How many litres of water must be added to a litre of an aqueous solution of HCl with a pH of 1 to create an aqueous solution with a pH of 2?

Initial pH = 1, i.e., [H+] = 0.1 mole/litre
New pH = 2, i.e., [H+] = 0.01 mole/litre
V1 = 1 litre
Let V2 be the volume of the new solution.
Using the dilution formula:
[H+]1V1 = [H+]2V2
0.1 × 1 = 0.01 × V2
V2 = 10 litres
Therefore, the volume of water added = V2 - V1 = 10 - 1 = 9 litres