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Bronsted/Lowry theory

Bronsted Theory:

Bronsted/Lowry acid: Substance that donates proton [H
+].

Example: HCl, CH3COOH, H2CO3

Bronsted/Lowry base: Substance that accepts proton [H+].

Example: NH3, HCO3-, SO42-

Limitation:
1.  Theory is based on proton transfer but there are many other compounds which do not donates proton and acts as acid. There are many acid-base reactions where proton transfer is not involved.
  SO
2 + SO2
   →  SO2+ +SO32-

All Arrhenius acids and bases are Bronsted/Lowry acid and bases.

Water is having dual character as it accepts and donates proton. Such types of compounds are called as amphoteric compounds.

  H
2O + HCl
  →  H3O+ +Cl-……………………(1)
  H
2O + NH3
   →  NH3+ +OH-……………………(2)

In first reaction water accepts proton from HCl and act as a base whereas in second reaction it donates proton to ammonia and act as an acid.

When an acid transfers its proton it becomes the conjugate base (CB) and once a base accepts the proton it becomes the conjugate acid (CA). So, in first reaction Cl
- is conjugate base and H3O+ is conjugate acid.


Lewis Theory:

Lewis acid: Substance that accepts electron pair
Example: H+, NH4+, Na+

Lewis base: Substance that donates electron pair

Example: NH3, OH-, Cl-, CN-

Limitation:
1.  Theory is based on transfer of electron pair so reactions are expected to be very fast however there are many other acid-base reactions which are very slow.

All Bronsted/Lowry acids and bases are Lewis acids and bases.

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