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Detemination of dissociation constants of weak acid

Procedure:
1. Pipette 25 cm3 of ethanoic acid into a conical flask
2. Titrate against 0.1M sodium hydroxide solution in the burrette, using phenolphthalein as indicator.
3. Pipette further 25 cm3 of ethanoic acid into the solution after titration and mix throughly.

Questions:
1. what is the retionship between pH and Ka
2. Is it important that the titre (volume of sodium hydroxide solution) should be exactly25cm3?
3. What is the purpose of adding a further portion of ethanoic acid to the solution after titration?
4. A student prepare 2 buffer solution
Buffer A : 0.5M ethanoic acid + 0.5M sodium ethanoate salt in equal volume
Buffer B : 5M ethanoic acid + 5M sodium ethanoate salt in equal volume
Do you think which is a good buffer? Why?
5. what discussion can be made on this experiment?
 

Answers and Replies

458
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So...what have you done so far? This isn't a place for you to receive full solutions from other members.
 
symbolipoint
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Use a pH meter instead of phenolphthalein and the topic title will make more sense.
 
chemisttree
Science Advisor
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It seems that you are being asked to discuss the relationship between pKa (-log[Ka]), pH, concentration of acid and concentration of it's conjugate base. Hmmmmm.
 

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