Citrate Buffer Calculator

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 buffer pH and is widely used in chemistry and biochemistry.

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 base to acid concentrations in a buffer system.

3. Importance of pH Calculation

Details: Accurate pH calculation is crucial for preparing buffer solutions in laboratory experiments, pharmaceutical formulations, and biological research where maintaining specific pH levels 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).

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 assumes ideal behavior and may not be accurate for very concentrated solutions, when ionic strength is high, or for very weak/strong acids.

Q3: What are typical pKa values for citrate buffer?
A: Citric acid has three pKa values: pKa1 = 3.13, pKa2 = 4.76, pKa3 = 6.40, depending on which proton is being considered.

Q4: Can this be used for polyprotic acids?
A: For polyprotic acids like citrate, the equation can be applied to each dissociation step separately when the pKa values are sufficiently separated.

Q5: Why is buffer capacity important?
A: Buffer capacity determines how well a solution resists pH changes when acid or base is added. Maximum buffer capacity occurs when pH = pKa.