0620-CHEMISTRY - CAMBRIDGE - IGCSE MODULE

2. What is an oxide?
• An oxide is a compound of oxygen and
another element.
• There are four types of oxides:
- acidic oxides
- basic oxides
- amphoteric oxides
- neutral oxides

3. Acidic Oxides
• Non-metals may form acidic oxides.
• Most acidic oxides dissolve in water to
form an acid.
• One example is sulphur dioxide, which
dissolves readily in water to form sulphurous
acid.
• Acidic oxides are often gases at room
temperature.

4. Acidic oxide Formula Physical
state
Acid produced in
water
Name formula
Carbon dioxide CO2 Gas Carbonic
acid
H2CO3
Sulphur
trioxide
SO3 Gas Sulphuric
acid
H2SO4
Phosphorus(V)
oxide
P4O10 solid Phosphoric
acid
H3PO4
Example:
SO2(g) + H2O(l)  H2SO3(aq)
sulphur dioxide + water  sulphurous acid
Acidic Oxides

5. • Acidic oxides do not react with acids.
• However, they react with alkalis to form a salt
and water.
Example:
SO2(g) + 2NaOH(aq)  Na2SO3(aq) + H2O(l)
sulphur dioxide + sodium hydroxide
 sodium sulphite + water
Acidic Oxides

6. Oxides
Acidic
oxide
oxides
of non-
metals
SO2,
CO2
SO3
acids
e.g. SO2 + H2O H2SO3 (sulphurous acid)
CO2 + H2O H2CO3 (carbonic acid)
SO3 + H2O H2SO4 (sulphuric acid)
salt + water
CO2 + Ca(OH)2 CaCO3 + H2O
SO2 + Ca(OH)2 CaSO3 + H2O
SO3 + NaOH Na2SO4 + H2O
CO2 turned limewater
chalky due to the
formation of calcium
carbonate which is an
insoluble solid.

7. Basic Oxides
• The oxides of metals are basic oxides.
• Most basic oxides are insoluble in water.
• Basic oxides are often solids at room
temperature.
• A few oxides, such as sodium oxide and
potassium oxide, dissolve readily in water.
They are called alkalis.

8. Examples:
• When calcium oxide (quicklime) is added to
water, a vigorous reaction occurs.
• Calcium hydroxide (limewater) is formed,
which is sparingly soluble in water.
Basic Oxides

9. • Basic oxides react with acids to form a salt and
water.
Example:
CaO(s) + 2HNO3(aq)  Ca(NO3)2(aq) + H2O(l)
calcium oxide + nitric acid
 calcium nitrate + water
This is a neutralisation reaction.
Basic Oxides

10. Oxides
Basic
oxide
oxides of
metals
CaO
CuO
Na2O
salt + water
CaO + HNO3
MgO + H2SO4
alkalis
(only some
basic oxide
dissolves in
water)
Na2O + H2O 2NaOH
CuO + H2O no reaction
Ca(NO3)2 + H2O
MgSO4 + H2O
2

11. • Zinc oxide is an example of an amphoteric
oxide.
• Amphoteric oxides are metallic oxides that
react with both acids and bases to form salts
and water.
Amphoteric Oxides

12. Reaction 1: 2HCl(aq) + ZnO(s)  ZnCl2(aq) + H2O(l)
hydrochloric acid + zinc oxide  zinc chloride + water
In reaction (1), zinc oxide behaves as a basic oxide.
Reaction 2: 2NaOH(aq) + ZnO(s)  Na2ZnO2(aq) + H2O(l)
sodium hydroxide + zinc oxide  sodium zincate + water
In reaction (2), it behaves as an acidic oxide.
Amphoteric Oxides
In both reactions, a salt and water are formed.
Examine these reactions

13. Oxides
amphoteric
oxide
ZnO
Al2O3
PbO
salt + water
salt + water
ZnO + HCl
Al2O3 + HNO3
PbO + H2SO4
ZnCl2 + H2O
2
Al(NO3)3 + H2O
3
PbSO4 + H2O
Zinc oxide + sodium hydroxide
Aluminium oxide + sodium hydroxide
Lead (II) oxide + sodium hydroxide
Sodium aluminate + water
Sodium plumbate + water
sodium zincate + water

14. Neutral Oxides
• Some non-metals form oxides that show neither
basic nor acidic properties.
• These oxides are called neutral oxides and they are
insoluble in water.
• Examples: Water (H2O), Carbon monoxide (CO),
Nitric oxide (NO)

15. Oxides
Acidic
oxide
oxides
of non-
metals
SO2,
CO2
SO3
acids
salt + water
Basic
oxide
Oxides of
metal
alkalis
salt + water
CaO
CuO
Na2O
Amphoteric
oxide
ZnO
Al2O3
PbO
salt + water
salt + water
Neutral oxide
Oxides of
non-metals
Does not react with
acids or alkalies
CO
H2O
NO