pH and Buffers: Acid-Base Reactions and Henderson-Hasselbalch Equation

Brønsted-Lowry Definition of a Base

• A Brønsted-Lowry base is a substance that accepts a proton (H+)

Henderson-Hasselbalch Equation

• Calculates the pH of a buffer solution
• Equation: pH = pKa + log ([conjugate base]/[acid])

Buffer Effectiveness

• Buffers are most effective when the pH is close to the pKa of the acid
• The buffer is able to resist changes in pH when there is a roughly equal concentration of the acid and its conjugate base

pKa of an Acid

• Indicates the acid's strength in a solution
• Lower pKa: Stronger acid
• Higher pKa: Weaker acid

pKa Significance in the Henderson-Hasselbalch Equation

• The pKa value in the Henderson-Hasselbalch equation represents the pH at which the concentrations of the acid and its conjugate base are equal

Inorganic Phosphate pKa Values

• Inorganic phosphate (H3PO4) has multiple pKa values because it can donate multiple protons in a stepwise fashion.
• Important for buffering within biological systems since it can act as a buffer over a broad pH range

Conjugate Acid-Base Pair and pH

• The Henderson-Hasselbalch equation demonstrates the relationship between the pH and the relative amounts of a conjugate acid-base pair
• When the pH is equal to the pKa, the concentrations of the acid and its conjugate base are equal
• As the pH increases, the concentration of the conjugate base increases relative to the concentration of the acid
• As the pH decreases, the concentration of the acid increases relative to the concentration of the conjugate base

Test your understanding of acid-base reactions, the Brønsted-Lowry definition, strong and weak acids, and the Henderson-Hasselbalch equation in the context of pH and buffers. This quiz covers material from Lecture 2 of BCMB 401, Spring 24, focusing on Chapter 1.3 of the reading.