GIRLS JUNIOR LYCEUM L-IMRIEĦEL HALF YEARLY EXAMINATIONS 2016/2017

Transcription

1 1 GIRLS JUNIOR LYCEUM L-IMRIEĦEL HALF YEARLY EXAMINATIONS 2016/2017 FORM: 4 CHEMISTRY Time: 1hr30min Name: Class: One mole of electrons carries a charge of 96500C or 1 Faraday 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 2 Section A Answer ALL questions in this section. (Total 60%) 1. State the colour of: (i) copper metal (ii) solid iodine (iii) Cu 2+ ions in aqueous solution (iv) the Bunsen flame when a crystal of lithium chloride is tested (v) zinc ions in aqueous solution (5 marks) 2. The following equation represents the reaction between 26,5g of sodium carbonate and dilute hydrochloric acid. Na2CO3(s) + 2HCl(aq) 2NaCl(aq) + H2O(l) + CO2(g) (a) How many moles are there in 26.5g sodium carbonate? (2) (b) How many moles of hydrochloric acid are needed to react with 26.5g of sodium carbonate? (1) (c) Calculate the greatest mass of sodium chloride which could be formed by the reaction of 26.5g of sodium carbonate. (3) (d) Calculate the volume of carbon dioxide liberated at s.t.p. by the reaction of 26.5g of sodium carbonate. (2)

3 3 3. Write balanced ionic equations, showing state symbols, for the following: (a) magnesium + lead(ii) nitrate solution (b) zinc + dilute nitric acid (c) silver nitrate + sodium chloride (d) Fluorine and potassium chloride solution (8) 4. This question concerns the elements of group 1, that is, alkali metals. (a) Why are group 1 metals stored under oil? (1) (b) Write an equation for the reaction of sodium metal with oxygen and state the colour of the flame. Colour: (1) Equation: (1) (c) Explain how the third member of this group reacts with water. Your answer should include what you would do, observations and an equation for the reaction taking place. Method: (2) Observations: (3) Equation: (2) (d) Write an equation for the thermal decomposition of sodium nitrate: (2)

4 4 5. For each of the following equations: (i) work out the oxidation numbers of the underlined element/ion, (ii) write a half equation to show how it changed from the left hand side to the right hand side of the equation (iii) state whether the element/ion has been oxidised, reduced or has undergone no change. a. 2NaCl(aq) + F2(g) 2KF(aq) + Cl2(s) Oxidation numbers: Half-equation: The element has been oxidised, reduced, no change b. 2Na(s) + Cl2(g) 2NaCl(s) Oxidation numbers: Half-equation: The element has been oxidised, reduced, no change c. 3Cu(s) + 8HNO3(aq) 3Cu(NO3)2(aq) + 4NO2(g) + 4H2O(l) Oxidation numbers: Half-equation: The element has been oxidised, reduced, no change d. Cu(s) + 2AgNO3(aq) Cu(NO3)2 + 2Ag(s) Oxidation numbers: Half-equation: The element has been oxidised, reduced, no change (12) 6. Complete the following table by giving the product at the positive electrode and the half-equation at the negative electrode when the following are electrolyzed using inert electrodes. (6) Copper(II) nitrate solution Concentrated sodium chloride solution Dilute sulphuric acid Positive electrode Half equation at the negative electrode

5 5 7. The following apparatus may be used for the electrolysis of molten lead(ii) bromide. carbon anode carbon cathode molten lead(ii) bromide HEAT a. Give ONE observation at the CATHODE and ONE at the ANODE. (i) (ii) (2) b. Find the quantity of electricity passed if a current of 5A is passed for an hour through the electrolyte. (1) c. Find the mass of products deposited at the cathode and anode by the passage of 5A for 1hour through the electrolyte. Anode Cathode (3) (3)

6 6 Section B Answer TWO questions from this section. Where appropriate, equations and diagrams should be given to clarify your answer. (Total 40%) 8. (a)draw a fully labeled diagram to show how the electrolysis of dilute sulphuric acid could be carried out and the gaseous products collected, measured and tested. Indicate clearly: (i) (ii) (iii) (iv) (v) the material from which the electrodes are made, the polarity of the electrodes, the gas collected at each electrode and the relative volume of each. Give also balanced ionic equations for the reactions taking place at each electrode. (14) (b) Describe simple tests (one for each gas) to identify the gases produced during the above process. (3) (c) The metal sodium can be produced industrially by the electrolysis of molten sodium chloride. What is the number of moles of electrons required to produce 46g of sodium in this process? (3) TOTAL = 20 marks 8. (a) Draw a labelled diagram of the apparatus you would use to compare the electrical conductivity of different solids and liquids. This may be in the form of circuit diagrams. (4) (b) Each of the substances below is tested using one of the circuits drawn in (a): deionized water, copper and molten lead(ii) bromide In each case, state what happens and briefly explain the results in terms of their chemical structure. (9) (c) Using the substances listed in (b) above, explain and distinguish between the terms electrolyte, non-electrolyte and conductor. (3) (d) Hydrochloric acid is described as a strong electrolyte whereas ethanoic acid as a weak electrolyte. Explain why this is so. (4) TOTAL = 20 marks

7 7 9. Give an explanation of the statements below: (a) Solid sodium chloride and distilled water do not conduct electricity, but an aqueous solution of sodium chloride is a good electrolyte. (5) (b) When zinc metal is added to an aqueous solution of copper (II) sulphate, a reddish brown precipitate is deposited. But no reaction occurs when copper metal is added to a solution of zinc sulphate. (5) (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. (5) (d) Hydrogen is used to prepare hydrogen chloride by direct reaction with chlorine according to the following equation: H2(g) + Cl2(g) 2HCl(g) (i) A volume of 60dm 3 of chlorine are mixed with 80dm 3 of hydrogen and the reaction started. Assuming that the reaction goes to completion, calculate the volume of hydrogen chloride produced. All volumes are measured at the same temperature and pressure. (ii) Now, calculate the total volume of gas at the end of the reaction. (5) TOTAL = 20 marks