Phosphate Buffer Calculator Ph

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 a chemical formula used to estimate the pH of a buffer solution. For phosphate buffers, it relates the pH to the pKa of the phosphate system and the ratio of conjugate base to acid concentrations.

2. How Does the Calculator Work?

The calculator uses the Henderson-Hasselbalch equation:

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

Where:

\( pH \) — Resulting pH of the buffer solution (dimensionless)
\( pKa \) — Acid dissociation constant (dimensionless)
\( [A^-] \) — Concentration of conjugate base
\( [HA] \) — Concentration of weak acid
\( \frac{[A^-]}{[HA]} \) — Ratio of base to acid (dimensionless)

Explanation: The equation shows that pH depends on both the pKa value of the acid and the ratio of the concentrations of the conjugate base and acid forms.

3. Importance of pH Calculation in Phosphate Buffers

Details: Accurate pH calculation is crucial for preparing phosphate buffers in biological and chemical applications, as many biochemical processes are highly sensitive to pH changes.

4. Using the Calculator

Tips: Enter the pKa value for the phosphate system (typically 7.2 for the H₂PO₄⁻/HPO₄²⁻ system) and the ratio of [A⁻]/[HA]. Both values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is the typical pKa value for phosphate buffers?
A: The primary phosphate buffer system (H₂PO₄⁻/HPO₄²⁻) has a pKa of approximately 7.2 at 25°C.

Q2: Why is the ratio dimensionless?
A: The ratio [A⁻]/[HA] is dimensionless because it represents a ratio of concentrations with the same units that cancel out.

Q3: What is the effective buffer range for phosphate buffers?
A: Phosphate buffers are most effective in the pH range of approximately 6.2-8.2 (pKa ± 1).

Q4: Does temperature affect the pKa value?
A: Yes, pKa values are temperature-dependent. The pKa of phosphate decreases by about 0.0028 units per degree Celsius increase.

Q5: Can this calculator be used for other buffer systems?
A: Yes, the Henderson-Hasselbalch equation applies to any acid-base buffer system when you use the appropriate pKa value.