COH
O
CO−
O
R H
Stronger acid Weaker base
R + −O H + O H
Stronger base Weaker acid
pKa = 3-5 pKa = 15.7
Na+
Large difference in pKa value ⇒ the position of equilibrium will greatly favor
the formation of the products (one-way arrow is used)
- Water-insoluble carboxylic acids dissolve in aqueous sodium hydroxide:
COH+ +
O
CO−
O
−O H H O H
Insoluble in water Soluble in water
Na+ Na+
(Due to its polarity as a salt)
1) Carboxylic acids containing fewer than five carbon atoms are soluble in water.
- Amines react with hydrochloric acid:
+ RN+ +
H
Stronger acid
H
Weaker base
H O+ H
H
Cl H O H
Stronger base
NH 2
H
Weaker acid
pKa = 9-10
R − Cl−
pKa = -1.74
- Water-insoluble amines dissolve readily in hydrochloric acid:
+ C 6 H 5 N+ +
H
Water-insoluble
NH 2
H
H
Water-solublesalt
C 6 H 5 H O+ H
H
Cl− Cl− H O H
1) Amines of lower molecular weight are very soluble in water.
