1. What is the Henderson-Hasselbalch Equation?

The Henderson-Hasselbalch equation is used to estimate the pH of a buffer solution. It relates the pH, pKa (the acid dissociation constant), and the ratio of the concentrations of the conjugate base [A⁻] and weak acid [HA] in the solution.

2. How Does the Calculator Work?

The calculator uses the Henderson-Hasselbalch equation:

Where:

• \( pH \) — The calculated pH of the buffer solution
• \( pKa \) — The acid dissociation constant of the weak acid
• \( [A^-] \) — Concentration of the conjugate base (mol/L)
• \( [HA] \) — Concentration of the weak acid (mol/L)

Explanation: The equation shows that the pH of a buffer solution depends on the pKa of the weak acid and the ratio of the concentrations of its conjugate base and the acid itself.

3. Importance of pH Calculation for Buffer Solutions

Details: Buffer solutions resist changes in pH when small amounts of acid or base are added. Accurate pH calculation is crucial in chemical, biological, and pharmaceutical applications where maintaining a stable pH is essential.

4. Using the Calculator

Tips: Enter the pKa value, and the concentrations of both [A⁻] and [HA] in mol/L. All concentration values must be greater than zero for accurate calculation.

5. Frequently Asked Questions (FAQ)

Q1: When is the Henderson-Hasselbalch equation most accurate?
A: The equation is most accurate when the concentrations of [A⁻] and [HA] are between 0.01M and 0.1M, and when the pKa is within ±1 unit of the desired pH.

Q2: What are the limitations of this equation?
A: The equation assumes ideal behavior and may not be accurate for very dilute solutions, very concentrated solutions, or when the acid is very strong or very weak.

Q3: Can this equation be used for polyprotic acids?
A: For polyprotic acids, the equation can be applied to each dissociation step separately, considering the appropriate pKa and concentration ratios.

Q4: Why is the ratio [A⁻]/[HA] important rather than absolute concentrations?
A: The pH depends on the ratio rather than absolute concentrations because the buffering capacity is determined by the equilibrium between the acid and its conjugate base.

Q5: How does temperature affect the calculation?
A: Temperature affects the pKa value of the acid. The equation should use the pKa value at the temperature of interest for accurate results.