Half and Ionic Equations (GCSE)

CW 09/03/2024
Learning Objective:
write half equations
construct balanced ionic equations.
Keywords: Electrons, charges, balance.
Starter Task:
1. How many electrons does magnesium lose when it becomes an io
2. How many electrons does oxygen gain when it becomes an ion?
3. How many electrons does sodium lose when it becomes an ion?
4. How many electrons does chlorine gain when It becomes an ion?
5. How many electrons does barium lose when it becomes an ion?
OILRIG An easy way to remember what happens to the electrons
during oxidation and reduction is to think OILRIG:
Equations written to show what happens to electrons during

oxidation and reduction are called half-equations.
The half equations for the

reaction of copper sulfate
and zinc are:
reduction:
Cu2+(aq) + 2e- Cu (s)
Ions you should know
• Cations (positive – metals) Anions (negative – non
metals)
• Na+ sodium Cl- chloride
• K+ potassium F- fluoride
• Mg2+ magnesium Br- bromide
• Ca2+ calcium O2- oxide
• Fe2+ iron (II) OH- hydroxide
• Cu2+ copper (II) NO3- nitrate
• Li+ lithium SO42- sulfate
• Ag+ silver HCO3- hydrogen carbonate
• NH4+ ammonium CO32- carbonate
Types of Equations
Word Equations: Describe the reaction and name the substances
Copper sulphate + magnesium à magnesium sulphate + copper
Chemical Equations: Show the whole reaction

CuSO4 (aq) + Mg(s) à MgSO4 (aq) + Cu(s)
Ionic Equations: Only shows how oppositely charged ions form ionic
compounds.
Cu2+ (aq) + Mg(s) à Mg2+(aq) + Cu(s)
Half Equations Only shows ions and the movement of electrons.

Cu2+ (aq) + 2e- à Cu(s) and Mg(s) à Mg2+(aq) + 2e-
1) What is the definition of oxidation and reduction?
2) Complete these half equations:

a) …Cl- à Cl2 +… e-
b) …O2- à O2 +… e-
c) Ca2+ +… e- à Ca
d) Al3+ +… e- à Al
e) …N3- à N2 + …e-
f) …H+ + …e- à H2
Writing ionic equations
The reaction of solid sodium (Na) and hydrochloric acid (HCl)
can be written to show the ionic components of the reaction.
What is the balanced ionic equation for this reaction?
1. First split the aqueous ionic compounds into their

separated (dissociated) ions:
Writing ionic equations
remember your
state symbols!
Na+ (aq) + OH- (aq) + H+ (aq) + Cl- (aq) Na+ (aq) + Cl- (aq) + H2O(l)
These are called spectator ions

Na+ (aq) + OH- (aq) + H+ (aq) + Cl- (aq) Na+ (aq) + Cl- (aq) + H2O(g)
Ionic equations and redox reactions
A redox reaction is a reaction in which both oxidation and reduction are
occurring.
For example, the reaction of solid zinc and aqueous copper(II) sulfate solution.
What is the net ionic equation for this reaction?

Ionic equations and redox reactions
A redox reaction is a reaction in which both oxidation and reduction are
occurring.
For example, the reaction of solid zinc and aqueous copper(II) sulfate solution.
What is the net ionic equation for this reaction?
Which species are oxidised and which are reduced?

Producing Ionic Equations for Redox Reactions
• Redox reactions involve REDUCTION and OXIDATION
REDUCTION = gain of electrons OXIDATION = loss of electrons
Displacement reactions involve redox. One metal gains electrons, while the
other loses them. There are also SPECTATOR ions that we need to identify
and ignore!
Magnesium(s) + copper(II) sulphate(aq) à magnesium sulphate(aq) +
copper(s)
Cu2+(aq) + SO42- (aq) + Mg(s) à Mg2+(aq) + SO42- (aq) + Cu(s)
SPECTATOR ions
• Redox reactions involve REDUCTION and OXIDATION
REDUCTION = gain of electrons OXIDATION = loss of electrons
Displacement reactions involve redox. One metal gains electrons, while the
other loses them. There are also SPECTATOR ions that we need to identify
and ignore!
copper(s)
SPECTATOR ions
copper(s)
SPECTATOR ions
These are the same on both sides and should be cancelled out
Cu2+(aq) + Mg(s) à Mg2+(aq) + Cu(s)

Magnesium(s) + sulphuric acid(aq) à magnesium sulphate(aq) +
hydrogen(g)
H2SO4 (aq) + Mg(s) à MgSO4 (aq) + H2(g)
2H+(aq) + SO42- (aq) + Mg(s) à Mg2+(aq) + SO42- (aq) + H2 (g)
SPECTATOR ions Hydrogen

has
changed
2H (aq) + SO4 (aq) + Mg(s) à Mg (aq) + SO4 (aq) + H2 (g)
+ 2- 2+ 2-
state so it
must be left
2H+(aq) + Mg(s) à Mg2+(aq) + H2 (g) in the ionic
equations
Magnesium(s) + sulphuric acid(aq) à magnesium sulphate(aq) +
hydrogen(g)
H2SO4 (aq) + Mg(s) à MgSO4 (aq) + H2(g)
2H+(aq) + SO42- (aq) + Mg(s) à Mg2+(aq) + SO42- (aq) + H2 (g)
SPECTATOR ions Hydrogen

has
changed
2H (aq) + SO4 (aq) + Mg(s) à Mg (aq) + SO4 (aq) + H2 (g)
+ 2- 2+ 2-
state so it
must be left
2H+(aq) + Mg(s) à Mg2+(aq) + H2 (g) in the ionic
equations
Practice
Write ionic equations for the following chemical equations
1. Ca(NO3)2(aq) + 2Na(s) à 2NaNO3(aq) + Ca(s)
2. Na2CO3(aq) + 2K(s) + K2CO3(aq) + 2Na(s)
3. FeSO4(aq) + Zn(s) à ZnSO4(aq) + Fe(s)
4. Fe2(SO4)3 + 3Zn(s) à 3ZnSO4(aq) + 2Fe (s)
5. 2HCl(aq) + Fe(s) à FeCl2(aq) + H2(g)
6. 2HNO3(aq) + Mg(s) à Mg(NO3)2(aq) + H2(g)
Extension
• Zinc(s) + copper(II) sulphate(aq) à zinc sulphate(aq) + copper(s)
• Calcium nitrate(aq) + potassium(s) à potassium nitrate(aq) + calcium(s)
• lithium sulphate(aq) + sodium(s) à
Practice
1. Ca2+ (aq) + 2Na(s) à 2Na+ (aq) + Ca(s)
2. 2Na+ (aq) + 2K(s) à 2K+ (aq) + 2Na(s)
3. Fe2+ (aq) + Zn(s) à Zn2+ (aq) + Fe(s)
4. 2Fe2+(aq) + 3Zn(s) à 3Zn2+ (aq) + 2Fe (s)
5. 2H+ (aq) + Fe(s) à Fe2+ (aq) + H2(g)
6. 2H+ (aq) + Mg(s) à Mg2+ (aq) + H2(g)
Extension
• Zinc(s) + copper(II) sulphate(aq) à zinc sulphate(aq) + copper(s)
• Calcium nitrate(aq) + potassium(s) à potassium nitrate(aq) + calcium(s)
• lithium sulphate(aq) + sodium(s) à
Practice
1. Ca2+ (aq) + Na(s) à 2Na+ (aq) + Ca(s)
2. 2Na+ (aq) + 2K(s) à 2K+ (aq) + 2Na(s)
3. Fe2+ (aq) + Zn(s) à Zn2+ (aq) + Fe(s)
4. 2Fe2+(aq) + 3Zn(s) à 3Zn2+ (aq) + 2Fe (s)
5. 2H+ (aq) + Fe(s) à Fe2+ (aq) + H2(g)
6. 2H+ (aq) + Mg(s) à Mg2+ (aq) + H2(g)
Extension
• Zn(s) + CuSO4(aq) à Cu(s) + ZnSO4(aq) Zn(s) + Cu2+(aq) à Cu(s) + Zn2+(aq)
• Ca(NO3)2(aq) + 2K(s) à 2KNO3(aq) + Ca(s) Ca2+(aq) + 2K(s) à 2K+(aq) + Ca(s)
• Li2SO4(aq) + 2Na(s) à Na2SO4(aq) + 2Li(s) Li+(aq) + Na(s) à Na+(aq) + Li(s)
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CW 09/03/2024

Equations written to show what happens to electrons during

The half equations for the

Chemical Equations: Show the whole reaction

Half Equations Only shows ions and the movement of electrons.

2) Complete these half equations:

What is the balanced ionic equation for this reaction?

1. First split the aqueous ionic compounds into their

These are called spectator ions

What is the net ionic equation for this reaction?

What is the net ionic equation for this reaction?

Which species are oxidised and which are reduced?

Cu2+(aq) + Mg(s) à Mg2+(aq) + Cu(s)

SPECTATOR ions Hydrogen

SPECTATOR ions Hydrogen

TWEET ME Call my bluff!

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