Candidates should be able to:
(a) (i) calculate oxidation numbers of elements in compounds and ions
(ii) describe and explain redox processes in terms of electron transfer and/or changes in oxidation number (oxidation state)
(iii) use changes in oxidation numbers to help balance chemical equations
(b) explain, including the electrode reactions, the industrial processes of:
(i) the electrolysis of brine, using a diaphragm cell
(ii) the extraction of aluminium from molten aluminium oxide/cryolite
(iii) the electrolytic purification of copper
(a) (i) calculate oxidation numbers of elements in compounds and ions
(ii) describe and explain redox processes in terms of electron transfer and/or changes in oxidation number (oxidation state)
(iii) use changes in oxidation numbers to help balance chemical equations
(b) explain, including the electrode reactions, the industrial processes of:
(i) the electrolysis of brine, using a diaphragm cell
(ii) the extraction of aluminium from molten aluminium oxide/cryolite
(iii) the electrolytic purification of copper
Chapter 7
Electrolysis – the decomposition of a compound into its elements by an electric current.
Electrolyte- the compound , either molten ionic compound or concentrated aqueous solution of ions, which is broken down.
Electrodes – rods made from carbon (graphite) or metal, which conduct electricity to and from the electrolyte.
Anode – positive , attracts anions which loses electrons making it an oxidation (electrons on right of equation)
Cathode - negative , attracts cations which gains electrons making it a reduction (electrons of the left of equation)
Extracting aluminum from bauxite ore (A soft, whitish to reddish-brown rock consisting mainly of hydrous aluminum oxides and aluminum hydroxides along with silica, silt, iron hydroxides, and clay minerals. Bauxite forms from the breakdown of clays and is a major source of aluminum.)
Aluminium is manufactured by the electrolysis of a molten mixture of aluminium oxide and cryolite.
· Aluminium forms at the negative electrode (cathode) and oxygen at the positive electrode (anode).
· The positive anode is made of carbon(graphite), which reacts with the oxygen to produce carbon dioxide.
Cryolite is used to dissolve the aluminum oxide so that the melting point of the electrolyte is lowered to about 970 degrees. It improves the electrical conductivity of the electrolyte.
Electrolysis of Brine
Electrolyte is sodium chloride(brine)
Anodes (+) are titanium, chloride and hydroxide move here (oxidized)
Cathodes (-) are steel, sodium and hydrogen move here (reduced)
Electrolysis – the decomposition of a compound into its elements by an electric current.
Electrolyte- the compound , either molten ionic compound or concentrated aqueous solution of ions, which is broken down.
Electrodes – rods made from carbon (graphite) or metal, which conduct electricity to and from the electrolyte.
Anode – positive , attracts anions which loses electrons making it an oxidation (electrons on right of equation)
Cathode - negative , attracts cations which gains electrons making it a reduction (electrons of the left of equation)
Extracting aluminum from bauxite ore (A soft, whitish to reddish-brown rock consisting mainly of hydrous aluminum oxides and aluminum hydroxides along with silica, silt, iron hydroxides, and clay minerals. Bauxite forms from the breakdown of clays and is a major source of aluminum.)
Aluminium is manufactured by the electrolysis of a molten mixture of aluminium oxide and cryolite.
· Aluminium forms at the negative electrode (cathode) and oxygen at the positive electrode (anode).
· The positive anode is made of carbon(graphite), which reacts with the oxygen to produce carbon dioxide.
Cryolite is used to dissolve the aluminum oxide so that the melting point of the electrolyte is lowered to about 970 degrees. It improves the electrical conductivity of the electrolyte.
Electrolysis of Brine
Electrolyte is sodium chloride(brine)
Anodes (+) are titanium, chloride and hydroxide move here (oxidized)
Cathodes (-) are steel, sodium and hydrogen move here (reduced)