Aqueous Equilibrium: Ka of an Unknown Acid via Titration

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SUMMARY

The discussion centers on determining the acid dissociation constant (Ka) of an unknown acid through titration with sodium hydroxide (NaOH). The titration involved an initial addition of 10.0 mL of NaOH, resulting in a pH of 5, followed by a total of 34.68 mL of NaOH before the addition of phenolphthalein, which indicated the endpoint by turning the solution deep pink. The subsequent addition of 2.62 mL of the unknown acid solution returned the solution to colorless, indicating the completion of the reaction. The key challenge identified is the lack of knowledge regarding the initial volume of the acid solution, which is critical for calculating the Ka.

PREREQUISITES
  • Understanding of acid-base titration techniques
  • Knowledge of pH measurement and interpretation
  • Familiarity with the concept of acid dissociation constant (Ka)
  • Experience with indicators, specifically phenolphthalein
NEXT STEPS
  • Research the calculation of Ka from titration data
  • Learn about the role of indicators in acid-base titrations
  • Study the principles of pH and its relationship to acid concentration
  • Explore methods for determining the concentration of unknown solutions
USEFUL FOR

Chemistry students, AP Chemistry tutors, and educators involved in teaching acid-base equilibria and titration techniques.

Svennerson
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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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