[rosco_pk]

Hello folks, wondering if you can help with a question that is challenging myself and a couple of classmates.
The question is not homework and wont be needed for our final exam but it is set out in the notes as a Challenge Question and the three of us are having some trouble answering it. We have the answers from the notes and have tried working backwards but to no avail.

Q: Calculate the pH of the solution formed when:
   
    a) 35 cm³M NaOH are added to 50 cm³M ethanoic acid. (K_a = 1.8 x 10^-5)
   
    b) 20 cm³M HCL are added to 50 cm³M NH₄OH (K_b = 1.8 x 10^-5)

Any help would be appreciated and if possible an explanation of how you worked through it. The answers in the notes say a) = 5.11 and b) = 9.1 but having worked through a lot of the questions in the notes quite a few answers are wrong so that could very well be the case here.

Thanks

Rosco
   
P.S. - this is all the information that is given for the question.

[Borek]

http://www.chembuddy.com/?left=pH-calculation&right=pH-buffers-henderson-hasselbalch

[AWK]

cm³M

What does mean?
Define concentrations of your solutions!

[rosco_pk]

Im presuming it means Mols per cm³ but thats exactly as it is written in the question. I cant define it. Thats all the information we are given in the question.

[Borek]

cm³M

What does mean?
Define concentrations of your solutions!

Wow, missed this one. No concentrations, no answers.

[AWK]

Im presuming it means Mols per cm³ but thats exactly as it is written in the question. I cant define it. Thats all the information we are given in the question.

For calculations you should use a molar concentratiom  1M = 1 mol/dm³

[rosco_pk]

Hi thanks for the advice. Our tutor has decided to remove the question from the notes. He deems it unnecessary for the course. Blinking SQA are crap!