(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).
(a) An electrochemical cell is a device that converts chemical energy into electrical energy (or electrical energy into chemical energy) by means of redox reactions.
(b) I. Electrolyte: molten aluminium oxide (alumina, Al2O3) dissolved in molten cryolite.
II. Ore: bauxite.
III. Electrodes: carbon (graphite).
(ii) Cryolite is added to lower the melting point of the alumina (saving energy) and to increase the electrical conductivity of the electrolyte.
(c)(i) Two gaseous fuels from coke: water gas (CO + H2) and producer gas (CO + N2).
(ii) The better fuel is water gas.
(iii) Water gas has a higher calorific (heat) value because both its components (CO and H2) are combustible, whereas producer gas is diluted with inert nitrogen.
(iv) Water gas: \(C + H_2O \rightarrow CO + H_2\); Producer gas: \(2C + O_2 \rightarrow 2CO\).
(d)(i) Observations: I. chlorine through aqueous sodium iodide: the solution turns brown as iodine is liberated. II. chlorine over heated iron: brown (reddish-brown) fumes form and a brown solid, iron(III) chloride, is deposited. III. silver trioxonitrate(V) added to aqueous sodium bromide: a pale-yellow (cream) precipitate of silver bromide forms.
(ii) Equations:
I. \(Cl_2 + 2NaI \rightarrow 2NaCl + I_2\)
II. \(2Fe + 3Cl_2 \rightarrow 2FeCl_3\)
III. \(AgNO_3 + NaBr \rightarrow AgBr + NaNO_3\)
(a) An electrochemical cell is a device that converts chemical energy into electrical energy (or electrical energy into chemical energy) by means of redox reactions.
(b) I. Electrolyte: molten aluminium oxide (alumina, Al2O3) dissolved in molten cryolite.
II. Ore: bauxite.
III. Electrodes: carbon (graphite).
(ii) Cryolite is added to lower the melting point of the alumina (saving energy) and to increase the electrical conductivity of the electrolyte.
(c)(i) Two gaseous fuels from coke: water gas (CO + H2) and producer gas (CO + N2).
(ii) The better fuel is water gas.
(iii) Water gas has a higher calorific (heat) value because both its components (CO and H2) are combustible, whereas producer gas is diluted with inert nitrogen.
(iv) Water gas: \(C + H_2O \rightarrow CO + H_2\); Producer gas: \(2C + O_2 \rightarrow 2CO\).
(d)(i) Observations: I. chlorine through aqueous sodium iodide: the solution turns brown as iodine is liberated. II. chlorine over heated iron: brown (reddish-brown) fumes form and a brown solid, iron(III) chloride, is deposited. III. silver trioxonitrate(V) added to aqueous sodium bromide: a pale-yellow (cream) precipitate of silver bromide forms.
(ii) Equations:
I. \(Cl_2 + 2NaI \rightarrow 2NaCl + I_2\)
II. \(2Fe + 3Cl_2 \rightarrow 2FeCl_3\)
III. \(AgNO_3 + NaBr \rightarrow AgBr + NaNO_3\)
