Buffer Density Calculator Formula

Henderson-Hasselbalch Equation:

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

pKa (acid dissociation constant):

[A-] (base concentration, M):

[HA] (acid concentration, M):

Calculated pH:

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1. What is the Henderson-Hasselbalch Equation?

The Henderson-Hasselbalch equation is used to estimate the pH of a buffer solution from the pKa of the acid and the concentrations of the acid and its conjugate base. It provides a simple way to calculate the pH of buffer systems in chemical and biological contexts.

2. How Does the Calculator Work?

The calculator uses the Henderson-Hasselbalch equation:

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

Where:

\( pKa \) — Acid dissociation constant
\( [A^-] \) — Concentration of conjugate base (M)
\( [HA] \) — Concentration of weak acid (M)

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

3. Importance of pH Calculation

Details: Accurate pH calculation is crucial for preparing buffer solutions in laboratory experiments, pharmaceutical formulations, and biological studies where maintaining specific pH ranges is essential.

4. Using the Calculator

Tips: Enter pKa value, base concentration in M, and acid concentration in M. All values must be valid (pKa ≥ 0, concentrations ≥ 0, acid concentration > 0).

5. Frequently Asked Questions (FAQ)

Q1: What is the valid range for this equation?
A: The equation works best when the ratio [A-]/[HA] is between 0.1 and 10, which corresponds to pH values within ±1 unit of the pKa.

Q2: When is the Henderson-Hasselbalch equation not accurate?
A: The equation may be less accurate for very dilute solutions, strong acids/bases, or when the concentrations approach the limits of the buffer capacity.

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 concentrations.

Q4: What are typical pKa values for common buffers?
A: Common buffers have pKa values around physiological pH (7.4), such as phosphate (pKa 7.2), Tris (pKa 8.1), and acetate (pKa 4.76).

Q5: How does temperature affect the calculation?
A: pKa values are temperature-dependent, so for precise calculations, use pKa values measured at the same temperature as your experiment.