Bronsted – Lowry Concept

To overcome the limitations of Arrhenius Concept of Acid and Base, Bronsted -Lowrey gave their concepts of acid and base called Bronsted- Lowry concept.

Bronsted- Lowry concept: According to this concept, an acid is a substance which can donate a proton during chemical reaction and a base is a substance which can accept a proton during a chemical reaction.

$$\ce{$\underset{\text{Bronsted Acid}}{\ce{HCl}}$ + $\underset{\text{Base}}{\ce{NH3}}$ ->NH4+ + Cl^-}$$

In the above given example, HCL has donated proton H+. So it is a bronsted acid and NH3 has accepted protons. So, it is a bronsted base.

In short:  An acid -base is just a transfer of proton from acid to base.  When acid donates proton it becomes base and when a base accepts proton, it becomes base.

Conjugate acid-base pair:

In acid base reaction, the two species which differs from each other by a proton is called conjugate acid and base pair. It is called neutralization reaction in terms of Bronsted-Lowry concept. For example:

$$\ce{$\underset{\text{Acid}}{\ce{H2O}}$ + $\underset{\text{Base}}{\ce{NH3}}$ ->$\underset{\text{Conjugate acid}}{\ce{NH4+}}$ + $\underset{\text{Conjugate base}}{\ce{OH-}}$}$$

 

 Merits of Bronsted-Lowry Concept:

  1. This concept is able to explain the basicity of NH3.
  2. It could explain the amphoteric nature of water.
  3. This concept can explain the amphiprotic nature of HCO3and other similar compounds.
  4. This concept is able to classify the acids as monoprotic, diprotic, polyprotic etc.

Limitations of Bronsted-Lowery Concept:

  1. It cannot explain the acidic nature of non metallic oxide like CO2, SO3 etc.
  2. It cannot explain the acidic nature of compounds like BF3, AlCl3 etc.
  3. It cannot explain the neutralization of NaOH with HCL to give NaCl and water since no conjugate acid base is formed here.

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