A weak monobasic acid (K_a = 2.0x10^-5) is 2% ionised in solution. Using K_a = (calpha^2)/(1-alpha), find its molar concentration to three decimals.

JEE Main levelNumerical answerDifficulty 2 of 3ie027

A weak monobasic acid ( $K_{a} = 2.0 \times 1 0^{- 5}$ ) is $2%$ ionised in solution. Using $K_{a} = \frac{c α ^{2}}{1 - α}$ , find its molar concentration to three decimals.

Numerical answer type, answer in M, tolerance 0.001.

c = K_{a} (1 - α) / α^{2} = 2.0 \times 1 0^{- 5} \times 0.98/ (0.02)^{2} = 0.0490 \approx 0.049 M