PH/Titration Question

  • Thread starter woox
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  • #1
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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

  • #4
Borek
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So show details of your work, hard to say what you did wrong not knowing what you did.
 
  • #5
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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
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Please reread my very first post in this thread. Every word of it.
 
  • #7
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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
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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.
 

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