What are the limitations of Arrhenius definition?
Answers
Explanation:
Arrhenius theory is known to be the most limited of the three theories since it requires the solutions to be aqueous. It only applies to substances that produce Hydrogen ions (H+) or hydroxide ions (OH−).
1- An acid is expected to be an acid in any solvent. But that’s not the case nowadays. For example HCL acts as an Arrhenius acid when dissolved in water. However when HCL is dissolved in benzene there is no dissociation. This is against Arrhenius theory; Arrhenius states that dissociation occurs in any aqueous solution. The properties of acid and bases play a critical role.
2- Arrhenius did not explain in his theory the behavior of acids and bases in a non aqueous solution For example, the dissociation of acetic acid in methanol it could be written as CH3CO2H + CH3OH ⇄ CH3CO2− + CH3OH
3- In Arrhenius theory all salts should produce solutions that are neither acidic nor basic. But there are some exceptions against this theory. For example if equal amounts of HCl and ammonia react, the solution is slightly acidic. If equal amounts of acetic acid and sodium hydroxide react, the resulting solution is basic. Arrhenius theory does not include any explanation for this.
4- The need for hydroxide as the base led Arrhenius to propose the formula NH4OH as the formula for ammonia in water. This led to the misunderstanding that NH4OH is the actual base. But the actual base is NH3.
5- As you read before the bare proton H+, cannot exist for a long time in a water solution. Therefore this reaction: H2O + H+ à H3O+ Occurs most of the time