Page 89 - Chemistry ICSE Class X

Study of Acids, Bases and Salts 75
Salts

What is a salt

The term salt is used for all ionic (or electrovalent) compounds made up of
+
positive ion (other than H ) derived from a base and a negative ion (other
–
than OH ) derived from an acid.
Salt is the product of the neutralisation reaction between an acid and
a base.
For example, sodium chloride formed in the reaction between sodium
hydroxide and hydrochloric acid is a salt.
NaOH(aq) + HCl(aq) o NaCl(aq) + H O
2
base acid salt (sodium chloride) water
NH OH(aq) + HCl(aq) o NH Cl(aq) + H O
2
4
4
base acid salt (ammonium chloride) water
In the above reactions, hydrogen ion of an acid is replaced by a metal ^ĂůƚƐ ĂƌĞ ĨŽƌŵĞĚ ďLJ ƚŚĞ ƌĞĂĐƟŽŶ
ion or ammonium ion. Thus, a UCNV OC[ CNUQ DG FGſPGF CU VJG EQORQWPF ďĞƚǁĞĞŶ ĂŶ ĂĐŝĚ ĂŶĚ Ă ďĂƐĞ͘
formed when the hydrogen ion of an acid is replaced by a metal ion or an
ammonium ion.

Classification of Salts

5CNVU ECP DG ENCUUKſGF KPVQ VJG HQNNQYKPI ECVGIQTKGU
ƒ Normal salts ƒ Acid salts
ƒ Basic salts ƒ Double salts
ƒ Mixed salts ƒ Complex salts

What are normal salts
When all the replaceable hydrogen atoms in an acid molecule are replaced
by metal ions, the salt formed is called normal salt.
Sodium chloride (NaCl), sodium sulphate (Na SO ), calcium carbonate
4
2
(CaCO ), sodium carbonate (Na CO ) are normal salts.
3
3
2
HCl(aq) + NaOH(aq) o NaCl(aq) + H O(l)
2
H SO (aq) + 2NaOH(aq) o Na SO (aq) + 2H O(l)
4
4
2
2
2
H SO (dil.) + Mg(s) o MgSO (aq) + H (g)
4
2
4
2
What are acid salts
The salt obtained by partial replacement of ionisable hydrogen atoms in an
acid molecule by metal ions is called an acid salt.
For example, the salts formed in the following reactions are acid salts.
H SO (aq) + NaOH(aq) o NaHSO (aq) + H O EĂ,^K ͕ EĂ, K ͕ EĂ, WK ĂŶĚ
2
2
4
4
sulphuric acid sodium hydroxide sodium hydrogensulphate 4 3 2 4
EĂ ,WK ĂƌĞ acid salts͘
4
2
H CO (aq) + NaOH(aq) o NaHCO (aq) + H O
3
3
2
2
carbonic acid sodium hydroxide sodium hydrogencarbonate
(or sodium bicarbonate)
H PO (aq) + NaOH(aq) o NaH PO (aq) + H O
2
2
4
3
4
phosphoric acid sodium hydroxide sodium dihydrogen phosphate
NaH PO (aq) + NaOH(aq) o Na HPO (aq) + H O
4
4
2
2
2
sodium dihydrogen sodium hydroxide disodium hydrogen
phosphate phosphate