MCQ
If $p{K_b}$ for fluoride ion at ${25\,^o}C$ is $10.83$, the ionisation constant of hydrofluoric acid in water at this temperature is
  • A
    $1.74 \times {10^{ - 3}}$
  • B
    $3.52 \times 10^{-3}$
  • $6.75 \times {10^{ - 4}}$
  • D
    $5.38 \times {10^{ - 2}}$

Answer

Correct option: C.
$6.75 \times {10^{ - 4}}$
(c) ${K_a} \times {K_b} = {K_w}$

$\therefore \,{K_a} = \frac{{{K_w}}}{{{K_b}}}$$ = \frac{{{{10}^{ - 14}}}}{{1.48 \times {{10}^{ - 11}}}}$$ = 6.75 \times {10^{ - 4}}$

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