Generally, metals or metal-like reactive radical oxides and hydroxides that undergo reaction with acid and produces salt and water are called bases. Examples:
Apart from CaO and KOH, examples of base are sodium oxide (NaO), sodium hydroxide (NaOH), copper oxide (CuO), ferrous oxide (FeO), calcium hydroxide [Ca(OH)2], ferrous hydroxide [Fe(OH)2], ammonium hydroxide (NH4OH) etc.
Ammonium ion (NH4+), phosphonium ion (PH4+) etc. radicals are reactive like metals. Metallic ions like Na+, K+ etc. get combined with non-metallic ions like Cl–, SO42- to produce ionic compounds like NaCl, KCl, Na2SO4, K2SO4 etc. Similarly, (NH4+), (PH4+) ions combined with Cl–, SO42- ions produce ionic compounds NH4C1, PH4Cl, (NH4)2SO4, (PH4)2 SO4.
Hence, the reaction between acid and base that produces salt and water is called acid-base neutralizing reaction. Therefore, it is said that acid neutralizes base and base neutralizes an acid.
Hydroxide compounds of metals or metal-like reactive radicals that are soluble in water are called alkali. A compound will be an alkali if (i) it contains hydroxide (OH–) radical and (ii) it dissolves in water. NaOH is an alkali as it has OH– radical and it dissolves in water. Whereas, Fc(OH)2 cannot be called an alkali for although it has OH’ radical, it does not dissolve in water. It is a base only. CaO is base but not an alkali as it does not contain OH– radical.
So, we get the bases containing OH– radicals and soluble in water are alkali. Thus it can be said In this way, ‘all bases are not alkali but all alkalis are bases’.
There are many basic compounds used in our household. The toilet cleaners in our houses containing sodium hydroxide (NaOH) and the glass cleaners containing ammonium hydroxide (NH4OH) are bases.