STRENGTH OF ACID AND BASE
The strength of acid and base means the extend to which they provide H+ or OH- ions in aqueous solution, Greater the ability of acid and base to produce H+ or OH- ions respectively in aqueous solution greater will be their strength.
The strength of acid and base can be determined by degree of ionization. Greater the value of α greater will be strength of acid and base
α = No of dissociated molecules /Total Molecules
Following are the type of acid and base with respect to strength.
An acid produces H+ in aqueous solution in large extent is called strong acid. The value of degree of ionization for strong acid is high e.g. HCl, HNO3 etc.
An acid produces H+ in aqueous solution is small extent is called weak acid. The value of degree of ionization for weak acid is low e.g. CH3COOH, HCO3 etc.
All those base produce OH’ ion in aqueous solution is high extent are called strong base. The value of degree of ionization for strong base is high e.g. NaOH, KOH etc.
All those base produce 0H` ions in aqueous solution in low extent are called weak base. The value of degree of ionization for weak base is low e.g. NH4OH, Fe(OH)3
DISSOCIATION CONSTANT FOR ACID:
The strength of any acid can also be determined by dissociation constant; Greater the value of dissociation constant greater will be the strength of acid considers the e.g.
HCI + H20 <====> H3O+ + Cl-
Kc = [H3O][[CL] / [HCL]
Kc x [HCL] = [H3O][[CL]
Kc x [HCL] = constant = ka
Ka = [H3O][[CL]
Here Ka is called dissociation constant for acid.