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The pH of a 0.1 molar solution of the ac...

The pH of a 0.1 molar solution of the acid HQ is 3. The value of the ionization constant, `K_(a)` of this acid is :

A

`1xx10^(-7)`

B

`3xx10^(-7)`

C

`1xx10^(-3)`

D

`1xx10^(-5)`

Text Solution

Verified by Experts

The correct Answer is:
D
`{:(,HQ,hArr,H^(+),+,Q^(-)),("Initial conc.",0.1,,0,,0):}`
If x is the degree of ionization
`0.1-x " " x " "x`
Now, pH = 3 or `[H^(+)]=10^(-3) therefore x=10^(-3)`
`K_(a)=(x xx x)/(0.1-x)=((10^(-3))^(2))/(0.1-10^(-3))`
Assuming `0.1-10^(-3)=0.1`
`K_(a)=((10^(-3))^(2))/(0.1)=1xx10^(-5)`
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