BUSIA SUB-COUNTY JET 2016

Transcription

1 Name Index No.. School /2 CHEMISTRY THEORY Paper 2 Time: 2 Hours BUSIA SUB-COUNTY JET 2016 Kenya Certificate of Secondary Education (K.C.S.E) INSTRUCTIONS TO CANDIDATES. Answer all the questions in the spaces provided Mathematical tables and Electronic calculators may be used. All working must be clearly shown where necessary For Examiner s Use only Question Maximum Score Candidates Score Total 80 This paper consists of 11 printed pages. Candidates should check the question paper to ensure that all pages are printed as indicated and no questions are missing

2 1. Use the grid below to answer the questions that follow. Letters do not represent the actual symbol of the elements. 2 F I M O G J K L N P H Q a) What family name is given to elements G and H?. b) State and explain the difference in reactivity between i) G and J ii) N and P c) How does atomic radius of K compare to that of L? Explain.. d) Element R forms an oxide of the formula RO2 and belong to period 2. Indicate in the grid the position of R. e) Explain the trend in melting points in the group of elements to which I and J belong.

3 3 f) Write down the formula of the compound formed between K and P. g) Name the type of bond formed when F reacts with O. Explain... h) Give one use of element Q. i) Write down the electronic arrangement of an ion of H.. N.. 2. The diagram below represents the blast furnace used for the extraction of iron. Study it and answer the questions that follow A (a) (i) At what point X,Y,Z would you expect the highest temperature?.

4 4 (ii) Name two constituents of A (iii) What is the main use of the constituents of A in this process? (iv) What is the role of the hot blasts in this process? (v) Why is it possible to separate iron from the slag? (vi) Write an equation for the reaction that take place to produce iron. (vii) Explain why the iron produced in the blast furnace has to be given further treatment before use in building bridges. (b) (i) What is meant by galvanization iron? (ii) Why is it necessary to galvanize iron?

5 5 (c) Study the chart below and answer the questions that follow Iron H2O NaOH(aq) HCl(g) Solid Y Aqueous Y Green ppt Heat Water HCl(g) KMnO4 Gas W Iron Heat H2O NaOH(aq) Solid Z Aqueous Z Brown ppt (i) Name W,Y and Z (3 marks) (ii) Write an ionic equation for the formation of the brown precipitate 3. (a) Use the table below to answer the questions that follow. Substance A B C D E Symbol R COO - Na + R-COOCH2 R-COO-CH R-COO-CH2 R-OSO3 - Na + CH2OH CHOH CH2OH [-CH2-CH2.]n (i) Which substance is I a soapless detergent II soapy detergent III an ester IV a triol V polymer (ii) Which substance forms a scum when used with hard water? (2 ½ marks) (½ marks)

6 (b) Study the reaction mechanism below and use it to answer the questions that follow. 6 (i) Name substances K. L (ii) What observations would be made if L is passed through acetified potassium permanganate solution? (iii) Name the first member of the family whose C3H4 belong (iv) Identify the reagents used at stages: I II III IV (v) Name the reaction taking place at I II III IV

7 7 c) The structure below is for polyphenyl ethane. Benzene ring (i) Write down the structural formula of phenylethene. (ii) Determine the number of monomers making the above compound if its relative molecular mass is 104,000. The benzene ring has six carbon and five hydrogen atoms. (C=12, H=1) (iii) Give one property of the above compound that making it be used as an insulation material. 4. The table below shows the temperature when 5cm 3 of 1. 25M HCI was added to 50cm 3 NaOH solution at a time. Volume of 0.25M HCl added Temperature of solid C

8 8 (a)plot a graph of temperature against volume of 1.25MHC1 added (4 marks)

9 9 b) From the graph determine the change in temperature (i) Determine the volume of 1.25MHCl needed to neutralize 50 cm 3 of NaOH. (c) Determine the concentration of NaOH in moles per litre. (3 marks) 5. The standard electrode potential of some half cells (in volts)are given below. (i) Zn 2+ (aq) + 2e Zn(s) (ii) Cr 3+ (aq) +3e Cr(s) (iii) Sn 2+ (aq) +2e Sn(s) (iv)2b + (aq) +2e B (v) Cu 2+ (aq) +2e Cu(s) (vi) Fe 3+ (aq) +2e Fe 2+ (aq) (vii)br2(aq) +2e 2Br a) Which element is represented by letter B? Explain. b) Identify the strongest reducing agent and strongest oxidizing agent. (i) Strongest reducing agent (ii) Strongest oxidizing agent

10 10 c) Write the equation and calculate the e.m.f of the electrochemical cell constructed from half cells in b(i) and (ii) above. d) Write the cell representation for the electrochemical cell made using half cells (v) and (vi). e) Draw the diagram for the cell represented in (d) above. (3 marks) f) A current of 1.8 A was passed through molten aluminium oxide for 3 hrs. Calculate i) the number of faradays used.(f=96500c) ii) the moles of aluminium deposited iii) the mass of aluminium deposited ( Al = 27)

11 11 6. a)the set up below was used to obtain dry nitrogen gas from air. Study it and answer the questions that follow. Magnesium ribbon Combustion tube Nitrogen gas Water in Heat Syringe Water Solution Q Conc. Sulphuric acid (i) Name the method used above. (ii) Identify solution Q. (iii) State the observation made in the combustion tube. (iv) What is the function of concentrated sulphuric acid in the set up above. (v) Name one impurity in the nitrogen gas collected by this method.

12 12 b) The set up below was used to prepare Nitric (v) acid in the laboratory using concentrated sulphuric acid on potassium nitrate crystals. Study it and answer the questions that follow. Cold water Conc. H2SO4 KNO3 Nitric acid Heat (i) Explain why sodium nitrate is not appropriate option in place of potassium nitrate. (ii) A reddish brown gas was observed in the retort. Explain. (2 mark) (iii) Copper reacts with the nitric acid formed but does not react with hydrochloric acid. Explain. (2 mark) c) 60 50% Nitric (v) acid is produced from the absorption chamber in the industrial manufacture of the nitric acid. Describe how the percentage of the acid can be increased.