1. Calculate the hydronium ion concentration, [H3O+] , for a solution with a pH of 7.48 . QUESTION #2 : What is the pH of a bleach solution that has a [OH−]=2.8×10−3 M?

Question

I am having trouble with these two questions can someone please furthermore explain them.

Answer 1

The definition of pH is the negative log of the [H₃O⁺]. So if you know the pH, you can find the [H₃O⁺] and if you know the [H₃O⁺] you can find the pH. In question 1, you are given the pH of 7.48 and asked to find the [H₃O⁺]. pH = -log [H₃O⁺]

[H₃O⁺] = 1x10^-pH = 1x10^-7.48 = 3.3x10^-8 M (these conversions are algebra/math so you may need to review)

In question 2, you are given the [OH-] and asked to find the pH. The relationship between [H₃O⁺] and [OH-] is

H₃O⁺ x OH- = 1x10^-14

H₃O⁺ = 1x10^-14 / [OH-] = 1x10^-14 / 2.8x10^-3 = 3.57x10^-12 M

pH = -log [H₃O⁺] = -log 3.57x10^-12

pH = 11.4

Done another way:

pH + pOH = 14

pOH = -log [OH-] = -log 2.8x10-3

pOH = 2.55

pH = 14 - pOH = 14 - 2.55

pH = 11.4