A-Level Chemistry AQA Notes
3.2.4 Properties of Period 3 elements and their oxides (A-Level)
Properties of Period 3 Elements
- 2Na (s) + 2H2O (l) → 2NaOH (aq) + H2 (g) (fast reaction)
- Mg (s) + 2H2O (l) → Mg(OH)2 (aq) + H2 (g) (slow reaction)
- All of the Period 3 elements can react with oxygen to form oxides to form Na2O, MgO, Al2O3, SiO2, P4O10, SO2 and SO3
- Sodium burns with a yellow flame, magnesium burns with a white flame, aluminium with a brilliant white flame and sulfur with a blue flame.
- Na2O (s) + H2O (l) → 2NaOH (aq) pH 12-14
- MgO (s) + H2O (l) → Mg(OH)2 (aq) pH 9-10
These species can react in this way because they are purely ionic, so hydration can occur
- Aluminium oxide and silicon dioxide are both insoluble and do not react with water due to the strong covalent bonds
- When the non-metal oxides react with water, acidic solutions are formed.
P4O10 (s) + 6H2O (l) → 4H3PO4 (aq)
SO2 (g) + H2O (l) → H2SO3 (aq)
SO3 (l) + H2O (l) → H2SO4 (aq)
SO2 (g) + H2O (l) → H2SO3 (aq)
SO3 (l) + H2O (l) → H2SO4 (aq)
- The basic oxides act as bases and neutralise acids:
Na2O (s) + 2HCl (aq) → 2NaCl (aq) + H2O (l)
MgO (s) + H2SO4 (aq) → MgSO4 (aq) + H2O (l)
MgO (s) + H2SO4 (aq) → MgSO4 (aq) + H2O (l)
- The acidic oxides act as acids and neutralise bases:
SiO2 (s) + 2NaOH (aq) → Na2SiO3 (aq) + H2O (l)
P4O10 (s) + 12NaOH (aq) → 4Na3PO4 (aq) + 6H2O (l)
SO2 (g) + 2NaOH (aq) → Na2SO3 (aq) + H2O (l)
SO3 (l) + 2NaOH (aq) → Na2SO4 (aq) + H2O (l)
P4O10 (s) + 12NaOH (aq) → 4Na3PO4 (aq) + 6H2O (l)
SO2 (g) + 2NaOH (aq) → Na2SO3 (aq) + H2O (l)
SO3 (l) + 2NaOH (aq) → Na2SO4 (aq) + H2O (l)
- Al2O3 is an amphoteric oxide and can act as either an acid or base. It neutralises both acids and bases:
Al2O3 (s) + 3H2SO4 (aq) → Al2(SO4)3 (aq) + 3H2O (l)
Al2O3 (s) + 2NaOH (aq) + 3H2O (l) → 2NaAl(OH)4 (aq)
Al2O3 (s) + 2NaOH (aq) + 3H2O (l) → 2NaAl(OH)4 (aq)