Question

Hi,

The problem is:
"Calculate the concentration of OH- and the pH value of an aqueous solution in which [H30+] is 0.014M at 25C. Is this solution acidic, basic, or neutral?"

I have calculated the OH- concentration to be: 7.1 X 10^-14

When I calculate the pH (using H30+), I get a pH of .85. Is that possible? If I calculate using OH-, I get a pH of 13.15. With such widely different answers, I want to be sure I am doing this right.

This is an online class, so no lecture to rely on for help! Thanks!

Answer 1

You're right to be confused. I get 1.85 for pH (which makes it an acid solution).
pH = -log(H^+) = -log(0.014) = -(-1.85) = 1.85. Then for OH^-, I do it this way.
pH + pOH = pKw = 14
1.85 + pOH = 14 which makes pOH = 14 - 1.85 = 12.15
Then solve pOH = -log(OH^-)
12.15 = -log(OH^-)
(OH^-) = 7.14 x 10^-13

Answer 2

Thank you!