55
Topic 5
Electricity & chemistry
Code Student Learning Objectives
Define electrolysis as the breakdown of an ionic compound, molten or in aqueous solution, by the
LO 5.1.1
passage of electricity
Describe the electrode products and the observations made during the electrolysis of:
–– molten lead(II) bromide
–– concentrated hydrochloric acid
LO 5.1.2
–– concentrated aqueous sodium chloride
–– dilute sulfuric acid
between inert electrodes (platinum or carbon)
State the general principle that metals or hydrogen are formed at the negative electrode (cathode),
LO 5.1.3
and that non-metals (other than hydrogen) are formed at the positive electrode (anode)
LO 5.1.4 Predict the products of the electrolysis of a specified binary compound in the molten state
LO 5.1.5 Describe the electroplating of metals
LO 5.1.6 Outline the uses of electroplating
Relate the products of electrolysis to the electrolyte and electrodes used, exemplified by the
LO 5.1.7 specific examples in the Core together with aqueous copper(II) sulfate using carbon electrodes
and using copper electrodes (as used in the refining of copper)
Describe electrolysis in terms of the ions present and reactions at the electrodes in the examples
LO 5.1.8
given
LO 5.1.9 Predict the products of electrolysis of a specified halide in dilute or concentrated aqueous solution
LO 5.1.10 Construct ionic half-equations for reactions at the cathode
IGCSE chemistry guide AOUDI . T.A. 2019
, 56
Electrolysis: the breakdown of an ionic compound(electrolyte), molten or in
aqueous solution, by the passage of electricity
Electrolysis requires energy therefore; it is an endothermic process.
2Al2O3 (liq) ⎯energy
⎯⎯→ 4Al (liq) + 3O2(g)
Electrolytes: are liquids that conduct electricity due to the presence of free ions.
e.g molten salts & aqueous solutions of acid, alkalis & salts.
In solid state, ions are tightly held by strong electrostatic forces(ionic bonds) in a
crystal lattice, so the ions are not free to move about i.e. can't flow.
Solid PbBr2 does NOT conduct electricity.
In the liquid (solutions) or molten state, the ions are free to move about & can
carry electric current (charge).
An aqueous solution of sugar contains no ions because sugar molecules do not
split into ions so it is a non-electrolyte.
IGCSE chemistry guide AOUDI . T.A. 2019
, 57
Electrolysis of molten ionic compounds
1. The electrolysis of molten PbBr2
PbBr2(liq) ⎯
⎯→ Pb(l) + Br2(g)
Lead(II) bromide ⎯
⎯→ lead + bromine
PbBr2(l)
Pb2+ to -ve Br¯ to + ve
Flow of
electrons
Brown fumes Graphite or Pt rod
of Br2(g) cathode
Molten lead bromide salt A Silvery grey of molten
PbBr2(s) is strongly heated in a metal
crucible. Heat
Anode reaction & Observation Cathode reaction & Observation
OIL RIG
Ions lose electrons [Oxidation] Ions gain electrons [Reduction]
2Br¯(liq) ⎯
⎯→ Br2(g) + 2e¯ Pb2+(liq) + 2e¯ ⎯
⎯→ Pb(l)
Red-brown fumes as Br2(g) bubbles A silvery grey layer (drips) of molten
off lead metal appears below the cathode
IGCSE chemistry guide AOUDI . T.A. 2019
Topic 5
Electricity & chemistry
Code Student Learning Objectives
Define electrolysis as the breakdown of an ionic compound, molten or in aqueous solution, by the
LO 5.1.1
passage of electricity
Describe the electrode products and the observations made during the electrolysis of:
–– molten lead(II) bromide
–– concentrated hydrochloric acid
LO 5.1.2
–– concentrated aqueous sodium chloride
–– dilute sulfuric acid
between inert electrodes (platinum or carbon)
State the general principle that metals or hydrogen are formed at the negative electrode (cathode),
LO 5.1.3
and that non-metals (other than hydrogen) are formed at the positive electrode (anode)
LO 5.1.4 Predict the products of the electrolysis of a specified binary compound in the molten state
LO 5.1.5 Describe the electroplating of metals
LO 5.1.6 Outline the uses of electroplating
Relate the products of electrolysis to the electrolyte and electrodes used, exemplified by the
LO 5.1.7 specific examples in the Core together with aqueous copper(II) sulfate using carbon electrodes
and using copper electrodes (as used in the refining of copper)
Describe electrolysis in terms of the ions present and reactions at the electrodes in the examples
LO 5.1.8
given
LO 5.1.9 Predict the products of electrolysis of a specified halide in dilute or concentrated aqueous solution
LO 5.1.10 Construct ionic half-equations for reactions at the cathode
IGCSE chemistry guide AOUDI . T.A. 2019
, 56
Electrolysis: the breakdown of an ionic compound(electrolyte), molten or in
aqueous solution, by the passage of electricity
Electrolysis requires energy therefore; it is an endothermic process.
2Al2O3 (liq) ⎯energy
⎯⎯→ 4Al (liq) + 3O2(g)
Electrolytes: are liquids that conduct electricity due to the presence of free ions.
e.g molten salts & aqueous solutions of acid, alkalis & salts.
In solid state, ions are tightly held by strong electrostatic forces(ionic bonds) in a
crystal lattice, so the ions are not free to move about i.e. can't flow.
Solid PbBr2 does NOT conduct electricity.
In the liquid (solutions) or molten state, the ions are free to move about & can
carry electric current (charge).
An aqueous solution of sugar contains no ions because sugar molecules do not
split into ions so it is a non-electrolyte.
IGCSE chemistry guide AOUDI . T.A. 2019
, 57
Electrolysis of molten ionic compounds
1. The electrolysis of molten PbBr2
PbBr2(liq) ⎯
⎯→ Pb(l) + Br2(g)
Lead(II) bromide ⎯
⎯→ lead + bromine
PbBr2(l)
Pb2+ to -ve Br¯ to + ve
Flow of
electrons
Brown fumes Graphite or Pt rod
of Br2(g) cathode
Molten lead bromide salt A Silvery grey of molten
PbBr2(s) is strongly heated in a metal
crucible. Heat
Anode reaction & Observation Cathode reaction & Observation
OIL RIG
Ions lose electrons [Oxidation] Ions gain electrons [Reduction]
2Br¯(liq) ⎯
⎯→ Br2(g) + 2e¯ Pb2+(liq) + 2e¯ ⎯
⎯→ Pb(l)
Red-brown fumes as Br2(g) bubbles A silvery grey layer (drips) of molten
off lead metal appears below the cathode
IGCSE chemistry guide AOUDI . T.A. 2019
