A base is a substance that can neutralize an acid.

An alkali is a soluble base. eg. Sodium hydroxide

Alkali solutions are caustic(‘burn’) and contain  high concentrations of hydroxide ions, OH.eg. NaOH

Many bases have a low solubility and produce low concentrations of hydroxide ions. eg. Al(OH)3

These can be safely used as antacids to neutralize excess acid in the stomach and to prevent 'heart burn'

 

Gaviscon is mainly composed of aluminum hydroxide.

 

Hydroxides of the Periodic Table

Period

Group I

Group II

Group III

Formula

Solubility

pH*

Formula

Solubility

pH*

 

1

LiOH

13

> 14

Be(OH)2

0.001

9.7

 

Al(OH)3
 

Sol = 1 x 10-4
 

pH* = 7

2

NaOH

114

> 14

Mg(OH)2

0.0012

10.6

3

KOH

119

> 14

Ca(OH)2

0.18

12.5

4

RBOH

178

> 14

Sr(OH)2

0.8

12.9

5

CsOH

320

> 14

Ba(OH)2

4.7

13.5

Solubility is per 100 g of water at 25°C and pH* is of a saturated solution

Key trends

  • The solubility of metal hydroxides decreases across a period or row.
  • The solubility of metal hydroxides increases down a group or column.
  • The most soluble metal hydroxides belong to Group I, the alkali metals.
  • The strongest bases are in Group I because of their high solubility,

Concentrated soluble base solutions decompose protein such as skin, flesh and hair. They also decompose fats. These solutions are said to be caustic which means burn.

How are alkali solutions made?

Alkali solutions are made by adding soluble metal oxides to water.

Sodium oxide + water → Sodium hydroxide
Na2O + H2O → 2NaOH

 

 

Molar Mass
 

Formula Calculator