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Henderson-Hasselbalch Equation:
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The Henderson-Hasselbalch equation is used to estimate the pH of buffer solutions. It relates the pH, pKa (acid dissociation constant), and the ratio of the concentrations of the conjugate base [A⁻] to the weak acid [HA] in the buffer system.
The calculator uses the Henderson-Hasselbalch equation:
Where:
Explanation: The equation demonstrates that the pH of a buffer solution depends on the pKa of the weak acid and the ratio of the concentrations of its conjugate base to the acid form.
Details: Accurate pH calculation is crucial for understanding buffer capacity, predicting chemical behavior in biological systems, and maintaining stable pH conditions in various chemical and biological processes.
Tips: Enter pKa value, concentration of conjugate base [A⁻] in mol/L, and concentration of weak acid [HA] in mol/L. All concentration values must be positive numbers.
Q1: What is the valid range for the Henderson-Hasselbalch equation?
A: The equation is most accurate when the ratio [A⁻]/[HA] is between 0.1 and 10, and when the concentrations are significantly higher than that of H⁺ and OH⁻ ions.
Q2: Can this equation be used for strong acids or bases?
A: No, the Henderson-Hasselbalch equation is specifically designed for weak acid-base buffer systems and is not applicable to strong acids or bases.
Q3: What are typical pKa values for common buffer systems?
A: Common biological buffers have pKa values around physiological pH (7.4), such as phosphate (pKa 7.2), Tris (pKa 8.1), and HEPES (pKa 7.5).
Q4: Are there limitations to this equation?
A: The equation assumes ideal behavior and may not account for ionic strength effects, temperature variations, or very dilute solutions where water dissociation becomes significant.
Q5: How does temperature affect the calculation?
A: Temperature affects both pKa values and the autoprotolysis constant of water, so for precise calculations, temperature-corrected pKa values should be used.