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Question 600412
JEE Chemistry · Medium

Chemical and Ionic Equilibrium: Weak acid MCQ

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Weak acidMediumQuestion 600412

Question

For a weak acid HA with concentration C and Ka, the degree of dissociation α = √(Ka/C) when:
  1. A
    α is not small
  2. B
    α << 1 (small dissociation)
    Correct
  3. C
    C is very large
  4. D
    Ka > 1

Correct answer

α << 1 (small dissociation)

Explanation

For weak acid HA ⇌ H⁺ + A⁻: Ka = Cα²/(1−α) ≈ Cα² if α << 1. So α = √(Ka/C). This approximation holds when α < 5%.

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