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12.7 Ostwald’s Dilution Law
Ostwald’s dilution law is a relationship between the dissociation
constant and the degree of dissociation of a weak electrolyte (acids,
bases)
But concentration C = 1/v
for a weak electrolyte a
is very small ( and the law does not apply to strong electrolytes)
\ K
= a2C
For a weak acid a
= 
and a weak base a =
Examples : 1) The dissociation constant
of a weak electrolyte is 4 +10-
5 Calculate the degree of dissociation in 0.1
m solution.
2) Calculate the [H+]
and degree of dissociation in 0.5 m solution of acetic acid (Ka
= 1.8´ 10-
5)
\ a
= 6 ´
10- 3
\a =
6 ´ 10-
3
Now [H+]
= a C =
6 ´ 10-
3
´ 0.5
= 3 ´
10- 3 m
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