To 1 L of buffer containing 0.20 M CH3COOH and 0.20 M CH3COONa (pK_a = 4.74), 0.02 mol HCl gas is added without volume change. The new pH is

JEE Main levelSingle correct optionDifficulty 2 of 3ie128

To 1 L of buffer containing 0.20 M $CH X_{3} COOH$ and 0.20 M $CH X_{3} COONa$ ( $p K_{a} = 4.74$ ), 0.02 mol HCl gas is added without volume change. The new pH is

HCl converts acetate to acid: acetate = 0.18 mol, acid = 0.22 mol. pH =

4.74 + lo g (0.18/0.22) = 4.74 - 0.087 = 4.65