Describe application of electrolysis
Application of electrolysis
- Industrial preparation of gases; Cl2, H2 and O2.
- Extraction of metal: metals above carbon in the reactivity series are almost all extracted by electrolysis.
Example Extraction of sodium.
Ore: molten NaCl
Anode: iron cylinder is cheap and has a melting point above the melting point of NaCl.
Cathode: carbon because it does not react with chloride.
Calcium chloride added to the mixture to
- lower the melting point of sodium chloride from 8000Cto 6000C,
- reduce solubility of sodium in molten sodium chloride,
- Lower the corrosive vapor of sodium chloride.
Sodium is collected in dry nitrogen to protecting it from reacting with air.
At the cathode At the anode
Na+ + e → Na 2Cl–– 2e → Cl2(g)
Setup
The setup is such chlorine produced does not react with sodium
- Preparation of sodium hydroxide
By electrolysis of concentrated solution of sodium chloride using carbon anode and mercury cathode. At the anode chlorine is liberated and at mercury cathode Na+ instead of H+ is discharged and dissolved in mercury to form mercury amalgam.
At the cathode At the anode
Na+ + e → Na 2Cl–– 2e → Cl2(g)
When sodium amalgam is dropped in water, sodium reacts to form sodium hydroxide and hydrogen gas.
2Na + 2H2O (l) →2NaOH (aq) + H2(g)
Sodium hydroxide is concentrated to form pellets.
This process is disadvantageous because it releases poisonous mercury into the environment
Setup
- Purification of copper
Anode: impure copper (dissolves)
Cu (s) – 2e → Cu2+ (aq)
Cathode (copper is deposited)
Cu2+ (aq) + 2e → Cu (s)
Electrolyte: copper sulphate solution
Copper migrated from the anode to the cathode.
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