Question

All alkalies are bases, but all bases are not alkalies. Explain.

Answer 1

Alkali: A base that is soluble in water is called an alkali.

Base: A base is a substance that neutralizes acids by reacting with them. Some bases are water-soluble, while others are insoluble. Soluble bases are called alkalies. For example, copper oxide does not dissolve in water. Hence it is called a base.

Metals hydroxides are considered alkalis when they contain hydroxides of alkali metals and alkaline earth.
Example:
$\underset{\left(\mathrm{Potassium}\mathrm{hydroxide}\right)}{\mathrm{KOH}\left(\mathrm{aq}\right)}\to {\mathrm{K}}^{+}\left(\mathrm{aq}\right)+{\mathrm{OH}}^{-}\left(\mathrm{aq}\right)$
$\underset{\left(\mathrm{Calcium}\mathrm{hydroxide}\right)}{\mathrm{Ca}{\left(\mathrm{OH}\right)}_2\left(\mathrm{aq}\right)}\to {\mathrm{Ca}}^{+2}\left(\mathrm{aq}\right)+{\mathrm{OH}}^{-}\left(\mathrm{aq}\right)$

Hence, it is said that all alkalis are bases, but all bases are not alkalies.