BORABU-MASABA DISTRICTS JOINT EVALUATION TEST 2012 Kenya Certificate of Secondary Education (K.C.S.E)

Transcription

1 Name. School Candidate s Signature. Index No /. Date. 233/2 CHEMISTRY Paper 2 (Theory) JULY / AUGUST Time: 2 Hours BORABU-MASABA DISTRICTS JOINT EVALUATION TEST 2012 Kenya Certificate of Secondary Education (K.C.S.E) 233/2 CHEMISTRY Paper 2 (Theory) JULY / AUGUST Hours 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 14 printed pages. Candidates should confirm this. FOR EXAMINER S USE ONLY QUESTION MAXIMUM SCORE CANDIDATE S SCORE Total Score 80 1

2 This paper consists of 14 printed pages. Candidates should check the question paper to ensure that all pages are printed as indicated 1. A student set up the apparatus shown below to prepare and collect dry carbon (IV) oxide gas. State a correction for three mistakes in the set up above. (3 mks) (i) (ii) (iii) (b) 30cm 3 of carbon (II) oxide gas were reacted with 10cm3 of oxygen gas. The resulting mixture of gases was bubbled through an alkali. Determine the volume of the residual gas. (3 mks) 2

3 (c) The flow chart below is for the manufacture of Sodium Carbonate by the Sowely process. Use it to answer the questions that follow (i) Name substance N. (1 mk) (ii) Explain the use of water in chamber B. (1 mk) (iii) Name the two raw materials required in the manufacture of Sodium Carbonate. (1 mk) 3

4 (iv) Write an equation for the reaction taking place in chamber C. (1 mk) 2. The diagram below represents a set up that was used for electrolysis of (a) Aqueous copper (II) nitrate. A gas that relights a glowing splint was produced at electrode A. (i) State the observation made on the electrolyte after the experiment. (1 mk) (ii) Explain how the identity of the product at the Cathode of this electrolysis can be confirmed. (2 mks) 4

5 (iii) State one use of the process illustrated in 2 (a) above. (1 mk) b) The following are standard electrode potentials for some electrodes. The letters do not represent the actual symbols of the elements. Element E θ Volts A 2+ (aq) + 2 e- A (s) A 2+ (aq) + 2 e- B (s) A 2+ (aq) + 2 e- C (s) 0.00 A 2+ (aq) + 2 e- D (s) A 2+ (aq) + 2 e- E (s) (i) Which is the weakest reducing agent? Explain. (1 mk) (ii) Calculate the e.m.f of the cell obtained by combining the half cells of B and D. (2 mks) 5

6 (iii) Write the cell representation for the electrochemical cell obtained in 2 b (ii) above. (1 mk) (iv) Is it possible to store E nitrate in a container made of A. Give a reason for your answer. (2 mks) (c) An element X forms a stable ion X g of element X was electrolyzed completely by passing a current of 1.34 A for 150 minutes. Calculate the Relative Atomic Mass (RAM) of X. (3 mks) 3. Study the table below and answer the questions that follow. Element A B C D E F G Atomic radius (nm) Ionic radius (nm) st Ionization energy KJ/mol Mpt ( o C) Atomic number I Explain why (i) A has a larger atomic radius than its ionic radius? (1 mk) (ii) G has a smaller atomic radius than its ionic radius? (1 mk) II Comment on the trend of melting points from A to C. Explain. (1 ½ mks) 6

7 III What is the general trend of the 1 st ionization energies for elements A F. Explain? (1 mk) IV Explain why D has the highest melting point. (1 mk) (b) The grid below is a section of the periodic table. The letters do not represent the actual symbols of the elements. Use it to answer the questions that follow. Q Y M N K L S O R P (i) How does electro negativity vary from N to P? Explain (2 mks) (ii) Give the formula of the compound formed between L and P. (1 mk) 7

8 ii) An oxide of Y was dissolved in water to form a solution. How would you distinguish between this solution and a solution made by dissolving an oxide of S in water. Explain. (2 mks) 4. (a) Use the bond energies given in the table below to calculate the enthalpy change for the reaction. (3 mks) C 2 H 6 (g) + Br 2 (g) C 2 H 5 Br (g) + HBr (g) Bond C - H C - Br Br - Br H - Br Bond energy (KJMol b) Hydrogen peroxide decomposes according to the equation given below. H 2 O 2 (l) H 2 O (l) + ½ O 2 (g) H = 98 KJMol 6.8g of hydrogen peroxide contained in 75 cm3 of solution with water were completely decomposed. Determine the rise in temperature due to the reaction. Specific heat capacity of water = 4.2 Jg -1 K -1 Density of water = 1gcm -3, O=16.0 and H = 1.0). (3 mks) 8

9 (c) The boiling point of water is C and its melting point is 0 0 C. On the space provided below, sketch the cooling curve that would be obtained when a boiling tube containing water at 90 0 C is immersed in a freezing mixture maintained at C. (3 mks) (d) (i) What is a fuel? (1 mk) (ii) Methane has a higher heating value than butane yet butane is preferred to methane as domestic fuel. Give a reason for this. (1 mk) 5. Use the flow chart below to answer the questions that follow. 9

10 (a) Name the following (i) Gas S (1 mk) (ii) Gas p (1 mk) 10

11 (iii) J (1 mk) (b) Name process in (i) Step I (1 mk) (ii) Step II (1 mk) (iii) Step III (1 mk) (c) Draw two structural Isomers of compound L. (2 mks) (d) Write a chemical equation for the complete combustion of Substance M. (1 mk) (e) Name the reagent and condition in step III. (i) Reagent. (1 mk) (ii) Condition (f) Calculate the mass of salt R that would be formed by using 21.9 tonnes of N when it reacts with excess Sodium hydroxide. (C=12.0, H=1.0, Na=23.0, O=16.0) 11 (2 mks)

12 6. The chief ore of aluminium is bauxite which contains mainly Al 2 O 3.2H 2 O. The ore is initially purified before extraction. (a) Identify the main impurities associated with this ore. (1 mk) (b) Sodium hydroxide solution is used in purifying process. (i) State the condition necessary for this stage. (1 mk) (ii) What is the role of Sodium hydroxide solution? (1 mk) (c) Give an equation for the reaction that form aluminium from aluminium hydroxide. (1 mk) (d) Aluminium is extracted from alumina by electrolysis. (i) In this process, molten cryolite is added to alumina in an electrolysis cell. Explain the role of cryolite. (2 mks) (ii) Write an equation for the reaction that produces aluminium in the electrolytic cell. (1 mk) 12

13 (e) 1 gram of an alloy of copper and aluminium is reacted with dilute hydrochloric acid at s.t.p. The volume of the gas collected was found to be 840cm3. Molar gas volume = 22.4 litres at s.t.p (i) Write the equation for the formation of the gas. (1 mk) (ii) Calculate the amount of copper in the alloy. (3 mks) (Cu = 64 Al=27.0) 7. (a) The scheme below shows various reactions starting with hydrogen and nitrogen. Study it and answer the questions that follow. 13

14 (i) Name the catalyst used in step II (1 mk) (ii) Name substances (2 mks) P Q (iii) Why is concentrated nitric (V) acid transported in aluminium containers and not Copper containers? (2 mks) (iv) The nitric (V) acid produced by this process is 35% pure. Explain how concentration can be increased. 14 (1 mk)

15 (b) An experiment was performed to determine the solubility of Ammonia Chloride in Mol/litre at different temperatures ( 0 C). The table below shows the relationship between solubility and Temperature. Temperature ( o C) Solubility (Mol/ litre (i) Plot a graph of solubility in Mol / litre against temperature ( 0 C). (3 mks) 15

16 (ii) Use the graph to determine the solubility of ammonia Chloride in g/100g of water at 60 0 C. (2 mks END 16