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 (acid dissociation constant), and the ratio of the concentration of the conjugate base [A⁻] to the concentration of the weak acid [HA].

2. How Does the Calculator Work?

The calculator uses the Henderson-Hasselbalch equation:

Where:

• \( pH \) — pH of the buffer solution (dimensionless)
• \( pKa \) — Acid dissociation constant (dimensionless)
• \( [A^-] \) — Concentration of conjugate base (mol/L)
• \( [HA] \) — Concentration of 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 Buffer pH Calculation

Details: Buffer solutions resist changes in pH when small amounts of acid or base are added. Calculating buffer pH is essential in biochemistry, pharmaceuticals, and analytical chemistry where maintaining a stable pH is critical.

4. Using the Calculator

Tips: Enter pKa value, concentrations of conjugate base [A⁻] and weak acid [HA] in mol/L. All concentration values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: When is the Henderson-Hasselbalch equation valid?
A: The equation is most accurate when the concentrations of [A⁻] and [HA] are much greater than the concentration of H⁺ or OH⁻ ions, typically when [A⁻]/[HA] ratio is between 0.1 and 10.

Q2: What are common buffer systems?
A: Common buffer systems include acetate (acetic acid/sodium acetate), phosphate (monobasic/dibasic phosphate), and carbonate (carbonic acid/bicarbonate).

Q3: How does temperature affect pKa values?
A: pKa values are temperature-dependent. Most acids have pKa values that decrease slightly with increasing temperature.

Q4: What is buffer capacity?
A: Buffer capacity refers to the amount of acid or base that can be added to a buffer before its pH changes significantly. Maximum buffer capacity occurs when pH = pKa.

Q5: Are there limitations to this equation?
A: The equation assumes ideal behavior and may not be accurate for very concentrated solutions, polyprotic acids, or when ionic strength effects are significant.