I have 10 mL of water with a ph of 12.82, how much water with a ph of 9.43 will I need to add to reduce the ph to 11.5

Answer 1

You have on hand:

pH = 12.82. What is the [H⁺]?

[H⁺] = 1x10^-12.82 = 1.5x10^-13 M

pH = 9.43. What is the [H⁺]?

[H⁺] = 1x10^-9.43 = 3.7x10^-10 M

You want to produce:

pH = 11.5. What is the [H⁺]?

[H⁺] = 1x10^-11.5 = 3.2x10^-12 M

(x ml)(3.7x10^-10) + (10 ml)(1.5x10^-13) = (x + 10 ml)(3.2x10^-12)

Solving for x, you get

x = 0.08 mls of pH 9.43 water should be added.

(be sure to check my math)