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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.
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.
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
C = concentration or moles of an electrolyte
V = dilution
For a weak base kb = a 2C
\ a =
or a =
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-]
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
pOH = The negative
logarithm, to the base 10, of the hydroxyl ion concentration is known as pOH of a solution.
- log[OH-] = log10
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