HX has K_a = 4x10^-5 and HY has K_a = 1x10^-6 (both weak, alpha ll 1). If 0.1 M HX has the same degree of ionisation as HY solution of molarity c, then c is

JEE Advanced levelSingle correct optionDifficulty 3 of 3ie049

HX has $K_{a} = 4 \times 1 0^{- 5}$ and HY has $K_{a} = 1 \times 1 0^{- 6}$ (both weak, $α ≪ 1$ ). If $0.1 M$ HX has the same degree of ionisation as HY solution of molarity $c$ , then $c$ is

α = K_{a} / c

. Equal

α

requires

K_{X} / c_{X} = K_{Y} / c_{Y}

, so

c_{Y} = c_{X} K_{Y} / K_{X} = 0.1 \times 1 0^{- 6} / (4 \times 1 0^{- 5}) = 0.0025 M