[Inorganic] Period 3 Compounds

Ionic oxides and hydroxides

• Names

• Nature

Ionic oxides and hydroxides

• Names

• Nature

• Na₂O, NaOH, MgO, Mg(OH)₂

• Basic

Ionic oxides with covalent character

• Names

• Nature + reason

• Equations

• Al₂O₃, Al(OH)₃

• Amphoteric due to high charge density of Al3+ that polarises electron cloud of OH- or O2-, inducing covalent character

• Al₂O₃ (s) + NaOH (aq) + 3H2O (l) → 2NaAl(OH)₄ (aq)

• Al(OH)₃ (s) + 3NaOH (aq) → NaAl(OH)₄ (aq)

Covalent oxides and hydroxides

• Names

• Nature

• Equations

• SiO₂, P₄O₁₀, SO₃

• Acidic

• SiO₂ (s) + hot conc. 2NaOH (aq) → Na₂SiO₃ (aq) + H₂O(l) (due to strong and extensive covalent bonds between Si and O atoms in lattice structure)

• P₄O₁₀ (s) + 12NaOH (aq) → 4Na₃PO₄ (aq) + 6H₂O (l)

• SO₃ (g) + 2NaOH (aq) → Na₂SO₄ (aq) + H₂O (l)

Describe the reaction of Na₂O with water, including

• equation(s)

• final pH of solution and colour of UI

Reacts vigorously with cold water to form strongly basic solution

• Na₂O (s) + H₂O (l) → 2NaOH (aq)

• pH13, purple

Describe the reaction of MgO with water, including

• equation(s)

• final pH of solution and colour of UI

Reacts less vigorously to form a weakly alkaline solution due to highly exothermic lattice energy (charge density) and hence low solubility

• MgO (s) + H₂O (l) → Mg(OH)₂ (aq)

• pH9, blue

Describe the reaction of Al₂O₃ with water, including

• equation(s)

• final pH of solution and colour of UI

No reaction to very highly exothermic lattice energy and hence low solubility

• pH7, green

Describe the reaction of SiO₂ with water, including

• equation(s)

• final pH of solution and colour of UI

No reaction due to strong and extensive covalent bonds between Si and O atoms in lattice structure

• pH7, green

Describe the reaction of P₄O₁₀ with water, including

• equation(s)

• final pH of solution and colour of UI

Reacts vigorously to form an acidic solution

• P₄O₁₀ (s) + 6H₂O (l) → 4H₃PO₄ (aq)

• pH2, red

Describe the reaction of SO₃ with water, including

• equation(s)

• final pH of solution and colour of UI

Reacts vigorously to form an acidic solution

• SO₃ (s) + H₂O (l) → H₂SO₄ (aq)

• pH2, red

Describe the reaction of NaCl with water, including

• equation(s)

• nature of chloride

• final pH of solution and colour of UI

Dissolves/undergoes hydration to form a neutral solution

• NaCl (s) → Na+ (aq) + Cl- (aq)

• ionic chloride

• pH7, green

Describe the reaction of MgCl₂ with water, including

• equation(s)

• nature of chloride

• final pH of solution and colour of UI

Dissolves with partial hydrolysis to give a slightly acidic solution due to high charge density and polarising power, polarising the electron clouds of surrounding H₂O molecules, weakening O-H bonds in H₂O and resulting in the release of protons.

• MgCl₂ (s) + 6 H₂O (l) →[Mg(H₂O)₆]2+ (aq) + 2 Cl- (aq)

• [Mg(H₂O)₆]2+ (aq) + H₂O (l) ⇌ [Mg(H₂O)₅(OH)]+ (aq) H₃O+ (aq)

• ionic chloride

• pH6.5, yellow

Describe the reaction of AlCl₃ with water, including

• equation(s)

• nature of chloride

• final pH of solution and colour of UI

Dissolves with partial hydrolysis to give an acidic solution due to high charge density and polarising power, polarising the electron clouds of surrounding H2O molecules, weakening O-H bonds in H2O to a large extent, resulting in the release of protons.

• AlCl₃ (s) + 6 H₂O (l) →[Al(H₂O)₆]3+ (aq) + 3 Cl- (aq)

• [Al(H2O)₆]3+ (aq) + H₂O (l) ⇌ [Al(H₂O)₅(OH)]2+ (aq) H₃O+ (aq)

• covalent chloride with ionic character

• pH3, red

Describe the reaction of SiCl₄with water, including

• equation(s)

• nature of chloride

• final pH of solution and colour of UI

Undergoes complete hydrolysis due to low-lying d-orbital in central Si atom that accept a lone e- pair from H₂O. The formation of HCl which dissolves in water gives a strongly acidic solution.

• SiCl₄ (l) + 2 H₂O (l) → SiO₂ (s) + 4 HCl (aq)

• covalent chloride

• pH2, red

Describe the reaction of PCl₅ water, including

• equation(s)

• nature of chloride

• final pH of solution and colour of UI

Undergoes complete hydrolysis due to low-lying d-orbital in central P atom that accept a lone e- pair from H₂O. The formation of HCl which dissolves in water gives a strongly acidic solution.

• PCl₅ (s) + 4 H₂O (l) → H₃PO₄ (aq) + 5 HCl (aq)

• covalent chloride

• pH2, red

Explain the formation of white HCl fumes in the reaction between covalent chlorides and limited water (1:1), with the aid of equations.

Due to heat produced and high concentration of the solution formed, H+ and Cl- ions form HCl which is given off as a gas: PCl₅ (s) + H₂O (l) → POCl₃ (l) + 2 HCl (g)

In large access of water, the temperature will not be sufficiently larger and HCl will dissolve: POCl₃ (l) + 3 H₂O (l) → H₃PO₄ (aq) + 3 HCl (aq)