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  • If pKb for fluoride ion at 25o C is 10.83, the ionisation constant of hydrofluoric acid in water at this temperature is:Opti

If pKb for fluoride ion at 25o C is 10.83, the ionisation constant of hydrofluoric acid in water at this temperature is:

Option: 1

3.52 x 10-3


Option: 2

1.74 x 10-5


Option: 3

8.75 x 10-4


Option: 4

6.75 x 10-4 


Answers (1)

best_answer

\begin{array}{l}{\text { The dissociation constants of weak acid and its conjugate }} \\ {\text { base are related by an expression. }} \\ {\mathrm{{\: \: p} K_{a}}+\mathrm{p K_{b}}=\mathrm{p K_{w}}} \\ {\text { i.e. } \mathrm{p K_{a}}+10.83=14} \\ {\text { or } \mathrm{p K_{a}=14-10.83=3.17}} \\ {\text { or } \mathrm{K_{a}}=\text { antilog }(-3.17)=6.76 \times 10^{-4}}\end{array}

Therefore, option(4) is correct

Posted by

Suraj Bhandari

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