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What is an alkali? What is a base?

What is an alkali? What is a base?

A base is a compound that can neutralize an acid. An alkali is a soluble base which is very corrosive. Alkali solutions turn pink litmus paper blue.


Bases can be strong or weak. All bases can be used to neutralize an acid. The reaction between an acid and a base is called a neutralization reaction.

Acid + Base => Salt + Water

The products of a neutralization reaction are salt and water.


Strong bases are called alkalis. They are soluble in water and prdouce alkali solutions which are very corrosive like sodium hydroxide which is commonly called caustic soda. Alkalis are used to dissolve fats and are found in oven cleaning and general cleaning products.

Alkali Chemical formula
Lithium hydroxide LiOH
Sodium hydroxide NaOH
Potassium hydroxide KOH
Ammonia NH3

The elements of Group I of the Periodic tablle are called alkali metals as they all react with water producing alkali solutions.

Alkalis are soluble bases and produce solutions with a very high concentrations of hydroxide ions, OH-

sodium hydroxide => sodium ions + hydroxide ions

                 NaOH     =>    Na+ + OH-

    high solubility            high concentration of hydroxide ions, OH-

 The high concentration of hydroxide ions makes alkalis very caustic. The word caustic means 'burns'

The base ammonia, NH3 produces hydroxide ions as it dissolves in water.

Ammonia + water => ammonium ions + hydroxide ions

           NH3 + H2O => NH4+ + OH-


Weak bases have a very low solubility in water. They are non corrosive and react slowly with acids as they produce a low concentration of hydroxide ions in water.

Magnesium hydroxide => Magnesium ions + hydroxide ions

Mg(OH)2           =>    Mg2+ + 2OH-

low solubility          low concentration of hydroxide ions, OH-

The low concentration of hydroxide ions means they are safer to handle.

Some bases can be used as antacids to neutralize excess hydrochloric acid from the stomach. eg. magnesium hydroxide and aluminum hydroixde.

Acid +  Base => Salt + Water

Hydrochloric acid  + magnesium hydroxide => magnesium chloride + water

2HCl + Mg(OH)2 => MgCl2 + 2H2O