(a) Define electrochemical cell.
(b) Aluminium can be prepared commercially by the application of electrolysis. Name the: I. electrolyte used in the process; II. ore from which the electrolyte is obtained; III. electrodes used in the electrolysis.
(ii) Give two reasons why cryolite, NaAl F(_6) is added to the electrolyte?
(c)(i) List the two gaseous fuels produced from coke.
(ii) Which of the two gases listed in (c)(i) is a better fuel?
(iii) Give a reason for your answer in (c)(i)
(iv) Write a balanced equation for the production of each gaseous fuel.
(d)(i) For each of the following reactions, state what would be observed when: I. chlorine gas is bubbled through aqueous sodium iodide; II. chlorine gas is passed over heated iron in a hard glass tube; III. aqueous silver trioxonitrate (V) is added to aqueous sodium bromide.
(ii) Write a balanced chemical equation for each of the reactions in (d)(i).
Explanation
(a) Definition of Electrochemical Cell: Electrochemical cell is defined as a device/cell which converts chemical energy to electrical energy/or electricity is generated by a chemical change.
(b) Aluminium can be prepared commercially by the application of electrolysis:
(i) Name the: I. Electrolyte used in the process: (i) Aluminium oxide/(Molten) alumina. II. Bauxite. III. Carbon electrodes/graphite electrodes.
(ii) Reasons why cryolite, NaAl F(_6) is added to the electrolyte: –As a solvent. –Helps reduce the melting point of alumina (Al(_2)O(_3)). –To increase the conductivity of electrolyte.
(c)(i) Gaseous fuels produced from coke: –Producer gas. –Water gas.
(c)(ii) Water gas.
(iii) Reason for your answer in(c)(ii): The producer gas contains about 67%/More non-combustible nitrogen and 33% less combustible carbon (II) oxide while water gas contains equal amount of combustible carbon (II) oxide and hydrogen.
(iv) Balance equation for each production of gaseous fuel: Producer gas. 2C(_{(s)}) + O2(_{2(g)}) + 4N(_{2(g)}) -> 2CO(_{(g)}) +4N(_{2(g)}). Water gas: C(_{(s)}) + H(_{2})O —> CO(_{(g)}) + H(_{2(g)})
(d)(i) What would be observed when:
I. Chlorine gas is bubbled through aqueous sodium iodide. –Colourless solution turn reddish brown.
II. Chlorine gas is passed over heated iron in a hard glass tube. –Grey silvery solid turns brown.
III. Aqueous silver trioxonitrate (V) is added to aqueous sodium bromide. –Cream/(pale) yellow precipitate.
(ii) Chemical equation for reactions in (d)(i):
(i) Cl(_2) +2Nal –> 2NaCl + l(_2)
(ii) 2Fe +3Cl(_{2}) —> 2FeCl(_{2})
(iii) AgNO(_{3}) +NaBr —> NaNO(_3) + AgBr.