Textbook 6B.9 question

[Norah Gidanian 3D]

I wasnt sure where to put this question because there is no forum for acid and base equilibrium but one of the textbook questions asks for the ph and gives us the [H3O+]=1.5mol/L so I took the negative log of 1.5 and got -.176 but the answer key says it is .176. Can anyone explain why

[Mursall M 2A]

Hi! I also got the same answer! I believe that someone mentioned it could be a typo!

[Faaizah Arshad 1H]

The answer key has a mistake; it should include a negative sign. It makes sense for the answer for this to be negative because when the [H30+] > 1 M, then the pH will be below 0. You are correct!

[Sam_Marasigan_3D]

Yes, you're correct! Dr. Lavelle mentioned in his discussion section that it was a typo :)

[Sophia Hu 1A]

To add on to what everyone else said, I think for (i) the [OH-] should be 6.67 x 10^-15 M because [OH-] = Kw/[H3O+] = (1.0 x 10^-14)/1.5 = 6.67 x 10^-15. pOH = - log(6.67 x 10^-15) = 14.176. This also makes sense because pOH = 14 - pH = 14 - (-0.176) = 14.176.

Then for (ii) Given that [OH-] = 1.50 M, the pOH = -0.176. Using a similar method as stated above, you can find that [H3O+] = 6.67 x 10^-15 M and pH = 14.176. This makes sense because in this case, there is more than 1.0 M OH-, so the pH must be greater than 14.

I believe those were the only two parts of the problem with an error. I hope this helps!