Name:..Index Number../... 233/2 Candidate s Signature.... CHEMISTRY Paper 2 Date... (THEORY) July/ August 2014 2 hours THE LAMU COUNTY MOCK EXAMINATIONS 2014 Kenya Certificate of Secondary Education CHEMISTRY THEORY Paper 2 2 hours Instructions to Candidates a). Write your name and index number in the spaces provided above b). Sign and write the date of examination in the spaces provided above. c). Answer all the questions in the spaces provided d). KNEC mathematical tables and silent non-programmable electronic calculators may be used. e). All working MUST be clearly shown where necessary f). This paper consists of 16 printed pages. g). Candidates should check the question paper to ascertain that all the pages are printed as indicated and that no questions are missing h). Candidates should answer the questions in English For examiners Use only 1. (a) The equation below represents a redox reaction. Question Score Candidates Score 1 14 2 10 3 14 4 10 5 09 6 11 7 12 Total 80 Cr2O7 2- (aq) + 14H + (aq) + 6Fe 2+ (aq) 2Cr 3+ (aq) + 7H2O(l) + 6Fe 3+ (aq)
(b) (i) Which of the above ion has been I. Oxidized II. Explain Reduced Explain The diagram below shows apparatus used to electrolyze a saturated solution of sodium chloride using carbon electrodes. Y X Saturated solution of sodium chloride (c) (i) Name gas X. (ii) Write an equation for the reaction producing gas Y. (iii) Explain why the electrolyte becomes alkaline after sometimes The table below gives the reduction potentials obtained when half cells for each of the metals represented by the letters JKLMN were connected to a copper half cell as the reference electrode.
Metal J K L M N Reduction Potential (V) - 0.10-0.40-0.00 0.45 1.16 (i) What is metal L likely to be? Explain. (ii) Which of the metals cannot be displaced from the solution of its salts by any other metal? Give a reason. (iii) Calculate the e.m.f. of the electrochemical cell constructed from half cells K and M. (iv) Write the cell representation of the electrochemical cell in (iii) above. (v) Explain the role of a salt bridge. 2. Solubility of potassium nitrate and copper (II) sulphate were determined at different temperatures. The following data was obtained. Temperature 0 20 40 60 80 100 0 C Solubility of KNO3 12 30 75 125 185 250
100g of water CUSO4 15 20 35 45 65 80 (a) On the graph provided plot solubility curves for both salts. (3 marks) (b) Determine from the graph the solubilities of each salt at 50 0 C. I. KNO3 II. CuSO4
III. At what temperature was the solubility of both salts equal? IV. Saturated solution of potassium nitrate at 70 0 C was cooled to 20 0 C. What mass of the crystals will be deposited? (c) (i) Define hard water (ii) Using chemical equations explain 2 methods used to remove temporary hardness of water. 3. a) Study the information given below and answer the questions that follow. Element Atomic radius (nm) Ionic radius (nm) Formula of oxide Melting point of oxide ( C) P Q R S 0.364 0.830 0.592 0.381 0.421 0.711 0.485 0.446 A2O -119 BO2 837 E2O3 G2O5 1466 242
T 0.762 0.676 JO 1054 (i) Which elements are non-metals? Give a reason. (ii) (iii) Explain why the melting point of the oxide of R is higher than that of the oxide of S. Give two elements that would react vigorously with each other. Explain your answer. 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) Ionization Energy_KJ/Mole Element Electronic configuration 1 st 1.E 2 nd 1.E A 2.2 900 1800 B 2.8.2 736 1450 C 2.8.8.2 590 1150 (i) What chemical family do the elements A, B and C belong? (ii) What is meant by the term ionization energy?
(iii) (iv) The 2 nd ionization energy is higher that the 1 st ionization energy of each. Explain When a piece of element C 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) I. State any two factors that would have increased the yield of Sulphur (IV) Oxide. II. Write a balanced equation for the absorption of Sulphur (VI) Oxide. III. State any two important uses of Sulphuric acid. 4. (a) The sketch below represents a graph obtained when zinc granules were reacted with excess 0.2M Sulphuric (VI) acid in the presence of a catalyst in a conical flask placed on an electronic balance. Loss of mass (g) Time(s)
(i) Write an equation for the reaction that took place. (ii) Explain why there is loss in mass. (iii) Name the catalyst used (iv) (a) Sketch, on the same axes, the curves obtained when: I the same mass of zinc powder was used under the same conditions. II no catalyst was used. (1mark) (b) In the contact process, sulphur (IV) oxide is converted to Sulphur (VI) oxide in the catalytic chamber in which a dynamic chemical equilibrium is reached. 2SO2 (g) + O2 (g) 2SO3 (g); H = -97kJmol¹ (i) What is meant by dynamic equilibrium? ii) State and explain how each of the following would affect the position of equilibrium. a) Decrease in temperature. b) Decrease in pressure.
(iii) Equilibrium exists between chromate and dichromate ions as shown below. 2CrO² + 2H + (aq) Cr2 O² + H2O (l) 4(aq) (Yellow) (Orange) State and explain the observation made when aqueous sodium hydroxide is added to the above mixture. 7(aq) 5. (a) (i) In the space provided sketch a labeled diagram to show how hydrogen chloride gas can be prepared and collected in the laboratory using sodium chloride and concentrated sulphuric (VI) acid. (The gas need not be dry)
(ii) Write an equation for the reaction that takes place to generate the Gas. (iii) Name one drying agent for hydrogen chloride gas (iv) State and explain the observations that would be made when Hydrogen chloride as is bubbled through a solution of lead (II) nitrate. (b) (v) Concentrated hydrochloric is used for removing oxides from metal surfaces (pickling). Explain why concentrated nitric (v) acid cannot be used for the purpose. When solid sodium carbonate was added to a solution of hydrogen chloride in methyl benzene, there was no apparent reaction. On addition of water to resulting mixture, there was a vigorous effervescence. Explain these observations. (3 marks)
6. Use the information in the scheme below to answer the questions that follow. P K 2 Cr 2 O 7 Step II Hydrogen gas Step I Butan -1-01 Burn Step III Products Step IV CH 3 CH 2 CH=CH 2 Conc. H 2SO 4 + H 2O Step V Step VI Butan -1-01 Q CH3COOCH2CH2CH2CH3 a) Name substance P b) Give the structure and name of compound Q. c) Write the equation for the chemical reaction in steps III d) Name the reagents and conditions necessary for the reaction in (i) Step IV Reagents
(ii) Conditions (1mark) Step VII Reagents Conditions e) What name is given to the reaction in step VII? f) Below are two reactions showing how a long chained alkanoic acid can be converted into detergent B. I. CH2 C17H35COOH CH C17H35COOH +3H2O CH2 C17H35COOH 3C17H35COOH + C3H8O3 II. 3C17H35COOH + 3NaOH C17H35COONa + 3H2O (Detergent B)
(i) Name the type of reaction in I II (ii) Give one disadvantage of using detergent B in washing clothes. 7. Study the scheme shown below and answer the questions that follow.
a) i) Name ore Q and solid R.
Ore Q Solid R. ii) Explain why step I is necessary iii) Explain happens in step II iv) Why is cryolite added in step III. b) i) Why is the anode replaced from time to time during the electrolysis? ii) iii) During the reaction in step IV Na+ and F- ions are note discharged. Explain. Write ionic equations for the reaction that takes places at the anode and cathode in step IV. At anode At cathode. c) State two reasons why aluminium is preferred to copper in the manufacture of overhead electric cables.
d) Aluminium is high in the reactivity series yet it does not react with water and air. This is the last printed
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