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10.3Period 3 Oxides

10.3    Period 3 Oxides

Summary of  the properties of  Period 3 oxides.

Reaction with water, H2O

  • Sodium oxide reacts exothermically with cold water to form sodium A strongly alkaline solution of sodium hydroxide is produced.

Na2O(s) + H2O(l) → 2NaOH(aq)     ; pH = 13

 

  • Magnesium oxide reacts slightly with water to the extent that it is almost insoluble. A weakly alkaline solution of magnesium hydroxide is produced

MgO(s) + H2O(l) → Mg(OH)2(aq)    ; pH = 9

 

  • Aluminium oxide does not react or dissolve in water due to its high lattice energy

 

  • Silicon dioxide does not react or dissolve in water due to the strong covalent bonds

 

  • Phosphorus oxides react with water to form acidic solutions(pH = 2).

Phosphorus(III) oxide reacts with water to form phosphorous acid.

P4O6(s) + 6H2O(l) → 4H3PO3(aq)

Phosphorus(V) oxide reacts with water to form phosphoric(V) acid.

P4O10(s) + 6H2O(l) → 4H3PO4(aq)

 

  • Sulfur oxides react with water to form acidic solutions(pH = 2).

Sulfur dioxide reacts with water to give sulfurous acid or sulfuric(IV) acid.

SO2(g) + H2O(l) → H2SO3(aq)

Sulfur trioxide reacts violently with water to form a mist of sulfuric acid.

SO3(g) + H2O(l) → H2SO4(aq)

 

Acid-base behaviour of  Period 3 oxides

  • Going across Period 3, the nature of the oxide changes from basic(Na2O, MgO) to amphoteric(Al2O3) then to acidic(SiO2, P4O6/P4O10, SO2/SO3). The acidity of the oxides increases across the Period
  • Sodium and magnesium oxides are basic oxides, they react with acid to give the corresponding salts and water.

Na2O(s) + 2HCl(aq) → 2NaCl(aq) + H2O(l) MgO(s) + 2HCl(aq) → MgCl2(aq) + H2O(l)

 

  • Aluminium oxide is amphoteric, it can react with both acid and base. Aluminium oxide reacts with hot and concentrated acids to give salt and water water

Al2O3(s) + 6HCl(aq) → 2AlCl3(aq) + 3H2O(l)

Aluminium oxide reacts with hot and concentrated sodium hydroxide to give sodium aluminate.

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

                                                                                                                                                                  sodium aluminate

  • Silicon dioxide is an acidic oxide, it reacts with hot and concentrated sodium hydroxide to give a colourless solution of sodium silicate

SiO2(s) + 2NaOH(aq) → Na2SiO3(aq) + H2O(l)

sodium silicate

  • Phosphorus oxides are acidic oxides, they react with alkalis to form salts and water

Phosphorus(III) oxide reacts with sodium hydroxide to form sodium phosphate(III) and water.

P4O6(s) + 12NaOH(aq) → 4Na3PO3(aq) + 6H2O(l)

Phosphorus(V) oxide reacts with sodium hydroxide to form sodium phosphate(V) and water.

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

 

  • Sulfur oxides are acidic oxides, they react with alkalis to form salt and Sulfur dioxide reacts with sodium hydroxide to form sodium sulfate(IV) and water.

SO2(g) + 2NaOH(aq) → Na2SO3(aq) + H2O(l)

Sulfur trioxide reacts with sodium hydroxide to form sodium sulfate(VI) and water.

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