Introduction :
According to Arrhenius an acid is any substance that dissociates to give a H+ ion in aqueous solution.
Thus an aqueous solution of hydrochloric acid will show the presence of H+ ions and Cl- ions.
Later it was found that the H+ ions have no free existence in water or in aqueous solution but exist in the solvated state as hydronium ion as H3O+.
Thus according to Arrhenius definition of an acid, any substance that will increase the concentration of H+ ions in water is said to be an acid.
General Representation: An Arrhenius acid is generally represented by the formula with a H in the begining as HCl , H2SO4 , HNO3. All acids that can donate a proton in aqueous solution or can increase the concentration of H3O+ ions in solution are called Arrhenius acids.The dissociation of an acid in water can be represented by the equation a follows:
If HCl be the acid then the dissociation is given as
HCl((g) + H2O(l) ---> H3O+ + Cl-
1) All protic acids that can dissociate in aqueous solution to increase the H+ ione concentration show similar properties such as :
Reaction with bases result in neutralisation of the acid and formation of water and a salt
example: HCl + NaOH----------> NaCl + H2O
HNO3 + KOH --------> KNO3 + H2O
2) The basicity of the acids depends upon number of H+ ions, an acid can releas in aqueous solution
3) The pH of any substance depends upon the number of H+ ions the substance can release in solution
HCl (aq) ----------> H+(aq) + Cl- (aq)
H+ (aq) + H2O (l) ---------> H3O+ (aq)
But HCl in gaseous state is neither acidic nor basic.
2) Acid not dissolved in (aq) solution cannot dissociate into H+ ions. For example
HNO3 (l) + 2H2SO4 (l) -----------> NO++ (l) + H3O+ (l) + 2HSO4- (l)
Here HNO3 acts as a base
3) Arrhenius definition of acid cannot account for the acidic character of AlCl3
According to Arrhenius an acid is any substance that dissociates to give a H+ ion in aqueous solution.
Thus an aqueous solution of hydrochloric acid will show the presence of H+ ions and Cl- ions.
Later it was found that the H+ ions have no free existence in water or in aqueous solution but exist in the solvated state as hydronium ion as H3O+.
Thus according to Arrhenius definition of an acid, any substance that will increase the concentration of H+ ions in water is said to be an acid.
General Representation: An Arrhenius acid is generally represented by the formula with a H in the begining as HCl , H2SO4 , HNO3. All acids that can donate a proton in aqueous solution or can increase the concentration of H3O+ ions in solution are called Arrhenius acids.The dissociation of an acid in water can be represented by the equation a follows:
If HCl be the acid then the dissociation is given as
HCl((g) + H2O(l) ---> H3O+ + Cl-
The advantage of the Arrhenius definition of an acid.
1) All protic acids that can dissociate in aqueous solution to increase the H+ ione concentration show similar properties such as :
Reaction with bases result in neutralisation of the acid and formation of water and a salt
example: HCl + NaOH----------> NaCl + H2O
HNO3 + KOH --------> KNO3 + H2O
2) The basicity of the acids depends upon number of H+ ions, an acid can releas in aqueous solution
3) The pH of any substance depends upon the number of H+ ions the substance can release in solution
Limitation of Arrhenius definition of acid>
1) Arrhenius definition of acid holds good only for acids in aqueous solution. For exampleHCl (aq) ----------> H+(aq) + Cl- (aq)
H+ (aq) + H2O (l) ---------> H3O+ (aq)
But HCl in gaseous state is neither acidic nor basic.
2) Acid not dissolved in (aq) solution cannot dissociate into H+ ions. For example
HNO3 (l) + 2H2SO4 (l) -----------> NO++ (l) + H3O+ (l) + 2HSO4- (l)
Here HNO3 acts as a base
3) Arrhenius definition of acid cannot account for the acidic character of AlCl3
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