(a) (i) Explain why the reaction of iron metal with dilute, aqueous hydrochloric acid gives iron (II) chloride and not iron (III) chloride.

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1 Summer 000 CH3 1. Use the following redox potential data to answer the questions that follow Electrode reaction E /V Fe(OH) 3 +e Fe(OH) + OH 0.56 Fe + +e Fe 0.44 Fe 3+ +3e Fe 0.04 H + +e 1/H /O +H O +e OH Fe 3+ +e Fe /Cl +e Cl Co 3+ +e Co (a) Explain why the reaction of iron mal with dilute, aqueous hydrochloric acid gives iron (II) chloride and not iron (III) chloride Suggest how an aqueous solution of iron (III) chloride could be made from iron mal. Justify your answer (b) Suggest, in outline, the stages in the rusting of iron, using the data above (Total 8 marks) 1

2 Summer 000 CH3. In the production of sodium hydroxide, brine is the raw material used. It is electrolysed in a diaphragm cell using a titanium anode and a steel cathode, separated by a porous asbestos diaphragm. (a) Outline the reasons for the used of the following in the production of sodium hydroxide by this mhod: brine, rather than sea water; an electrolytic process, rather than one where the mal is first produced and then reacted with water;.... a titanium anode, rather than a steel one; (Total 4 marks) 3. (a) When solid calcium nitrate is heated, brown fumes of nitrogen dioxide, NO, are seen and the solid remaining after decomposition is calcium oxide. Write a balanced equation for the thermal decomposition of calcium nitrate. Describe the changes you would see when cold water is added drop by drop to cold calcium oxide and give the chemical equation for the reaction.

3 Summer 000 CH3 State whher barium nitrate will decompose more easily or less easily than calcium nitrate on heating with a Bunsen burner. (iv) Account for the trend in the thermal stability of the nitrates of the elements in group. (b) The brown fumes in part (a) are not pure NO but a mixture of N O 4 and NO. N O 4 (g) Pale yellow NO (g) dark brown A transparent glass syringe was filled with the gaseous mixture of N O 4 and NO and its tip sealed. When the piston of the syringe was rapidly pushed well into the body of the syringe, thereby compressing the gas mixture considerably, the colour of the gas became momentarily darker but them became lighter again. Suggest why compressing the gases causes the mixture to darken. Explain why the mixture turns lighter on standing. Write an expression for the equilibrium constant, K p, for this equilibrium. 3

4 Summer 000 CH3 (iv) 1.0 mole of N O 4 was allowed to reach equilibrium at 400K. At equilibrium the partial pressure of N O 4 was found to be 0.15 atm. Given that the equilibrium constant K p for this reaction is 48 atm, calculate the partial pressure of NO in the equilibrium mixture. (Total 16 marks) 4. (a) A series of experiments was carried out on A, a compound of potassium, to dermine its identity. Some solid A was dissolved in distilled water. Aqueous silver nitrate acidified with dilute nitric acid was added and a cream precipitate was formed, which only slightly dissolved in dilute aqueous ammonia but was soluble in concentrated aqueous ammonia. Another sample of solid A was heated with concentrated sulphuric acid. The mixture of fumes produced was passed into water and the solution labelled B. The solution B was strongly acidic and coloured pale brown. A sample of solution B was mixed with an excess of an aqueous solution of potassium iodide when the colour turned to a very dark brown. The solution turned blue on adding one drop of starch solution but adding an excess of sodium thiosulphate solution removed the colour complely. Passing chlorine into an aqueous solution of A gave a dark brown liquid. Identify A Identify the component of the fumes which was responsible for the solution B being strongly acidic. Account for the production of the pale brown colour in solution B (iv) What was indicated by the starch solution turning blue? 4

5 Summer 000 CH3 (v) Write an ionic equation for the reaction which led to the disappearance of the blue colour on adding sodium thiosulphate. (vi) On the basis of these results it is possible to place three elements in order of their ability to act as oxidising agents. Give the names of these elements in order, with the most powerful oxidising agent first and the least powerful last. (b) Give the formula of a compound containing chlorine in the oxidation state +5 Write an ionic equation for the disproportionation of the chlorate(i) ion. (c) Give one large scale use of chlorine.... (Total 13 marks) 5. The Born-Haber cycle for the formation of sodium chloride from sodium and chlorine may be represented by a series of stages labelled A to F as shown. + 1 Na (g) + Cl (g) + e 1 Na(g) + Cl (g) 1 Na(s) + Cl (g) + Na (g) + Cl(g) + e A F B C E D Na (g) + Cl (g) + NaCl(s) 5

6 Summer 000 CH3 (a) Write the lters A to F next to the corresponding definition in the table below definition lter H/kJ mol 1 1 st ionisation energy of sodium 1 st electron affinity of chlorine the enthalpy of atomisation of sodium the enthalpy of atomisation of chlorine the lattice enthalpy of sodium chloride the enthalpy of formation of sodium chloride Calculate the enthalpy of formation of sodium chloride from the data given. (b) The lattice enthalpies can be calculated from theory as well as dermined experimentally. Experimental H/kJ mol 1 Theorical H/kJ mol 1 Sodium chloride Silver iodide Why is the experimental value of the lattice enthalpy of silver iodide ( 889kJmol 1 ) so different from the value calculated theorically?

7 Summer 000 CH3 (c) Explain the trend in first ionisation energies of the elements of Group 1 in the Periodic Table (Total 10 marks) 7