Page 119 - Chemistry ICSE Class X
P. 119
Analytical Chemistry 105
Reaction of aluminium with boiling dilute NaOH and KOH
2Al(s) + 2NaOH(aq) + 2H O(l) o 2NaAlO (aq) + 3H (g)
2
2
2
dilute, boiling sodium aluminate
(soluble)
2Al(s) + 2KOH(aq) + 2H O(l) o 2KAlO (aq) + 3H (g)
2
2
2
dilute, boiling potassium aluminate
(soluble)
Action of Acids/Alkalis on Metal Oxides
Most metal oxides are basic in character. On dissolution in water, some of
such oxides form hydroxides (or alkalis). Such metal oxides and hydroxides
neutralise acids, but do not react with bases.
For example, sodium metal gives its oxide called sodium oxide (Na O).
2
Na O when dissolved in water gives NaOH (an alkali).
2
Both Na O and NaOH neutralise acids, such as hydrochloric acid,
2
sulphuric acid, acetic acid, etc.
'
4Na(s) + O (g) o 2Na O(s)
2
2
sodium oxygen sodium oxide
'
Na O(s) + H O(l) o 2NaOH(aq)
2
2
sodium hydroxide (alkali)
neutralisation
Na O(s) + 2HCl(aq) o 2NaCl(aq) + H O(l)
2
2
base acid salt water
neutralisation
NaOH(aq) + HCl(aq) o NaCl(aq) + H O(l)
2
base acid salt water
What are amphoteric oxides and hydroxides
The metal oxides and hydroxides which show both acidic as well as basic
character, i.e., which react with both acids and bases are called amphoteric
oxides and amphoteric hydroxides.
For example, oxides and hydroxides of zinc and aluminium are
amphoteric in character.
Amphoteric character of oxides of aluminium, zinc and lead
Basic character of aluminium oxide
Al O (s) + 6HCl(aq) o 2AlCl (aq) + 3H O(l)
3
2
2
3
aluminium oxide hydrochloric acid aluminium chloride water
Acidic character of aluminium oxide
Al O (s) + 6NaOH(aq) o 2NaAlO (aq) + H O(l)
2
2
2
3
aluminium oxide sodium hydroxide sodium aluminate water
Heat
Al O 3 + 2KOH o 2KAlO 2 + H O
2
2
aluminium oxide potassium hydroxide potassium aluminate water
Basic character of zinc oxide
ZnO(s) + H SO (dil.) o ZnSO (aq) + H O(l)
4
2
4
2
zinc oxide sulphuric acid zinc sulphate water
Acidic character of zinc oxide
ZnO(s) + 2NaOH(aq) o Na ZnO (aq) + H O(l)
2
2
2
zinc oxide sodium hydroxide sodium zincate water
ZnO + 2KOH o K ZnO 2 + H O
2
2
zinc oxide potassium hydroxide potassium zincate water
