INSTRUCTIONS TO CANDIDATES

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1 NAME. INDEX No.. ADM. NO. CANDIDATE S SIGNATURE 233/2 Date: 30 th July 2013 CHEMISTRY Time: p.m. Paper 2 (Theory) Time: 2 Hours JULY/AUGUST RABAI DISTRICT MOCK EXAMINATION Kenya Certificate of Secondary Education (KCSE) INSTRUCTIONS TO CANDIDATES 1. Write your name and index numbers in the spaces above. 2. Answer all the questions in the spaces provided. 3. Mathematics tables and electronic calculators may be used. 4. All working must be clearly shown where necessary. 5. This paper consists of 18 printed pages. Candidates should confirm this. FOR EXAMINER s USE ONLY Questions Maximum score Candidate s score Total score 80 This paper consists of 16 printed pages. Candidates should check the question paper to ensure that all pages are printed as indicated and no questions are missing. 1

2 1. The grid below is part of the periodic table. Letters do not represent the actual symbols of the elements. Use the table to answer the questions that follow. T S W R K Q N a) Which is the most reactive i. Non- metal? explain (1½mks) ii. Metal? explain (1½ mks) b) Name the chemical family to which elements T and Q belong. c) Write the formula of the compound found when W reacts with S. d) Name the type of bond formed when R and K react. 2

3 e) Explain why element N forms very few compounds if any. (1mk) f) Compare the atomic radii of T and Q. explain. (2mks) g) The table below gives properties of some elements in period three. Chloride M.P ( 0 C) B.P ( 0 C) State at room temp. Structure Bonding NaCl Solid Giant ionic Ionic AlCl (i) Solid Molecular Covalent PCl Solid Molecular (ii) SCl (iii) (iv) Covalent i. Complete the table by filling in the blank spaces (i) and (iv). ( 2mks) ii. Suggest the likely ph of a solution formed when AlCl 3 is dissolved in water. Explain your answer. (2 mks) 2. a) The set up below was used by a student during electrolysis experiment of concentrated copper (II) Chloride solution. Study it and answer the questions that follow 3

4 Test Tube R Concentrated Copper (II) Chloride Electrode Q Platinum Electrode P Battery i. State and explain the change that would be observed in the electrolyte as the experiment progresses. (2mks) ii. After some time test tube R was found to contain a mixture of two gaseous. Name two gases and explain the observations. (2 mks) iii. Which of the electrodes is the anode? Explain your answer. (2mks) iv. In a second experiment, copper electrodes were used with the same electrolyte. A current of 2 amperes was passes for 5 hours through the cell. Determine the change in mass of the anode at the end of the experiment. (Cu = 63.5, I Faraday = coulombs) (3 mks) 4

5 b) The table below gives the standard electrode potential for the metals represented by the letters A, B, C,D and E. study it and answer the questions that follow. Metal Standard Electrode Potential E ø (V) A B C D E i. Calculate the e.m.f of the electrochemical cell represented below. ( 2mks) B (s) / B 2+ (aq)//c 2+ (aq)/c (s) ii. Arrange the metals in a descending order of reactivity. iii. Which metal can be displaced from its solution by all other metals in the table? Explain 5

6 3. a) A hydrocarbon has the general formula C n H 2n-2. Name the homologous series to which it belongs. b) Study the reaction scheme below and answer the questions that follow. H 2 SO 4 (l) Step I Colourless gas Q Ethanol Step III HCl Step II Product U Ethane Step IV U.V light Excess chlorine Product S i. Draw the structural formula of gas Q. ii. Name the type of reaction in steps. I II III.. 6

7 iii. Write a chemical equation for the reaction in step III. iv. Give the IUPAC name of compound S. v. The empirical formula of hydrocarbon is C 2 H 3. The hydrocarbon has a relative molecular mass of 54. Determine its molecular formula. (C = 12, H = 1.0) (2 mks) vi. Draw two different structural formula of the hydrocarbon in (v) above. (2 mks) 4. A student carried out an experiment to determine the molar enthalpy of neutralization of sodium hydroxide by 2M hydrochloric acid. 25 cm 3 of the acid was placed in a beaker and the initial temperature of the solution measured and recorded. 5 cm 3 of sodium hydroxide was added to the beaker and the mixture temperature recorded. The procedure was repeated and the temperature recorded in the table below. Volume of acid (cm 3 )

8 Volume of NaOH added (cm 3 ) Temp ( 0 C) of solution a) On the grid provided plot a graph of temperature against volume of Sodium hydroxide added. (3 mks) b) From the graph, determine i. The maximum expected temperature change T. ii. The volume of sodium hydroxide required to neutralize the hydrochloric acid. (1mk) c) Calculate the heat change that occurred during the reaction (take specific heat capacity of solution to be 4.2 j/kg K, density of solution 1g/cm 3 ). (2 mks) d) Find the number of moles of sodium hydroxide that reacted. 8

9 e) Determine the molar enthalpy of neutralization for this reaction. f) Suggest a reason why the above value in (e) could be lower than the actual value. g) Represent the neutralization reaction in an energy level diagram. (2 mks) 5. a) Sulphur is mined using the frasch process which uses super heated water at C and hot compressed air. i. Explain how water at C is obtained. ii. What is the role of super heated water? 9

10 iii. State the role of compressed air. b) Give two large scale uses of Sulphur. c) In a experiment 3.6g of Sulphur were obtained by reacting hydrogen Sulphide and Sulphur (IV) oxide as shown in the equation below. 2H 2 S (g) + SO 2(g) 2H 2 O (g) + 3S (s) Given that the yield of Sulphur is 75%. Calculate the volume of Sulphur (IV) oxide used at room temperature and pressure. (H=1, S = 32.0, O = Molar gas volume at s.t.p is 24 dm 3 ). (3 mks) d) Study the flow chart below and answer the questions that follow. Air Solid A SO 2(g) Clean Purifier Air SO 2(g) Water Solution L Air Excess NaOH Solution M 10

11 White Precipitate Barium Nitrate i. Other than Sulphur, name the possible identiy of solid A. ii. Write an ionic equation for the formation of the white precipitate. iii. State and explain the observations made when red and blue litmus papers were dropped into solution L. (2 mks) iv. State and explain the observations made when dilute hydrochloric acid is mixed with the white precipitate. (2 mks) 6. a) Magnetic is one of the most abundant use of iron, write its formula. 11

12 b) The flow chart below shows a sequence of reaction starting with iron metal. Study it and answer the questions that follow. Iron metal Step I Step 2 Iron (II) Sulphide HCl (aq) Iron (III) Chloride solution + gas R Step 3 Step 6 1. Oxygen 1. Addition of reagent Q 2. heat Water vapor 2. Filtration Solid P Step 5 Heat Dilute Step 7 Step 4 Iron (III) hydroxide HNO 3 Iron (II) nitrate Dilute HNO 3 solution 12

13 i. Identify the reagent required in step 1 and the condition necessary for the reaction to take place. (2 mks) ii. Identify Gas R Reagent Q Solid P iii. Write an equation for the reaction that takes place in step 5. (1mk) iv. State the observation made in step 4 and step 7 Step 4. (1mk) Step The table below shows two brands of bottled water for drinking and the concentration of different minerals ions in each brand. Study it and answer the questions that follow. Composition in mg/litre Mineral ion KERINGET PUR AQUA Sodium Calcium Magnesium Chloride

14 Nitrate Sulphate Iron fluoride i. Which brand of water contains more hardness? Explain. (2 mks) ii. State the benefits of having the following ions in water. Calcium ions (1mk) Fluoride ions iii. State the disadvantages of having more fluoride ion in dirking water as in the Kenget brand. iv. Both brands of water are heated with ozone, a reactive form of oxygen, before being bottled. Explain why. v. Tap water is usually treated before being used. State what is added to tap water to perform the same function as ozone in (IV) above. 14

15 vi. State the type of water hardness found in two brands of bottled water. vii. Give one method that can be used to remove the type of hardness in (VI) above any water sample. 15

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