Aqueous Equilibrium: Ka of an Unknown Acid via Titration

AI Thread Summary
The discussion revolves around determining the Ka of an unknown acid using titration data, where an initial pH of 5 was recorded after adding 10.0 mL of NaOH. After 34.68 mL of NaOH, the addition of phenolphthalein indicated a significant pH change, turning the solution deep pink. Further addition of 2.62 mL of the unknown acid made the solution colorless again, suggesting the endpoint was reached. Participants express confusion over how to calculate Ka without knowing the initial volume of the acid solution. The consensus highlights the necessity of additional information to solve the problem effectively.
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Homework Statement


We're given an unknown acid, and dissolve an unknown mass of the acid in an unknown amount of water. We then titrated the solution with an unknown molarity solution of NaOH. After titrating in 10.0 mL of NaOH, we measure a pH of 5. After 34.68 mL of NaOH, we realize we forgot to add phenolphthaelin. Adding it in turns the solution deep pink. Adding in another 2.62 mL of the unknown acid solution turns the solution colorless again. Find the Ka of the acid.

We are absolutely stumped on this one, please help.
 
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I can be missing something, but I don't see how to solve without knowing the initial volume of the acid solution.
 
I'm an AP Chem tutor, and this stumps me for the same reason.
 
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