Henderson-Hasselbalch Equation Calculator

What is the Henderson-Hasselbalch Equation?

The Henderson-Hasselbalch equation is a fundamental principle in chemistry that relates the pH of a buffer solution to the pKa of the weak acid and the concentrations of the acid and its conjugate base. This equation is crucial in understanding and predicting the behavior of buffer solutions, which are essential in many biological and chemical processes.

Formula

The Henderson-Hasselbalch equation is expressed as:

\[ pH = pK_a + \log_{10}\left(\frac{[A^-]}{[HA]}\right) \]

Where:

• \(pH\) is the negative logarithm of the hydrogen ion concentration
• \(pK_a\) is the negative logarithm of the acid dissociation constant
• \([A^-]\) is the concentration of the conjugate base
• \([HA]\) is the concentration of the weak acid

Calculation Steps

Let's calculate the pH of a buffer solution with the following parameters:

• \(pK_a = 4.76\) (acetic acid)
• \([A^-] = 0.15\) M (concentration of acetate ion)
• \([HA] = 0.20\) M (concentration of acetic acid)

1. Input the values into the Henderson-Hasselbalch equation: \[ pH = 4.76 + \log_{10}\left(\frac{0.15}{0.20}\right) \]
2. Calculate the ratio inside the logarithm: \[ pH = 4.76 + \log_{10}(0.75) \]
3. Calculate the logarithm: \[ pH = 4.76 + (-0.1249) \]
4. Perform the final addition: \[ pH = 4.64 \]

Example and Visual Representation

Let's visualize the Henderson-Hasselbalch equation for our buffer solution:

This visual representation shows:

• The relative concentrations of the weak acid (HA) and its conjugate base (A⁻)
• The pKa of the weak acid (acetic acid)
• The resulting pH of the buffer solution (4.64)