Question

Explain bronsted ,arrhenius,and lewis theory of acid and base

Answer 1

ARRHENIUS ACID BASE THEORY:

An acid is substance which disassociate in aqueous solution to give hydrogen ions (H+)and base is the substance which dissociated to give hydroxyl ions(OH-).


LIMITATIONS OF ARRHENIUS ACID-BASE THEORY:

1) It is applicable to only aqueous solution .
2) It falied to explain acidic nature of substance s like SO2, CO2 etc,.. which doesn't possess a hydrogen.
3) It also falied to explain the basic nature of substances like NH3, Na2O, etc,...which doesn't possess a hydroxyl group


BRONSTED-LOWRY ACID-BASE THEORY:
An acid is a substance which donate proton (H+) while a base is a substance which accept a proton (H+).


Conjugate acid base pair:
The acid base pairs which differs by only one proton (H+) is called conjugate acid base pair.
For example 1) HCl conjugate base is Cl-
and Cl- conjugate acid is HCl
2) H2O conjugate base is OH-
and OH- conjugate acid is H2O

If acid is strong then its conjugate base is weak and vice versa.

LIMITATIONS OF BRONSTED-LOWRY ACID-BASE THEORY:
1) It didn't explain the strength of acids and bases
2) It can't be determine independently. It can only determined in presence of other substance
3) It doesn't explain the electron deficiency of BF3, BCl3, AlCl3.


LEWIS ACID-BASE THEORY:
An acid is substance which accept a pair of electrons while base is a substance which donates a pair of electrons.

LEWIS ACIDS:
1) simple cations. ex H+
2) molecules in which central atom is incomplete octet. ex BCL3, AlCl3, FeCl3
3) molecules in which central atom has empty d orbitals. ex SiF4, SnCL4, SF4
4) molecules having multiple bonds. ex CO2, SO2

LEWIS BASES:
1) all simple anions. ex Cl- , OH-, CN-
2) neutral species having at least one lone pair of electrons. ex NH3, etc.....

LIMITATIONS OF LEWIS ACID-BASE THEORY:
It cannot explain the strength of acids and bases.



HOPE YOU UNDERSTAND .....