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LAB EXERCISE 2 FOR CHEM 2032A
- Institution
- University Of The Witwatersrand (wits)
EXERCISE 2 FOR CHEMISTRY AND ALSO LAB 4 FOR CHEM2032A
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Lab Exercise 2Lumu – P 2432041
Question 1
1.1 Because the discharge potential of the Al3+ ion is higher than that of the H+ ion, if we
use an aqueous solution of aluminium salt, the hydronium ions are preferable
discharged at the cathode, resulting in H2 gas, while Al remains in the solution. As a
result, we are unable to obtain Aluminium metal through electrolysis. Because of the
high reactivity of aluminium metal, it is impossible to create elemental aluminium by
electrolysis of aqueous aluminium salts. The aluminium would react with the protons
in the water to form strong chemical bonds, resulting in hydrogen gas. As a result,
the expected result would not occur.
1.2 The Hall-Héroult procedures shared the same fundamentals and are still used in the
aluminium industry today. Direct current electrolysis is used to dissolve purified
alumina in molten cryolite. The oxygen in the alumina is deposited on the carbon
anode and released as carbon dioxide under the influence of the current, whereas
free molten aluminium—which is heavier than the electrolyte—is deposited on the
carbon lining at the bottom of the cell and released as carbon dioxide.
The overall reaction is:
2Al2O3 + 3C → 4Al + 3CO2
The electrolytic reactions are:
At the cathode: Al 3+ + 3e– → Al (l)
At the anode: C (s) + O2- → CO (g) + 2e–
C (s) + 2O2- → CO2 (g) + 4e–
Positively charged aluminium ions gain electrons from the cathode during the
electrolysis process. Oxide ions lose their anode electrons and produce oxygen
molecules. Solid carbon is converted to CO2 gas at the carbon anodes. CO2 is
emitted into the atmosphere. Aluminium ions are converted to elemental aluminium
at the carbon cathode, resulting in molten aluminium.
Carl Josef Bayer invented the Bayer process, which is the most used commercial
method for converting bauxite into alumina (aluminium oxide). Bauxite, the most
important aluminium resource, has only 30–60 percent aluminium oxide (Al2O3), with
the rest consisting of silica, different iron oxides, and titanium dioxide. A mildly
concentrated sodium hydroxide solution is used to treat crushed bauxite. The
concentration, temperature, and pressure employed are determined by the type of
aluminium oxide present in the bauxite and its source. Temperatures range from 140
to 240 degrees Celsius, with pressures reaching 35 atmospheres. Water in the
sodium hydroxide solution must be kept liquid at temperatures above 100°C, which
necessitates high pressures. The more pressure is required, the higher the
temperature. Aluminium oxide combines with sodium tetrahydroxoaluminate in a
heated concentrated sodium hydroxide solution.
Al2O3+2NaOH+3H2O⟶2NaAl(OH)4
The ore is first converted into pure aluminium oxide by the Bayer Process, and this is
then electrolyzed in solution in molten cryolite - another aluminium compound. The
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