1. What impact does solution volume have on pH? 2. What has a higher pH [H3O+], 0.1 M HCl or 0.01 M HCl?

Answer 1

If only the volume of the solution changes, this is a dilution. If there is an acid or a base in the solution, the concentration of that will decrease as the volume of solution increases, so the pH will get closer to neutrality (pH 7). So, if you have an acidic solution, dilution will raise the pH. If you have a basic (alkaline) solution, dilution will lower the pH.

Are you asking which solution has a higher pH or a higher [H₃O⁺]? They are opposite, so the one with a higher pH has a lower [H₃O⁺]. In this problem, 0.1 M HCl will have a higher [H₃O⁺] and a lower pH than 0.01 M HCl. Conversely, 0.01 M HCl will have a lower [H₃O⁺] and a higher pH than 0.1 M HCl.