inorganic - periodicity 2.2

Question 1

basic oxides

Answer 1

• sodium and magnesium oxides are both bases

Question 2

sodium oxide reacting with water

Answer 2

• sodium hydroxide solution given
• it is strongly alkaline - pH = 13-14
  Na2O(s) + H2O(l) –> 2Na+ (aq) + 2OH- (aq)

Question 3

magnesium oxide reacting with water

Answer 3

• magnesium hydroxide given - but it is sparingly soluble in water
• somewhat alkaline solution produced -
  pH = ~9
  MgO(s) + H2O –> Mg(OH)2(s) ⇌ Mg2+ (aq) + 2OH- (aq)

Question 4

insoluble oxides

Answer 4

• aluminium oxide

- sulphur dioxide

Question 5

acidic oxides

Answer 5

• phosphorus pentoxide
• sulphur dioxide
• sulphur trioxide

Question 6

phosphorus pentoxide reacting with water

Answer 6

• reacts violently
• acidic solution of phosphoric (V) acid produced
  P4O10(s) + 6H2O(l) –> 4H3PO4(aq)
• ionises:
  H3PO4(aq) ⇌ H+ (aq) + H2PO4- (aq)

Question 7

sulphur dioxide reacting with water

Answer 7

• fairly soluble in water
• acidic solution of sulphuric (IV) acid - or sulfurous acid - produced
  SO2(g) + H2O(l) –> H2SO3(aq)
  H2SO3(aq) ⇌ H+ (aq) + HSO3- (aq)

Question 8

sulphur trioxide reacting with water

Answer 8

• reacts violently with water
• acidic solution of sulphuric acid - sulphuric (VI) acid - produced
  SO3(g) + H2O(l) –> H2SO4(aq) –> H+(aq) + HSO4-(aq)

Question 9

sodium oxide behaviour

Answer 9

• sodium oxide contains the oxide ion O2-
• it strongly attracts protons
• therefore ready reacts with water to produce hydroxide ions
• strong alkaline solution

Question 10

magnesium oxide behaviour

Answer 10

• magnesium oxide contains the oxide ion
• however, it is less soluble than sodium
• its reaction with water produces a less alkaline solution because it does not readily react with water to produce a lot of hydroxide ions

Question 11

phosphorus oxide and sulphur oxides behaviour

Answer 11

• covalent molecules

- react with water to form acid solutions

Question 12

aluminium oxide behaviour

Answer 12

• bonding is too strong for ions to be separated - partly because of the additional covalent bond character

Question 13

silicon oxide behaviour

Answer 13

• giant macromolecule

- water does not affect this type of structure

Question 14

summary

Answer 14

• solutions go from alkaline to acidic across the period