Oxides of period 3

The oxides of Period 3, Na - Cl

1. Basic oxides and hydroxides: Na₂O, NaOH, MgO and Mg(OH)₂	Links
Sodium oxide: Na₂O (s) + H₂O (l) " 2NaOH (aq) Na⁺(aq) + OH ^- (aq) + H⁺(aq) " Na⁺(aq) + H₂O (l) Magnesium oxide: MgO (s) + 2H⁺ (aq) " Mg²⁺ (aq) + H₂O (l) Mg(OH)₂ (s) + 2H⁺ (aq) " Mg²⁺ (aq) + 2H₂O (l)	Inorganic catalogue contents Basic oxides Amphoteric oxide Acidic oxides
2. Amphoteric oxide and hydroxide: Al₂O₃, Al(OH)₃.
Basic properties: Aluminium oxide is very resistant to attack by acids and so the first reaction is slow. Aluminium hydroxide reacts easily with dilute acids. Al₂O₃ (s) + 6H⁺ (aq) " 2Al³⁺ (aq)+3H₂O(l) Al(OH)₃ (s) + 3H⁺ (aq) " Al³⁺ (aq) + 3H₂O (l) Acidic properties: Alkaline attack on aluminium oxide is slow unless the alkali is hot and concentrated or molten. The formula of the aluminate ion shown is accepted in exams; you may also see [Al(OH)₄]^- or AlO₂^-, though the latter only really comes from reaction with molten alkali. Al₂O₃(s) + 6OH^–(aq) + 3H₂O(l) " 2 [Al(OH)₆]^{3 –}(aq) Aluminium hydroxide reacts readily with sodium hydroxide solution: Al(OH)₃ (s) + 3OH^–(aq) " [Al(OH)₆]^{3 –}(aq)
3. Acidic oxides (acid anhydrides) SiO₂, P₄O₁₀, SO₂, SO₃, Cl₂O.
Silicon dioxide, silica. Silica’s giant covalent lattice means it is very resistant to attack; the alkali solution must be concentrated and needs heating. SiO₂ (s) + 2 OH^–(aq) " SiO₃^{2 –}(aq) + H₂O(l) Phosphorus(V) oxide. The reaction is violent with cold water. P₄O₁₀ (s) + 2H₂O (l) " 4HPO₃(aq) On heating the solution further reaction occurs forming phosphoric(V) acid: HPO₃(aq) + H₂O(l) " H₃PO₄(aq) Sulphur dioxide: SO₂(g) + H₂O (l) " H₂SO₃ (aq) Sulphur trioxide: This reaction is violent, and is not used directly to make sulphuric acid. SO₃(g) + H₂O (l) " H₂SO₄ (aq) Dichlorine oxide: Cl₂O (aq) + H₂O(l) " 2 HClO (aq)