Arrhenius Theory of Acids and Bases:
Based on his theory of electrolytic dissociation Arrhenius 1984 defined acids as those compounds which give H+ ions, in an aqueous solution and bases are those compounds which give OH– ions in an aqueous solution.
HCL (aq) ⇌ H
+ (aq) + Cl– (aq)
NaOH (aq) ⇌ Na
+ (aq) + OH– (aq)
Limitations of Arrhenius Theory:
1. According to Arrhenius’s theory, the entire acid-base phenomenon was confined to an aqueous medium only and the process of neutralization leading to the formation of salt and water could not take place in any other medium except water. But it is well known that neutralization can take place in many non-aqueous solvents and even in absence of solvents.
2. According to Arrhenius’s theory, only those compounds were regarded as bases which contain OH– ions, i.e, the basic character was confined to the hydroxides only and even the oxides of strongly electropositive metals were not regarded as bases.
3. There are several substances which don’t provide H+ ions and OH– ions but still behave as acids and bases.
4. Recent researchers reveal that H+ ions in acidic solution don’t exist as such but exist in combination with H2O molecule as hydronium ions.