6B. 1

[Kaitlin Joya 1I]

The molar concentration of HCl in hydrochloric acid is reduced to 12% of its initial value by dilution. What is the difference in the pH values of the two solutions?

What is the exact math behind this? I know for a 1 pH difference, the hydronium concentration changes 10x but I don't know how to apply it to this or if that's what I need to use.

[Aditya Desai 1A]

If you set the conc. of the original solution to 1 M (pH = 0). Dilute to .12: -log(.12) = .921 = answer.

[Justin_Choo_3J]

Hello!!

To provide thorough mathematical contest, the change in pH can be calculated using this equation: (delta)pH = -log((0.12 x [HCl])/[HCl]). The bracketed "[HCl]" represents the molar concentration of HCl which you can obtain by the periodic table (36.461) and "0.12" accounts for the 88% reduction of said molar concentration. You can simply cancel out [HCl] and you would be left with (delta)pH = -log(0.12) which equates to 0.92, which is your change in pH.

[Kaitlin Joya 1I]

Why is the pH of the original solution 0?

[Rainy Liu Ruoshui_2K]

Why is the pH of the original solution 0?

This is a simple assumption. In this case, she assumed the original concentration of hydrogen ions to be 1M.

[Kaitlin Joya 1I]

Is that the case for all acids then, even weak ones? If they are 1 M, you assume their pH to be 0?