Henderson-Hasselbalch Equation

What does the pKa tell us

Example Problem:

A solution is 0.04 M in HC₂H₃O₂ and 0.06 M in NaC₂H₃O₂. The K_a for acetic acid is 1.8 x 10^-5. Determine the pH of the solution.

Example Problem:

Determine the pH of a solution in which 1.00 mol of H₂CO₃ (K_a = 4.2x10^-7) and 0.500 mol NaHCO₃ are dissolved in enough water to form 1.00 L of solution.

Example Problem:

A buffer is prepared in which the ratio of HCO₃^- / CO₃^2- is 5.00. What is the pH of this buffer? Ka for HCO₃^- = 4.80 x 10^-11)

Example Problem:

Determine the amount (in grams) of sodium acetate (MW = 82.0 g/mol) to be added to 500.0 mL of 0.20 M acetic acid (Ka = 1.8 x 10-5) in order to make a buffer with pH = 5.00.

Biological Applications: Health Fields

Biological Buffer Systems: Acidosis and Alkalosis

Drug Ionization

Henderson-Hasselbalch Equation and Absorption of drugs

Example Problem:

1. 1. 1. Aspirin (a weak acid) has a pKa of 3.5. What is the percent ionized in the
      1. Lower stomach where the pH is 2.5 (food stays there for about 1-3 hours)
      2. Upper stomach (fundus) where the pH is 5.5 (food stays there for about 30-60 minutes)
    2. Diphenhydramine (a weak base) has a pKa of 9.1. At what pH will diphenhydramine be 90% ionized?