Six Concept of Acid and Bases?

Six-Concept-of-Acid-and-Bases

Six CONCEPT OF ACID AND BASE:

There are six concept of acid and bases. We discuss one by one in the following.

THE ARRHENIUS  CONCEPT:-

 Define:

According to this an acid is defined as a hydrogen containing substance which gives H+ ion (H3O+) when dissolved in water.

*
A base is a substance which contains OH groups and gives hydroxyl ions OH- when dissolved in water.

FOR Example:

According to this an acid is defined as a hydrogen containing substance which gives H+ ion (H3O+) when dissolved in water.

*
A base is a substance which contains OH groups and gives hydroxyl ions OH- when dissolved in water.

FOR Example:

Hcl→H­­++Cl      
koh      →k+oH
Advantages.
This concept explain the constant heat of neutralization of any strong acid with any strong base as well these reaction involve only combination of hydrogen ion and hydroxyl ion.
One of the most significant achievement of these concept was its ability to explain catalytic properties of acid.

 THE PRO-TONIC OR BRONSTED CONCEPT:


ACCORDING TO BRONSTED:-

An acid is defined as a species (a compound or an ion ) which donates or tends to donate a proton (H+).
A base is defined an a species which accept  or tends to accept a proton.          
Six-Concept-of-Acid-and-Bases
                             Example
HCl + H2O H3O++cl
Ch3Cooh+NH3   →NH4+ch3coo
H2O+NH3→NH4+OH
Conjugate Acid And base Pairs.
In an acid-base reaction , an acid yields a base (conjugate) and base after accepting proton yields a conjugate acid.           
Every acid has a conjugate base and every base has a conjugate acid.
If acid is strong conjugate base is weak.
If base is strong conjugate acid is weak.
Amphortic Species
A species that act both as a proton doner and a proton accepter is said to be amphiprotic.
Examples
            HCl + H2O H3O+ +cl
            H2O+NH3→NH4+OH

THE LEWIS CONCEPT:-


According to Lewis” A acid is defined as a species (molecules or ion) which can accept a pair of electrons and a base is a species which can donates pair of electrons.
* An acid is an electrophile (electron loving)
*  Base is a nucleophile (nucleus loving)
* An acid base reaction involves donation of a pair of electrons from a base to an acid with coordinates bond between the two .                                                                                                                           Example.
H+NH3 →NH4
BF3+NH3→F3B    …….NH3
Alcl3+NH3→cl3AL…….NH3

Lewis Acids classification:

All sample cation are lewis acids molecules containg incomplete act are act as Lewis acids.
Lewis bases
It include all anions molecules having unshared electron act as  base.

THE LUX-FLOOD CONCEPT:-

The pro-tonic concept cannot be applied to the species having no protons, for example oxide system.
*According to the Lux-flood concept.
A base is defined as any species which gives up an oxide ion (o-2) and
An acid is defined as  any species which gains or takes up oxide ions.
     
Examples.
Cao+sio2→casio3
Bao+co2→baco3
Cna2o+p4o10→4Na3po4
Pbo+so3→pbso
Substance which show character of both acids and base is called amphoteric ex zno
zno→zno2

THE USANOVICH CONCEPT:-

According to this concept an acid is defined as any species,

(1) Which capable of giving cations

(2) Capable with combining with anions

(3) nutralizing a base to give  a salt.

*A base is defined as any species ,

(1) capable of giving up anions or electrons.

(2) combining with cations.

(3) neutralizing an acid to give a salt.                 

Examples
So3+Na2o→Na2so4
Cl2+2NA→2Nacl
HCl+NH3→NH­­4cl
NH4+OH→NH3+H2O

SHAB concept:

This concept explain acids and base in term of their relative strength.
Soft base:
According to this concept soft base is that in which donor atom is highly  polarize has has low electro negatively  easily oxidized valance electrons are loosely attached.
Examples
H. 
R
Hard base:-
In this case atom is of low polorizibility, high electronegative the valance orbital.
With high energy not easily oxizidezed and valance electron tightly bound
Example
NH3.    N2H4
Soft Acids.
The acceptor atom is of low positive charge large size end has serval outer electrom which can be easily oxidized
Example
Copper . mecury
Hard Acid
In these acceptor atom is high positive charge small size and not has outer electron which can be easily excited
Example H­­+ LI+ NA+ 

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About the Author: Waleed Ahmed

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