To what volume one litre of 0.6 molar acetic acid must be diluted in order to double its pH?Ka=1.8×10^-5

Answer 1

You want to DOUBLE the pH? Not sure about that, but I'll go through the process despite my questioning the legitimacy of the exercise.

Acetic acid is CH3COOH. In water you have CH3COOH <==> CH3COO^- + H⁺

Ka = 1.8x10^-5 = [H⁺][CH3COO^-]/[CH3COOH]

1.8x10^-5 = (x)(x)/0.6

x² = 1.08x10^-5

x = [H⁺] = 3.29x10^-3 M

pH = -log [H⁺] = 2.48

So, now you want to dilute this so that the pH = 2 x 2.48 = 4.96?

To do this, you now want the [H⁺] to become 1x10^-4.96 = 1.1x10^-5 M

(1 L)(0.6 M) = (x L)(1.1x10^-5 M)

x = 5.5x10⁴ liters

So, you would have to dilute the original 1 liter of 0.6 M acetic acid to a volume of 5.5x10⁴ liters (55000 liters)