ionization energy is higher that the 1st ionization energy of each. Explain(1 mark) (iv) When a piece of element Z is placed in cold water, it sinks to the bottom and an effervescence of a colourless gas that burns explosively is produced. Use a simple diagram to illustrate how this gas can be collected during this experiment. (3 marks) 2. Study the reaction scheme below starting with ethanol and answer the questions that follow. CH3 C2 HOH Step I CH2 = CH2 Step II Conc H2SO4 (1800C Ni catalyst + H2 Step III C B Step IV Conc. H2 SO4 + Water M H H C C H H H2O D Step V Ethanoic acid n E CH3 C-OOC2 HCH3 a) Write down the formula of compound B, C and D b) Name the type of reaction represented by: Step I: Step II: Step IV: Step V: c) (i) To what class of compounds does E and M belong? E: © The Siaya District Examination Panel Chemistry 233/2 2 (3 marks) (1 mark) Turn Over M: (ii) Name the substance E. (1 mark) d) Write the equation of the complete combustion of ethanol (1 mark) e) If the relative molecular mass of M is 47,600; determine the value of n. (C = 12.0 , H = 1.0) (2 marks) f) Using a chemical test, state how you can distinguish between CH2 = CH2 and CH3CH3 (2 marks) 3. An experiment was carried out using magnesium ribbon and dilute hydrochloric acid of different concentrations. The time needed to produce 50cm3 of the gas for every experiment was recorded in the table below: Concentration 2.0 1.75 1.50 1.25 1.00 0.75 0.50 0.25 Of HCL (moles/litre) Time in Seconds (s) 8.8 10.0 11.7 14.0 17.5 18.7 35.0 70.0 I timesec 1 a) Complete the table above for I b) Plot a graph of rate i.e. I timesec 1 timesec 1 (2 marks) against concentration (4 marks) c) From your graph, determine the concentration needed to produce 50cm3 of hydrogen gas when time is 15.0 seconds (2 marks) d) Neutralisation is a method of preparing salts. (i) What is meant by neutralisation? (1 mark) (ii)Describe how you would prepare crystals of sodium nitrate starting with 200cm3 of 2M Sodium hydroxide solution. (3 marks) 4. The table below shows the decay of phosphorous -32 with half life of 14.3 days. Time (days) Mass (g) Radioactivity (counts per min) 0 200 400 14.3 (1st half life) 28.6 (2nd half life) 100 42.9 (3rd half life) 25 57.2 (4th half life) a) (i) Complete the table above (3 marks) (ii) How long would it take for the mass of phosphorous to: i) ¼ of its original mass (1 mark) ii) 1 of its original mass 16 (1 mark) b) In an artificial process of nuclide may be made to disintegrate as shown below: 235 1 230 4 1 92 U + 0 X 90 Th 2 + Y + 2 0X + Z (i) X and Y are not the actual symbols of the particles involved. Use the properties given to identify the particles X and Y. X: ( ½ mark) Y: ( ½ mark) (ii) Identify Z (1 mark) c) Give two applications of radioactivity in industries (2 marks) 5 a) The set up below was used during the electrolysis of 6M hydrochloric acid using inert electrodes. Electrode B Electrode A 6M hydrochloric acid (i) Identify the anions and cations present in the solution. Anions: Cations: (ii) Give a reason why a mixture of gases are obtained at electrode B. © The Siaya District Examination Panel Chemistry 233/2 3 (1 mark) (1 mark) Turn Over Explain your answer (3 marks) (iii) During the electrolysis, a current of 2 amperes was passed through the solution for 3 hours, 20 minutes. Calculate the volume of the gas produced at electrode A (1 Faraday = 96500 Coulombs and molar gas volume at room temperature is 24000 cm3) (3 marks) b) Name two applications of electrolysis (2 marks) c) Use the information below on standard electrode potentials to answer the questions that follow: E volts Cu2+ + 2eCu + 0.34 2+ Fe + 2e Fe - 0.44 + Na + e Na - 2.92 Mg2+ + 2eMg - 2.71 2+ Pb + 2e Pb - 0.14 ½ F2 + eF+ 2.87 ½ Br2 + e Br + 1.09 H+ + e½ H2 0.00 i) From the list select: I. The strongest reducing agent. Give a reason (1 mark) II. The strongest oxidizing agent. Give a reason (1 mark) ii) Calculate the e.m.f. of the cell constructed in (i) above (1 mark) 6. Study the scheme shown below and answer the questions that follow. Ore Q Step I Excess N aoH (aq) Resi due Solution containing Solution containing (Al(O H) 4 ) (Al(OH)4 Spri nkl ing of Sprinkling of AL2O3 and CO2 Al O 3 and CO 2 2 Solid R St ep II Solid Aluminiun Oxide Cryolite Cryolite Na AlF Na 3Alf6 Step III Molten Mixture 3 Step IV 6 Mol ten Aluminiun Step V Uses of al uminium Duralamin alloy for aircraft parts and window frames. Aluminium foil for lini ng food packetts a) (i) Name ore Q and solid R Ore Q (1 mark) Solid R (1 mark) (ii) Explain why step I is necessary (1 mark) (iii) What happens in step II (1 mark) (iv) Why is cryolite added in step III. (1 mark) b) (i) Why is the anode replaced from time to time during the electrolysis? (1 mark) + (ii) During the reaction in step IV Na and F ions are not discharged. Explain (2 marks) (iii) Write ionic equations for the reaction that takes place at the anode and cathode in step IV. At anode (1 mark) At cathode (1 mark) © The Siaya District Examination Panel Chemistry 233/2 4 Turn Over c) State two reasons why aluminium is preferred to copper in the manufacture of overhead electric cables (2 marks) d) Aluminium is high in the reactivity series yet it does not react with water and air. Explain. (1 mark) 7. The flow diagram below represents how hydrogen sulphide can be used to prepare sulphuric acid. Study it and answer the questions that follow. AIR Dry hydrogen sulphide gas Liquid T BURNERS SO3 (g) Gas K CHAMBER Q TOWER Solid x OLEUM a) Name: (i) Gas K: ( ½ mark) (ii) Liquid T: ( ½ mark) ………………………………………………………………………………………………………. b) (i) What is the function of solid X in chamber Q? (1 mark) (ii) Write an equation for the reaction in chamber Q (1 mark) c) State and explain what would be observed if hydrogen sulphide gas is bubbled through: (i) Aqueous copper (II) nitrate solution? (2 marks) d) Write an ionic equation for the confirmatory test for hydrogen sulphide gas. (1 mark) e) Write a chemical equation for the formation of concentrated Sulphuric (VI) acid from the oleum. (1 mark) © The Siaya District Examination Panel Chemistry 233/2 5 Turn Over