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The degre of dissociation of weak electr...

The degre of dissociation of weak electrolyte is inversely proportional to the same square root of concentration. What is called Ostwald's dilution law.
`alpha = sqrt((K_(a))/(c ))` As the temperature increases, degree of dissociation will increase.
`(alpha_(1))/(alpha_(2)) = sqrt((K_(a1))/(K_(a2)))` if concentration is same. `(alpha_(1))/(alpha_(2)) = sqrt((c_(2))/(c_(1)))` if acid is sam.
pH of 0.005 M HCOOH `[K_(a) = 2 xx 10^(-4)]` is equal to : 3, 2, 4, 5

A

3

B

2

C

4

D

5

Text Solution

Verified by Experts

The correct Answer is:
A
pH of 0.005 M HCOOH : `K_(a) = 2 xx 10^(-4)`
Since C is low and `K_(a)` is high. Solve the quadratic equation.
`K_(a) = (C alpha^(2))/(1-alpha) rArr 2 xx 10^(-4) = ((0.004) alpha^(2))/(1-alpha) rArr alpha = 0.18 rArr pH - log C alpha = - log (0.005 xx 0.18) ~~3`
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