Detemination of dissociation constants of weak acid

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SUMMARY

The forum discussion centers on the determination of dissociation constants (Ka) of weak acids, specifically using ethanoic acid and sodium hydroxide. The procedure involves titration with a 0.1M sodium hydroxide solution and the use of phenolphthalein as an indicator. Key questions include the relationship between pH and Ka, the significance of the titration volume, and the purpose of adding additional ethanoic acid post-titration. The discussion also evaluates two buffer solutions, highlighting the importance of buffer capacity in relation to their concentrations.

PREREQUISITES
  • Understanding of weak acid dissociation and the concept of Ka
  • Familiarity with titration techniques and the use of indicators like phenolphthalein
  • Knowledge of buffer solutions and their preparation
  • Basic principles of pH measurement and its relationship to acidity
NEXT STEPS
  • Research the relationship between pH and dissociation constants (Ka) in weak acids
  • Learn about the preparation and characteristics of buffer solutions
  • Explore the use of pH meters for accurate pH measurement in titrations
  • Investigate the impact of concentration on buffer capacity and effectiveness
USEFUL FOR

Chemistry students, laboratory technicians, and educators involved in acid-base titration experiments and buffer solution preparation.

chiakimaron
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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?
 
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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.
 
Use a pH meter instead of phenolphthalein and the topic title will make more sense.
 
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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