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MHTCET 25 Apr 2025 Shift 1 Paper

Question : 75 of 150

Marks: +1, -0

Calculate the value of dissociation constant of weak acid, which dissociates to 0.01\% in its 0.1 M solution?

Solution:

Concept:

For a weak acid, the dissociation constant is given by

K_a = C \alpha^2

, where

C

is the concentration and

\alpha

is the degree of dissociation.

Explanation:

The degree of dissociation is

\alpha = 0.01\% = \frac{0.01}{100} = 1 \times 10^{-4}

The concentration is

C = 0.1\ \mathrm{M}

Using the relation

K_a = C \alpha^2

K_a = 0.1 \times \left(1 \times 10^{-4}\right)^2

K_a = 0.1 \times 10^{-8} = 1 \times 10^{-9}

Answer:

K_a = 10^{-9}

Therefore, the correct option is D.

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