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Question: Answered & Verified by Expert
In a $0.2 \mathrm{M}$ aqueous solution, lactic acid is $6.9 \%$ dissociated. The value of dissociation constant is
ChemistryIonic EquilibriumCOMEDKCOMEDK 2023
Options:
  • A $1.2 \times 10^{-4}$
  • B $95 \times 10^{-4}$
  • C $6.5 \times 10^{-4}$
  • D $3.6 \times 10^{-2}$
Solution:
2765 Upvotes Verified Answer
The correct answer is: $95 \times 10^{-4}$
Given, $\alpha=6.9 \%$
$\therefore$ Degree of dissociation, $\alpha=\frac{6.9}{100}$
$\therefore \quad \alpha=0.069$
According to ostwald's dilution law,
$\begin{aligned}
& K_a=\alpha^2 C=(0.069)^2 \times 0.2 \\
& K_a=9.5 \times 10^{-4}
\end{aligned}$

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