Question

Is $Mg{{\left( OH \right)}_{2}}$ alkali?

Answer 1

From the lower classes we are familiar with the word alkali. In chemistry the term alkali refers to the ionic salts of the alkali group elements or alkaline earth group elements and the salt will be basic in nature.

Complete step-by-step answer: $Mg{{\left( OH \right)}_{2}}$ is the hydroxide of Mg atom which is called magnesium hydroxide. Mg atom belongs to the second group of the periodic table i.e. to the alkaline earth metal group. We know that the alkali in chemistry refers to the basic ionic salt of the group 1 and group 2 elements i.e. the alkali and alkaline earth metals. Alkalis are those which dissolves in water and form a basic solution and will have a pH value greater than 7.
Now let us discuss magnesium hydroxide.$Mg{{\left( OH \right)}_{2}}$ is insoluble or more accurately it could be said as sparingly soluble in water. Only a very few parts of $Mg{{\left( OH \right)}_{2}}$ dissolve in water, but the dissolved part will undergo complete dissociation.
$Mg{{\left( OH \right)}_{2}}_{\left( s \right)}\rightleftharpoons M{{g}^{2+}}_{\left( aq \right)}+2O{{H}^{-}}_{\left( aq \right)}$
As the dissolved part undergoes complete dissociation as a strong electrolyte, $Mg{{\left( OH \right)}_{2}}$ can be considered as a strong electrolyte but the fact that it is sparingly soluble in water makes it less basic. Hence $Mg{{\left( OH \right)}_{2}}$ solution is a less basic solution.

Additional information:
The hydroxides of alkali and alkaline earth metals are strong bases, one of the best examples is NaOH.
Na is an alkali metal and the sodium hydroxide is one of the strongest bases. These solutions of salts of alkali and alkaline earth metals are strong bases as they have the ability to donate the electrons to the hydroxyl groups and get completely dissociated easily.

Note: Magnesium hydroxide is also called as the milk of magnesia and it is formed from the seawater by the addition of milk of lime i.e calcium hydroxide in larger quantities. And this alkali is used as the fire-retardant additive and as the main raw material for the production of magnesium metal.