A 11.1 mL sample of a HCl solution has a pH of 2.000. What volume of water must be added to change the pH to 4

Question

A 11.1 mL sample of a HCl solution has a pH of 2.000. What volume of water must be added to change the pH to 4.000?
mL

Answer 1

the molarity of H+ in the solution : 10^-2 = 0.01M
the moles of H+ in the first solution : 0.01 * 11.1*10^-3 = 1.11*10^-4
the moles of H+ in the second solution : 10^-4 M
the volume of the second solution : 1.11*10^-4 / 10^-4 = 1.11L
the volume of water needed : 1.11 - 11.1*10^-3 = 1.0989 L