Equal volumes of 0.1 M HCl and 0.1 M acetic acid (K_a=1.8x10^-5) are mixed. The pH of the mixture is nearest to (use log5=0.699)

JEE Main levelSingle correct optionDifficulty 2 of 3ie073

Equal volumes of $0.1 M$ $HCl$ and $0.1 M$ acetic acid ( $K_{a} = 1.8 \times 1 0^{- 5}$ ) are mixed. The pH of the mixture is nearest to (use $lo g 5 = 0.699$ )

After mixing,

[HCl] = 0.05 M

. The weak acid is further suppressed by the common

H X^{+}

(its contribution is of order

1 0^{- 5} M

, negligible). So

[H X^{+}] = 0.05 M

and

pH = 2 - 0.699 = 1.30