1. What is the Phosphate Buffer Equation?

The phosphate buffer equation calculates the concentration of dibasic phosphate (HPO4^2-) in a buffer solution based on total phosphate concentration, pH, and pKa2. It's essential for preparing biological and chemical buffers.

2. How Does the Calculator Work?

The calculator uses the phosphate buffer equation:

Where:

• \( total \) — Total phosphate concentration (mol/L)
• \( pH \) — Desired pH of the buffer solution
• \( pKa2 \) — Second dissociation constant of phosphoric acid (≈7.21)

Explanation: The equation calculates the fraction of total phosphate that exists in the dibasic form (HPO4^2-) at a given pH.

3. Importance of Phosphate Buffer Calculation

Details: Accurate phosphate buffer preparation is crucial for maintaining stable pH in biological experiments, medical applications, and chemical processes.

4. Using the Calculator

Tips: Enter total phosphate concentration in mol/L, desired pH (typically between 6.0-8.0 for biological buffers), and pKa2 (default is 7.21). All values must be valid (total > 0, pH between 0-14).

5. Frequently Asked Questions (FAQ)

Q1: What is the typical pKa2 value for phosphate buffer?
A: The second dissociation constant (pKa2) of phosphoric acid is approximately 7.21 at 25°C.

Q2: What pH range is phosphate buffer effective for?
A: Phosphate buffers are most effective in the pH range of 6.0-8.0, centered around the pKa2 of 7.21.

Q3: How do I prepare the actual buffer solution?
A: Combine appropriate amounts of monobasic (H2PO4^-) and dibasic (HPO4^2-) phosphate salts based on the calculated ratio.

Q4: Does temperature affect the calculation?
A: Yes, pKa values are temperature-dependent. The default pKa2 of 7.21 is for 25°C.

Q5: What ionic strength should I use?
A: For precise work, adjust ionic strength to match your experimental conditions as it affects pKa values.