1. What is the Henderson-Hasselbalch Equation?

The Henderson-Hasselbalch equation is used to estimate the pH of a solution containing a weak acid and its conjugate base. It provides a simplified way to calculate pH based on the acid dissociation constant (pKa) and the concentrations of the acid and salt forms.

2. How Does the Calculator Work?

The calculator uses the Henderson-Hasselbalch equation:

Where:

• \( pH \) — The calculated pH of the solution (dimensionless)
• \( pKa \) — The acid dissociation constant (dimensionless)
• \( [salt] \) — Concentration of the salt/conjugate base (mol/L)
• \( [acid] \) — Concentration of the weak acid (mol/L)

Explanation: The equation relates the pH of a buffer solution to the pKa of the weak acid and the ratio of concentrations of the conjugate base to the weak acid.

3. Importance of pH Calculation

Details: Accurate pH calculation is crucial for preparing buffer solutions in biochemical and chemical applications, maintaining stable pH conditions in biological systems, and understanding acid-base equilibria.

4. Using the Calculator

Tips: Enter pKa value, salt concentration in mol/L, and acid concentration in mol/L. All concentration values must be greater than zero.

5. Frequently Asked Questions (FAQ)

Q1: When is the Henderson-Hasselbalch equation valid?
A: The equation is most accurate when the concentrations of acid and salt are much greater than the concentration of H+ or OH- ions, typically within ±1 pH unit of the pKa.

Q2: What are typical pKa values for common acids?
A: Acetic acid: 4.76, Phosphoric acid (pKa1): 2.15, Carbonic acid (pKa1): 6.35. Different acids have different pKa values depending on their chemical structure.

Q3: Can this equation be used for basic buffers?
A: Yes, for basic buffers, the equation can be written as pOH = pKb + log([salt]/[base]).

Q4: What are the limitations of this equation?
A: The equation assumes ideal behavior, neglects activity coefficients, and becomes less accurate for very dilute solutions or when the pH is far from the pKa.

Q5: How is this equation used in practical applications?
A: It's widely used in biochemistry for preparing buffer solutions, in pharmaceutical formulations, and in analytical chemistry for predicting pH behavior.