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Henderson-Hasselbalch Calculator

Formula

To calculate the pH using the Henderson-Hasselbalch equation:

$pH = K_a + \log \left( \frac{[A^-]}{[HA]} \right)$

Where:

$pH$ is the measure of the acidity of the solution
$K_a$ is the acid dissociation constant
$[A^-]$ is the molar concentration of the base
$[HA]$ is the molar concentration of the acid

Henderson-Hasselbalch Equation Definition

The Henderson-Hasselbalch equation is a formula used to calculate the pH (acidity) of a buffer. The equation is denoted:

$pH = K_a + \log \left( \frac{[A^-]}{[HA]} \right)$

A buffer is a mixture or solution that contains a weak acid and a conjugate base. The combination of these two components, while at equilibrium, helps to maintain a stable pH in the solution.

Example Calculation 1

Let's assume the following values:

Acid Dissociation Constant ( $K_a$ ) = 4.75
Molar Concentration of Base ( $[A^-]$ ) = 0.1 M
Molar Concentration of Acid ( $[HA]$ ) = 0.2 M

Using the formula:

$pH = 4.75 + \log \left( \frac{0.1}{0.2} \right) = 4.75 + \log (0.5) \approx 4.75 + (-0.3010) = 4.06$

The pH of the solution is approximately 4.06.

Example Calculation 2

Let's assume the following values:

Acid Dissociation Constant ( $K_a$ ) = 3.75
Molar Concentration of Base ( $[A^-]$ ) = 0.05 M
Molar Concentration of Acid ( $[HA]$ ) = 0.05 M

Using the formula:

$pH = 3.75 + \log \left( \frac{0.05}{0.05} \right) = 3.75 + \log (1) = 3.75 + 0 = 3.75$

The pH of the solution is approximately 3.75.