Ph Buffer Calculator

Henderson-Hasselbalch Equation:

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

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 chemistry and biology.

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 understanding buffer capacity, preparing buffer solutions in laboratory settings, and predicting how buffer systems will respond to added acid or base.

4. Using the Calculator

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

5. Frequently Asked Questions (FAQ)

Q1: What is the valid range for the Henderson-Hasselbalch equation?
A: The equation works best when the concentration 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 acid concentration is extremely low relative to the base.

Q3: What are typical pKa values for common buffers?
A: Common buffer pKa values include: acetic acid (4.76), phosphate (7.2), Tris (8.06), and carbonate (10.3).

Q4: 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.

Q5: How does temperature affect the calculation?
A: Temperature affects both pKa values and the actual pH of the solution. The equation uses the pKa at the specific temperature of interest.