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Arrhenius and Bronsted-Lowry Theory

Introduction:

Acids and bases are the first things which come into our mind on hearing the subject chemistry. Arrhenius and Bronsted, both are very well known scientists in the field of Chemical science. These two developed their own theories and concepts in defining acids and bases. Now, in chemistry, the definition of acids and bases and the relationship between them are taken into account from the theories given by these scientists.

Arrhenius theory:

In Arrhenius theory, the acid base interactions are based on the dissociation of ions in an aqueous solution.

According to this theory

  • Acids are the substances which give rise to hydrogen ions or protons in a solution. Let us consider a simple example:

When the aqueous solution of Hydrochloric acid is made, HCl dissociates into its constituent ions H+ and Cl- ions.  Hydrogen chloride ionizes in water to give hydrogen (H+).

  • Bases are the substances that give rise to hydroxide ions in a solution. Consider the given example:

In water, Sodium hydroxide dissociates to form its constituents ions, Na+ and OH- ions.

Limitations:

  • Acids and bases can be described only in the cases of aqueous solutions.
  • The nature of non-metal oxides cannot be explained by this theory.
  • Non-aqueous solutions containing acids and bases cannot be described by this theory.

Bronsted- Lowry theory

In Bronsted- Lowry theory, the acid base interactions are based on the proton transfer of the chemical compounds.

According to this theory:

  • An acid is a substance which donates protons.
  • A base is a substance which accepts protons.

In the above reaction between hydrochloric acid and water, the hydronium and chloride ions are formed. There is a proton transfer between hydrochloric acid and water to form the hydronium ion and loses a proton to form chloride ion.

Limitations

  • The acidic and basic nature of the organic compounds cannot be determined.
  • The reaction taking place in non-protonic solvents cannot be explained.
  • Substances like boron trifluoride and aluminium chloride do not contain protons but are known to act as acids. The explanation for this is not justified.

Differences:

Theory Acid Base Example
Arrhenious Acids are the substances which give rise to hydrogen ions or protons in a solution. In other word, acids are the substances which contain hydrogen. Bases are the substances that give rise to hydroxide ions in a solution.
Bronsted Acids are considered as proton donors. Bases are considered as proton acceptors.

There is another theory on acid, base concept. It is called the Lewis theory. According to Lewis concept acids are electron pair acceptors and bases are electron pair donors.

Frequently Asked Questions:

  1. Define acids and bases based on Arrhenius concept with an example.

Answer

  • Acids are the substances which give rise to hydrogen ions or protons in a solution. Let us consider a simple example:

 Hydrogen chloride ionizes in water to give hydrogen (H+).

  • Bases are the substances that give rise to hydroxide ions in a solution. Consider the given example:

In water, Sodium hydroxide dissociates to form its constituents ions, Na+ and OH- ions.

  1. Define acids and bases based on the Bronsted Lowry concept.

Answer

  • An acid is a substance which donates protons.
  • A base is a substance which accepts protons.

In the above reaction there is a proton transfer between hydrochloric acid and water to form the hydronium ion and loses a proton to form chloride ion.

  1. Highlight the limitations of Arrhenious and Bronsted Lowry theories.

Limitations of Arrhenious concept:

  • Acids and bases can be described only in the cases of aqueous solutions.
  • The nature of non-metal oxides cannot be explained by this theory.
  • Non-aqueous solutions containing acids and bases cannot be described by this theory.

Limitations of Bronsted Lowry concept:

  • The acidic and basic nature of the organic compounds cannot be determined.
  • The reaction taking place in non protonic solvents cannot be explained.
  • Substances like boron trifluoride and aluminium chloride do not contain protons but are known to act as acids. The explanation for this is not justified.

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