Calculating Acetic Acid Concentration: Henderson Hasselback

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SUMMARY

The discussion centers on calculating the concentration of acetic acid in a 250mL solution of a 100mM acetate buffer at pH 4.76 using the Henderson-Hasselbalch equation. The user initially calculated the concentration of acetic acid as 25mM by incorrectly using a value of 0.025 for the concentration of acetate ion ([A-]). The correct concentration of acetic acid should be 50mM, as the pH equals the pKa, indicating that [A-] equals [HA]. This highlights the importance of understanding the relationship between pH, pKa, and the concentrations of acid and conjugate base in buffer solutions.

PREREQUISITES
  • Understanding of the Henderson-Hasselbalch equation
  • Knowledge of pH and pKa concepts
  • Familiarity with buffer solutions and their components
  • Basic skills in molarity calculations
NEXT STEPS
  • Study the Henderson-Hasselbalch equation in detail
  • Learn about buffer capacity and its implications in biochemical systems
  • Explore the relationship between pH, pKa, and concentrations of acids and bases
  • Practice calculating concentrations in various buffer solutions
USEFUL FOR

Chemistry students, laboratory technicians, and anyone involved in biochemical research or applications requiring buffer solution calculations.

EKG
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Homework Statement


What is the concentration of acetic acid in 250mL of a 100mM acetate buffer at pH 4.76?


Homework Equations


Henderson Hasselback


The Attempt at a Solution


I used the Henderson Hasselback equation. plugged in 4.76 for pKa. plugged in .025 for the concentration of A-. plugged in 4.76 for pH. Solved and got 25mM. The answer is supposed to be 50mM. Would appreciate the help, thanks.
 
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EKG said:

Homework Statement


What is the concentration of acetic acid in 250mL of a 100mM acetate buffer at pH 4.76?


Homework Equations


Henderson Hasselback


The Attempt at a Solution


I used the Henderson Hasselback equation. plugged in 4.76 for pKa. plugged in .025 for the concentration of A-. plugged in 4.76 for pH. Solved and got 25mM. The answer is supposed to be 50mM. Would appreciate the help, thanks.

You don't give any reason for having plugged in 0.25 for the molarity of A-.

Anyway time to fix in mind the often useful fact that when pH = pK then [A-] = [HA] and get clear why. Since here pH does = pK, when you plug in any value for [A-] you will get the same value for [HA], as you did.
 

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