1. What is the Phosphate Buffer Equation?

The phosphate buffer equation is derived from the Henderson-Hasselbalch equation and calculates the ratio of monobasic to dibasic phosphate needed to achieve a specific pH. Phosphate buffers are commonly used in biological and chemical applications.

2. How Does the Calculator Work?

The calculator uses the following equation:

Where:

• \( [H_2PO_4^-] \) — Concentration of monobasic phosphate
• \( [HPO_4^{2-}] \) — Concentration of dibasic phosphate
• \( pKa \) — Acid dissociation constant (typically 7.2 for phosphate buffer at 25°C)
• \( pH \) — Desired pH of the buffer solution

Explanation: The equation shows the ratio of acid to conjugate base needed to achieve a specific pH in a buffer system.

3. Importance of Phosphate Buffer

Details: Phosphate buffers are essential in biological systems and laboratory experiments because they maintain stable pH conditions, which is crucial for enzyme activity and chemical reactions.

4. Using the Calculator

Tips: Enter the pKa value (typically 7.2 for phosphate buffer at 25°C) and your desired pH. The calculator will output the required molar ratio of monobasic to dibasic phosphate.

5. Frequently Asked Questions (FAQ)

Q1: What is the typical pKa for phosphate buffer?
A: The second pKa of phosphoric acid is typically 7.2 at 25°C, which is most relevant for biological pH ranges.

Q2: What is the effective range of phosphate buffer?
A: Phosphate buffers are most effective in the pH range of 6.2 to 8.2 (pKa ± 1).

Q3: How do I prepare the actual buffer solution?
A: Mix appropriate amounts of NaH2PO4 (monobasic) and Na2HPO4 (dibasic) according to the calculated ratio, then dilute to desired volume.

Q4: Does temperature affect the pKa?
A: Yes, the pKa of phosphate buffer changes slightly with temperature (about -0.0028 units per °C).

Q5: Can I use this for other buffer systems?
A: The same equation applies to other buffers, but you must use the appropriate pKa for that specific buffer system.