1 One mole of electrons carries a charge of 96500C or 1 Faraday Q=It One mole of any gas occupies 22.4dm 3 at standard temperature and pressure (s.t.p.) Standard temperature is 0 0 C or 273K and standard pressure is 760mmHg.
2 SECTION A Answer ALL questions in this section which carries 60 marks. 1. Complete the sentences below, using words from the following list. Each word may be used once or not at all. lose, gain, ions, atoms, molten, anions, aqueous, cations, electrons, solid. Ionic compounds do not conduct electricity in the state because the are fixed in position. But such compounds do conduct electricity in the or state. move to the negative electrode where they electrons. Metal conduct electricity due to the movement of. 2. a. Define reduction in terms of the loss or gain of hydrogen. Reduction is b. Define oxidation in terms of the loss or gain of electrons. Oxidation is c. For each of the following equations, state with a reason which substance has been oxidised. (i) Fe2O3 + 3CO 2Fe + 3CO2 (ii) Mg + 2AgNO3 Mg(NO3)2 + 2Ag (iii) SO2 + 2H2S 3S + 2H2O (6 marks)
3 3. 7.5g of zinc were added to excess sulfuric acid. a. Write two observations for this reaction. b. Write a balanced chemical equation to represent this reaction. c. Write a balanced ionic equation for this reaction. d. Calculate the number of moles of zinc that reacted with the acid. e. Calculate the volume of hydrogen produced from this reaction at standard temperature and pressure.
4 4. A piece of zinc foil was dipped into a beaker containing copper(ii) sulphate solution as shown in the diagram below. The reactants were left for a whole day to allow them enough time to react. a. Write a balanced equation to represent this reaction, include state symbols. b. Describe TWO observations that would be noted a day following the start of this reaction. c. State giving reason, which substance in this reaction is acting as an oxidizing agent and which substance is acting as a reducing agent. d. What would you observe if a piece of silver metal had been dipped into the copper(ii) sulfate solution instead of zinc? Give a reason for your answer.
5 5. Butane, C4H10, burns in oxygen according to the following equation: 2C4H10 + 13O2 8CO2 + 10H2O A mixture contains 20 cm 3 of butane and 150cm 3 of oxygen at room temperature and pressure. The mixture is ignited and after the reaction takes place, the products are cooled back to room temperature. All gaseous volumes, before and after reaction, are measured at the same temperature and pressure. One of the reactants is not reacting completely. a. Use the equation given to work out which of the reactants remain in excess. (Hint: Use Guy Lussac s Law). b. Hence find the volume of unreacted butane or oxygen gas. c. Calculate the volume of carbon dioxide formed. (2 mark) d. Calculate the mass of water formed. e. Calculate the volume of the final gaseous mixture at room temperature and pressure.
6 6a. Pure water contains some ions. (i) Write the formulae of the ions present from pure water. (ii) Explain why pure water is poor conductor of electricity. (iii) Explain why a strong electrolyte, such as, sulphuric acid has to be added to water to be electrolysed. b. Electrolysis of dilute sulphuric acid produces two gases. At the anode (+): 25cm 3 of oxygen At the cathode (-): xcm 3 of a gas Y (i) What is gas Y? (ii) What is the value of x? (iii) State a simple test you would use to show that the gas formed at the anode was oxygen. (iv) Write a half- equation for the reaction that occurs at the anode and state with a reason whether this represents oxidation or reduction. Half-equation: Oxidation/Reduction and reason
7 7a. Fill in the empty spaces in the table below: Compound electrolysed 1. Lead (II) bromide State of compound Nature of electrodes Molten electrolyte; Graphite electrodes Observation at cathode Observation at anode 2. Concentrated CuCl2 solution aqueous electrolyte; platinum electrodes 3. Dilute sodium aqueous electrolyte; chloride platinum electrodes solution (6 marks) b. Identify the substance formed or the gas evolved in part (a) at: (i) the cathode in electrolysis 1: (ii) the anode in electrolysis 1: (iii) the anode in electrolysis 2: (iv) the anode in electrolysis 3: Section B Answer TWO questions from this section. (Total 40%) 8a. Rubidium, symbol Rb, is an alkali metal, following lithium, sodium and potassium in Group 1 of the Periodic Table. Describe what you would expect to be the appearance of rubidium metal. How would you expect it to react with water? Your answer should include what you would do, any observations and an equation for the reaction. (6marks)
8 b. Astatine, symbol At, is a halogen, following fluorine, chlorine, bromine and iodine in Group 7 of the Periodic Table. Describe what you would expect to be the appearance of astatine. Since astatine is below chlorine in group 7 in the Periodic Table, chlorine displaces astatide ions from potassium astatide solution. Write an equation for this reaction, including state symbols. (c) Rubidium and astatine form a compound called rubidium astatide. (i) What is the type of bonding in rubidium astatide. Draw a dot and cross diagram for this compound showing outer electrons only. Type of bonding: Dot and cross diagram: (ii) If molten rubidium astatide is electrolysed between inert electrodes, give the name of the products at each electrode and write equations for the reactions taking place. Name of products: Half-equation at anode: Half equation at cathode: Total 20 marks
9 9. Give an explanation for the statements below. Diagrams and equations may be used to illustrate your answer. (Use the foolscap provided to answer this question) (a) Solid sodium chloride and distilled water do not conduct electricity, but an aqueous solution of sodium chloride is a good electrolyte. (b) When magnesium metal is added to an aqueous solution of copper (II) sulfate, a reddish brown precipitate is deposited. But no reaction occurs when copper metal is added to a solution of magnesium sulfate. (c) When a strip of magnesium and another of copper are placed in dilute acid and connected together by means of a wire to a small electric bulb, the bulb lights up. (d) A solution of hydrogen chloride in toluene (methylbenzene) does not conduct electrolysis whereas hydrogen chloride dissolved in water is a strong electrolyte. Total 20 marks 10. During an experiment, it was intended to cover an iron spoon with silver. (Use the foolscap provided to answer this question) a. What is this process called? b. Draw a diagram to show how the apparatus has to be set up for this job to be carried out. c. Which ions are present in the silver nitrate solution? d. Write half-equations for reactions taking place at the cathode and the anode. e. Give the names of the products liberated and their ratio. f. What can be observed at: (i) the anode? (ii) the cathode? (iii) the solution g. The experiment is run for 30 minutes with a current of 50 Amps flowing through it. What mass of silver would have been deposited on the iron spoon after this time? h. Give one other industrial use of this electrolysis. Total 20 marks