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Phosphate Buffer Equation:
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The phosphate buffer system is an important buffer in biological systems, particularly effective in the pH range of 6.8-7.4. It consists of monobasic phosphate (H₂PO₄⁻) and dibasic phosphate (HPO₄²⁻) ions in equilibrium.
The calculator uses the Henderson-Hasselbalch equation for phosphate buffer:
Where:
Explanation: The equation relates the pH of the buffer to the ratio of the concentrations of the basic and acidic forms of the phosphate buffer system.
Details: While phosphate buffer is most effective near its pKa (7.21), it can be used at pH 8.5 for specific applications. At this pH, the ratio of HPO₄²⁻ to H₂PO₄⁻ is approximately 19.5:1.
Tips: Enter concentrations of dibasic and monobasic phosphate in mol/L. Both values must be positive numbers. The calculator will determine the resulting pH of the buffer solution.
Q1: Why is phosphate buffer less effective at pH 8.5?
A: Phosphate buffer is most effective within ±1 pH unit of its pKa (7.21). At pH 8.5, it has reduced buffering capacity because one component (H₂PO₄⁻) is present in very low concentration.
Q2: What are typical applications of phosphate buffer at pH 8.5?
A: This pH is used in certain biochemical assays, enzyme studies, and electrophoresis procedures where alkaline conditions are required.
Q3: How do I prepare a phosphate buffer at pH 8.5?
A: Mix appropriate amounts of Na₂HPO₄ and NaH₂PO₄ solutions, using more of the dibasic form. Verify pH with a calibrated pH meter.
Q4: Does temperature affect the pH calculation?
A: Yes, the pKa of phosphate buffer changes with temperature. The calculator uses the pKa at 25°C (7.21).
Q5: What alternatives exist for buffering at pH 8.5?
A: Tris or carbonate buffers may be more effective at this pH, depending on the specific application requirements.