• Support PF! Buy your school textbooks, materials and every day products Here!

PH/Titration Question

  • Thread starter woox
  • Start date
  • #1
17
0

Homework Statement


Calculate the pH at the equivalence point for the titration of 0.20 M NH3 with 0.20 M HCl? Kb of ammonia is 1.8e-5

This is just a old test I am going over, I managed to get a pH of 4.98. but that is not right the right answer is 5.12 and I cant figure out why. I would assume you could use the henderson equation but I only get 4.98 which is wrong.

Any help?
 

Answers and Replies

  • #2
Borek
Mentor
28,326
2,710
  • #3
17
0
  • #4
Borek
Mentor
28,326
2,710
So show details of your work, hard to say what you did wrong not knowing what you did.
 
  • #5
17
0
So show details of your work, hard to say what you did wrong not knowing what you did.
k.... using ICE table below:

2145854.jpg
 
  • #6
Borek
Mentor
28,326
2,710
Please reread my very first post in this thread. Every word of it.
 
  • #7
17
0
Please reread my very first post in this thread. Every word of it.
I did and didn not use the HH eq, not do i understand what you mean by dilution.

I also read link, and this is onlything really useful that I understood but still does not explain what I am doing wrong:
In the case of titration of weak base with strong acid, situation is very similar - pH at the equivalence point is determined by the weak base salt hydrolysis. Thus we need pKa of conjugated acid to calculate H+ and pH. Check lecture and cheat sheet mentioned above for details.

It would be great if you told me what I am doing wrong...
 
  • #8
Borek
Mentor
28,326
2,710
Try here: dilution effects. Generally speaking, you have mixed two solutions, concentrations have changed as the final volume differs from the initial for each reagent.
 

Related Threads for: PH/Titration Question

  • Last Post
2
Replies
26
Views
3K
  • Last Post
Replies
3
Views
949
  • Last Post
Replies
1
Views
5K
  • Last Post
Replies
12
Views
763
  • Last Post
Replies
10
Views
5K
  • Last Post
Replies
1
Views
3K
  • Last Post
Replies
1
Views
2K
Replies
1
Views
2K
Top