A level Chemistry AQA - Period 3

Sodium + water reaction

2Na + 2H₂O → 2NaOH + H₂

Sodium + water observations

Effervescence, Na floats on water, Na moves around on the surface of water, Na melts and forms ball, Na eventually disappears, solution remains colourless

Magnesium + water (l) reaction

Mg + 2H₂O (l) → Mg(OH)₂ + H₂

Magnesium + water (g)

Mg + H₂O (g) → MgO + H₂

Magnesium + water (g) observations

Mg burns with bright white light, white solid forms

Na₂O properties

Basic, ionic, high melting point

Na₂O formation observations

yellow flame, white solid formed, Na reacts spontaneous when exposed to air

sodium oxide + water reaction

Na₂O + H₂O → 2NaOH

sodium oxide + acid reaction

Na₂O + acid → Na salt + H₂O

MgO properties

basic, ionic, higher melting point that Na₂O

MgO formation observations

Bright which light, white solid forms

magnesium oxide + water reaction

MgO + H₂O → Mg(OH)₂

Why is the enthalpy of solution of MgO not in data book?

Because MgO is only sparingly soluble in water

magnesium oxide + acid reaction

MgO + acid → Mg salt + H₂O

Al₂O₃ properties

Amphoteric, ionic, high melting point

Why does Al₂O₃ not react with water?

Because it is insoluble

aluminium oxide + acid reaction

Al₂O₃ + 6H⁺ → 2Al³⁺ + 3H₂O

aluminium oxide + base reaction

Al₂O₃ + 2OH^- + 3H₂O → 2Al(OH)₄^-

amphoteric definition

reacts with both acids and bases

SiO₂ properties

acidic, giant covalent, very high melting point

silicon dioxide + base reaction

SiO₂ + 2OH^- → SiO₃^2- + H₂O

P₄O₁₀ properties

acidic, simple covalent, lower melting point than other P3 oxides

P₄O₁₀ formation observations

burns with bright white light, white smoke

phosphorus (V) oxide + water reaction

P₄O₁₀ + 6H₂O → 4H₃PO₄

phosphorus (V) oxide + base reaction

P₄O₁₀ + 12OH^- → 4PO₄^3- + 6H₂O

phosphorus (V) oxide + basic metal oxide

eg. 6Na₂O + P₄O₁₀ → 4Na₃PO₄

phosphoric acid + basic metal oxide

eg. 3MgO + 2H₃PO₄ → Mg₃(PO₄)₂ + 3H₂O

oxides of sulfur properties

acidic, simple molecular, low melting points

SO₂ properties

colourless gas, pungent smell, polar

SO₃ properties

colourless liquid, non-polar

SO₂ formation observations

burns with blue flame, misty white fumes, pungent smell

sulfur dioxide + water reaction

SO₂ + H₂O <> H₂SO₃

sulfur trioxide + water reaction

SO₃ + H₂O → H₂SO₄

Why does MgO have a higher boiling point that Na₂O?

Mg²⁺ ions are smaller and have a higher charge density so stronger electrostatic attraction between oppositely charged ions

Why does Al₂O₃ have a lower melting point than MgO?

Al₂O₃ has a higher degree of covalent character

Why does SiO₂ have the highest melting point?

Giant covalent lattice structure, many strong covalent bonds

Why does P₄O₁₀ have a higher melting point that SO₃?

larger Mr, more electrons, stronger van der Waals forces between molecules

phosphoric acid use

to acidify foods and drinks

phosphoric acid shape and bond angle

tetrahedral - 109.5

Sulphurous acid shape and bond angle

pyramidal - 107.5

Sulfuric acid shape and bond angle

tetrahedral - 109.5