1 Our country, our future 525/2 S6 CHEMISTRY Exam 1 PAPER 2 DURATION: 2 HOUR 30 MINUTES For Marking guide contact and consultations: Dr. Bbosa Science 0776 802709. INSTRUCTIONS TO CANDIDATES Answer five questions, including three questions from section A and any two from section B Begin each question on a fresh page. Graph papers are provided. Non-programmable scientific calculators may be used
2 SECTION A (do any 3 numbers) 1. (a) State what meant by the term boiling point constant of a liquid. (2marks) (b) Describe an experiment that can be used to determine the relative molecular mass of a compound using the method of elevation of the boiling point of a liquid. Draw a labeled diagram of the apparatus used. (9marks) (c) Explain why the method you have described in (b) is not suitable for determination of the relative molecular mass of polymers in aqueous solution. (d) Calculate the freezing point of a solution containing 0.42g of ethane-1,2-diol (molecular mass =62) in 30g of water. (Kf of water =1.86 0 Cmol -1 kg -1 ) (e) When a compound Y, was steam distilled at standard pressure, the temperature of distillation was 96 0 C, the vapour pressure of water at this temperature was 730mmHG and the distillate contained 74% of water. Calculate the molar mass of Y. 2. (a) Write the formula and name of an ore of aluminium. (2marks) (b) Describe the process of extraction of pure aluminium metal from its ore (7marks) (c) Statethe conditions and write equations for the formation of aluminium chloride from the metal (3marka) (d) The relative molecular mass of aluminium chloride in a vapour phase is 267. (i) Write the molecular formula of aluminium chloride in a vapour phase. (ii) Write a structural formula to show the bonding in aluminium chloride vapour. (iii) Note the types of bonds involved in the structure you have drawn in (ii) above. (1marks) (e) With reference to aluminium oxide, explain the term amphoteric property. Write appropriate equations. (2marks) (f) Explain, giving the necessary equations, why, (i) solutions of simple Al 3+ salts are acidic. (ii) aluminium utensils should not be washed in strong alkaline solution (1mark) (1mark) 3. (a) What is molar conductivity? (1mark) (b) The molar conductivity of sodium hydroxide solutions of different concentration are shown in the table below
3 Concentration/moldm -3 0.01 0.04 0.09 0.14 0.25 0.36 Molar conductivity Λ/Ω -1 cm 2 mol -1 238 230 224 217 210 202 (i) Draw a graph of molar conductivity against the square root of concentration (ii) Explain the shape of the graph (04½ marks) (iii) Determine the value of molar conductivity at infinite dilution of sodium hydroxide and indicate its units. (c) Using the same conductivity cell, the resistance of 0.1M potassium chloride solution and 0.1M bromoethanoic acid solution were found to be 24.96 and 66.50 ohms respectively at 25 0 C. [The conductivity of potassium chloride at 25 o C is 0.01164Ω -1 cm -1 and molar conductivity of bromoethanoic acid at infinite dilution is 389Ω -1 cm 2 mol -1.] (i) Calculate the cell constant (ii) Calculate the molar conductivity of 0.1M bromoethanoic acid (iv) Determine the ph of 0.1M bromoethanoic acid (4 ½ marks) 4. Complete the following equations and in each case write the mechanism for the reaction. (a) CH 3 CH 2 CHO +H 2 NOH H + O (b) + CH 3 CCl AlCl 3 OH (c) Conc. H 3 PO 4 heat (3 marks) (d) (CH 3 ) 3 C CH 2 + Cl 2 H 2 O (e) CH 3 CHO + NaHSO 3 (3marks) CH 2 I (f) OH (2marks)
4 SECTION B (Any two numbers) 5. Write equations to show the following compounds can be synthesized. (a) CH 3 CH 2 CH 2 CO 2 H from propan-1-ol (b) CH 3 CH 2 CH 3 from 1-bromobutane (c) C CCH 3 from CH 2 CH 2 OH (6marks) H 3 C (d) H 3 C C N-NH NO 2 from propane 3.5marks) O2 N (e) CH 2 OH from benzene (2,5marks) 5. (a) (i) Explain why fluorine shows some differences in its properties from the rest of the group 7 elements (chlorine, bromine, and iodine) of the periodic table: (ii) State the different between the Chemistry of fluorine and the rest of the elements of group VII of PT. (b) Describe one general method for preparing the halogens (excluding fluorine) in the laboratory and write equations for the reactions. (3marks) (8marks) (4½ marks) (ii) (iii) How can you distinguish between sodium bromide and sodium iodide, given chlorine water and tetrachloromethane The acidity of halogens acids decrease in the order HI>HBr>HCl although their ionic characters increase in the reverse order. (3 marks) (2 ½ marks)
5 7. Carbon, silicon, tin and lead are elements in group IV of the periodic table. (a) State (i) the common oxidation state of group (IV) elements of the periodic table (01marks) (ii) how the stability of the oxidation states of group IV element vary down the group. (Illustrate your answer with the chloride of carbon and lead) (b) Give a reason for your answer in (a)(ii) (01marks) (c) Discuss the reaction of the chloride of each element with water (06marks) (d) Write equations for the reactions between (i) the oxide of each element and sodium hydroxide (06marks) (ii) lead (IV) oxide and concentrated hydrochloric acid (iv) Lead (IV) oxide and warm concentrated hydrochloric acid 8. Briefly explain each of the following observation: (a) Sodium chloride melts at 800 0 C whereas aluminium chloride sublimes at 180 0 C. (b) Graphite and copper are both conductors of electricity. (c) Iodine is much more soluble in potassium iodide than water. (d) A solution of sodium thiosulphate become cloudy with the formation of a yellow precipitate when left in air. (e) Phenylamine is a weaker base than ethylamine. (f) Phenol is a stronger acid than cyclohexanol. END