Tuesday, 20 January 2015

6.2 Electrolysis of Molten Compounds

Electrolysis process
■ Electrolysis

A decomposition process of an electrolyte by an electric current into its components.
■ Electrolytic cell

A type of cell which uses electrical energy to produce chemical reaction.

The animation below shows the basic structure of an electrolytic cell
■ This video contains information about electrolysis of molten compounds.

Laboratory Activity 6.2.1: Electrolysis of molten compounds
Predicting products of electrolysis of molten compounds
■ Electrolysis of molten AxBy electrolyte

Metal compound is formed at the cathode.

Non-metal is formed at the anode.

In general, the electrolysis of molten electrolyte can be summarized as shown in the following table:
Salt in molten state At anode (+) At cathode (-)
Movements of ion to electrode Bx- Ay+
Half equation Bx- → B + xe- Ay++ ye- → A

Half-equation shows what happens at one of the electrodes during electrolysis.
Worked-example 6.2(a)
Predict the products of electrolysis of molten sodium chloride at anode and cathode.

Solution 
Salt in molten state At anode (+) At cathode (-)
Movements of ion to electrode Cl- Na+
Half equation 2Cl- → Cl2 + 2e- Na++ e- → Na
Observation Greenish-yellow gas Grey metal is formed
Product Chlorine gas Sodium metal

Worked-example 6.2(b)
Predict the products of electrolysis of molten magnesium oxide at anode and cathode.

Solution 
Salt in molten state At anode (+) At cathode (-)
Movements of ion to electrode O2- Mg2+
Half equation 2O2- → O2 + 4e- Mg2++ 2e- → Mg
Observation Colourless gas are released Grey metal is formed
Product Oxygen gas Magnesium metal


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