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If pKb for fluoride ion at 25 ^(@) C ...

If `pK_b` for fluoride ion at ` 25 ^(@) C ` is 10.83 the ionisation constant of hydrofluoric acid in water at this temperature is

A

`1.74 xx 10^(-5)`

B

`3.52 xx 10^(-3)`

C

`6.75 xx 10^(-4)`

D

`5.38 xx 10^(-2)`

Text Solution

Verified by Experts

The correct Answer is:
C
The dissociation constants of weak acid and its conjugate base are related by an expression.
`pK_(a) + pK_(a) - pK_(w)` i.e. `pK_(a) +10.83 = 14`
or `pK_(a) = 14 - 10.83 = 3.17`
or `K_(a) = "Antilog" (-3.17) = 6.76 xx 10^(-4)`
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