Question

(a) define a base.
(b) Explain, all alkalis are bases but all bases are not alkalis.

Answer 1

(a) Base is a compound that contains displaceable oxide (${\mathrm{O}}^{2-}$) or hydroxide (${\mathrm{OH}}^{-}$) ion or ions. A base reacts with ${\mathrm{H}}^{+}$ or ${\mathrm{H}}_3{\mathrm{O}}^{+}$ions (hydronium) present in an acid to produce a salt and water. Examples include NaOH and CuO.

$$\begin{gathered} \mathrm{NaOH}+\mathrm{HCl}\stackrel{}{\to }\mathrm{NaCl}+{\mathrm{H}}_2\mathrm{O} \\ \mathrm{Base}\mathrm{Acid}\mathrm{Salt}\mathrm{Water} \end{gathered}$$

(b) An alkali is a basic hydroxide that is soluble in water; it produces hydroxyl (${\mathrm{OH}}^{-}$) ions as the only negatively charged ions. Sodium hydroxide and calcium hydroxide are water-soluble bases; thus, they are alkalis. But all bases are not alkalis, as many bases do not dissolve in water.​ Bases like ferric hydroxide and cupric hydroxide are not soluble in water; hence, they are not alkalis. Thus, we can say that all alkalis are bases, but all bases are not alkalis.