Dissociation constant of weak acid

  • #1
I'm preparing for a chemistry lab relating to "Determination of the dissociation constant of a eak acid".

In part of the lab, I will b doing the following for measuring "Ka" for ethanoic acid using the indicator method:

1- Mix ethanoic acid (0.02M, 5cm3) and sodium ethanoate (0.02M, 5cm3).
2- Add bromocresol green (10 drops) and mix thoroughly.

And, in the introduction to the lab, I'm given this information:
Hln(aq) <-----> H+(aq) + ln-(aq)
ka(Hln) = [H+][ln-] / [Hln]
ka(Hln) for bromocresol green = 2 x 10^-5 mol dm-3

Provided that, how can I answer those questions:
1- What is the ratio of [ln-]/[Hln] in the CH3COOH/CH3COONa mixture?
2- Using this equation "ka(Hln) = [H+][ln-] / [Hln]", calculate [H+] in the CH3COOH/CH3COONa mixture.
3- What is the value of Ka for ethanoic acid?

Thanks.
 

Answers and Replies

  • #2
Borek
Mentor
28,808
3,309
Explain complete procedure you are expected to follow, looks to me like there is something missing.
 

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