Electrolysis Of Molten Compounds

Electrolysis Of Molten Compounds

Process of breaking down compounds in molten or aqueous state into their constituent elements by passing electricity through them.

v  Anode (Positive electrode)

─       Negative ions or anions are attracted to anode.

─       Anion undergo discharge by releasing electrons to form neutral atoms.

v  Cathode (Negative electrode)

─       Positive ions or cations are attracted to cathode.

─       Cation  undergo discharge to form atoms.

Electrolysis Of Molten Lead (II) Bromide

v  Anode (Positive electrode)

─       Anions, Br ^- are attracted to the anode.

─       Bromide ions, Br^- discharge by releasing electron to form bromine gas, Br₂

Half equation :

2Br^-(l)      →       Br₂(g) + 2e^-

v  Cathode (negative electrodes)

─       Lead(II) ions, Pb²⁺ are attracted to the cathode.

─       Lead (II) ions, Pb²⁺ undergo discharge by accepting two electrons to form a lead atom/lead metal.

Half equation :

Pb²⁺ (I) + 2e^-       →         Pb (s)

Overall equation:

Pb²⁺ (I) + 2Br ^-  → Pb(s) + Br₂(g)

Electrolytes & Non-Electrolytes

Electrolytes

v  Substance that can conduct electricity in molten state or aqueous solution.

v  Contains free moving ion that carry electrical charges.

v  Ionic compounds such as molten lead (II) chloride, PbCI₂.

v  Acid solutions such as nitric acid, HNO₃.

Non-Electrolytes

v  Substance which cannot conduct electricity in all states.

v  Made from molecules only-no ions that can carry electrical charges and conduct electricity.

v  Covalent compounds such as alcohol, sugar and naphthalene.

Electrolysis of aqueous solution

Electrolysis of aqueous solution

1.     Electrolysis of potassium nitrate solution, KNO₃ using carbon electrodes.

	Anode (+)	Cathode (-)
Ion presents	NO-3, OH-	K+, H+
Half equation	4OH- → 2H2O + O2 +4e	2H+ + 2e → H2
Observation	Colourless gas bubbles are released	Colourless gas bubbles are released
Product	Oxygen gas	Hydrogen gas

2.     Electrolysis of silver nitrate solution, AgNO₃ using carbon electrodes.

	Anode (+)	Cathode (-)
Ion presents	NO-3, OH-	Ag+, H+
Half equation	4OH- → 2H2O + O2 +4e	Ag+ + e → Ag
Observation	Colourless gas bubbles are released	A grey solid is formed
Product	Oxygen gas	Silver metal

3.     Electrolysis of copper(II) sulphate solution, CuSO₄ using carbon electrodes.

	Anode (+)	Cathode (-)
Ion presents	SO2-4, OH-	Cu2+, H+
Half equation	4OH- → 2H2O + O2 +4e	Cu2+ + 2e → Cu
Observation	Colourless gas bubbles are released	Brown solid is formed
Product	Oxygen gas	Copper metal

4.     Electrolysis of concentrated potassium chloride solution, KCl using carbon electrodes.

	Anode (+)	Cathode (-)
Ion presents	Cl- , OH-	K+, H+
Half equation	Cl- → Cl2 + 2e	2H+ + 2e → H2
Observation	Greenish-yellow gas bubbles are released	Colourless gas bubbles are released
Product	Chlorine gas	Hydrogen gas

5.     Electrolysis of silver sulphate solution, Ag₂SO₄ using silver electrode as anode and carbon electrode as cathode.

	Anode (+)	Cathode (-)
Ion presents	-
Half equation	Ag→ Ag+ +e	Ag+ + e → Ag
Observation	Silver electrode corrodes and become thinner	A grey solid is deposited and electrode becomes thicker.
Product	Silver ion	Silver metal

6.     Electrolysis of copper(II) nitrate solution, Cu(NO₃)₂ using copper electrode as anode and carbon electrode as cathode.

	Anode (+)	Cathode (-)
Ion presents	-	-
Half equation	Cu → Cu2+ +2e	Cu2+ + 2e → Cu
Observation	Copper electrode corrodes and become thinner	Brown solid is deposited and electrode becomes thicker.
Product	Copper(II) ion	Copper metal