Arrhenius Concept of Acids and Bases
According to Arrhenius concept (1787):
Acid is a substance which dissociates in aqueous solution to give hydrogen ions.
For example, substances such as HCl, HNO3 , CH3 COOH, HCN, etc., are acids because they ionize in aqueous solutions to provide H+ ions.
H2SO4 + H2O H3O+ + HSO4–
HCl —water→ H+ + Cl–
On the other hand, base is a substance which dissociates in aqueous solution to give hydroxide ions.
The substances such as NaOH, KOH, NH4 OH, Ca(OH)2 etc. are bases because these compounds ionize in aqueous solutions to provide OH ions.
NaOH > Na+ + OH‾
Ca(OH)2 ==> CaO + H2O
Thus, according to Arrhenius Concept:
Acids give H+ ions in water, bases give OH– ions in water.
Examples of some important acids and bases are given in Table.
Table : Acids and Bases :
Limitation of Arrhenius concept:
- This concept is applicable only in aqueous medium and does not explain nature of acids and bases in non-aqueous medium.
- According to this concept, acids and bases are only those compounds which contain hydrogen (H+) and hydroxyl or hydroxide (OH–) ions, respectively. It can’t explain the nature of compounds like CO2, NH3, etc. which are acid and base, respectively.
Although this concept has limited scope yet, it led to the development of more general theories of acid-base behavior.