A solution is 0.25 M in HCl and 0.050 M in a weak acid HA (K_a = 3.0x10^-5). Assuming [H+] approx 0.25 M, find the degree of dissociation of HA in units of 10^-4 (two decimals).

JEE Main levelNumerical answerDifficulty 2 of 3ia193

A solution is $0.25 M$ in $HCl$ and $0.050 M$ in a weak acid $HA$ ( $K_{a} = 3.0 \times 1 0^{- 5}$ ). Assuming $[H X^{+}] \approx 0.25 M$ , find the degree of dissociation of $HA$ in units of $1 0^{- 4}$ (two decimals).

Numerical answer type, answer in x 10^-4, tolerance 0.01.

[A X^{-}] / [HA] = K_{a} / [H X^{+}]

, and since

α ≪ 1

α \approx K_{a} / [H X^{+}] = 3.0 \times 1 0^{- 5} /0.25 = 1.20 \times 1 0^{- 4} = 1.20 \times 1 0^{- 4}

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