MHT-CET : Chemistry Entrance Exam

### MHT - CET : Chemistry - Ionic Equilibria Page 2

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9.

Dissociation Constant for a Weak Acid and Weak Base

Weak acid Ratio of concentration of cation (H+) and anion (A-) at equilibrium with concentration of undissociated acid at equilibrium.

HA H+ + A-

ka =

 [H+] [A- ] HA

Weak base Kb is the ratio of product of concentration of cation and the anion (
OH-) formed at equilibrium and concentration of undissociated base at equilibrium.

BOH B+ + OH-

kb =

 [B+] [OH- ] [BOH]

10.

Ostwald's Dilution Law

The degree of dissociation (a) of a given weak electrolyte is inversely proportional to the square root of concentration of solution or directly proportional to the square root of dilution.

a =

 where C = concentration or moles of an electrolyte V = dilution

For a weak base kb = a 2C

 \ a = or a =

 11. Ionic Product of Water The product of the ionic concentration of hydrogen ions and hydroxide ions in pure water or in any aqueous solution is called ionic product of water. It is constant at any given temperature. At 298K it is 1.0 × 10-14 Ionic product of water is Kw = [H+] [OH-]

12.

Hydrogen Ion Concentration pH Scale

pH The negative logarithm, to the base 10, of the hydrogen ion concentration is known as the pH of a solution.

- log[H+] = log10

 1 H +

= pH

pOH = The negative logarithm, to the base 10, of the hydroxyl ion concentration is known as pOH of a solution.

- log[OH-] = log10

 1 OH -

= pOH

 13. Relation Between pH and pOH [H+] [OH-] = Kw = 10-14 at 298 K This is according to ionic product of water simplifying pH + pOH = pKw = 14 at 298 K

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