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Henderson-Hasselbalch Equation:
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The Henderson-Hasselbalch equation is used to estimate the pH of a buffer solution. It relates the pH, pKa (acid dissociation constant), and the ratio of the concentrations of the conjugate base [A⁻] and weak acid [HA] in the solution.
The calculator uses the Henderson-Hasselbalch equation:
Where:
Explanation: The equation shows 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.
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 greater than zero.
Q1: What is a buffer solution?
A: A buffer solution is one that resists changes in pH when small amounts of acid or base are added, typically composed of a weak acid and its conjugate base.
Q2: When is the Henderson-Hasselbalch equation valid?
A: The equation is most accurate when the concentrations of [A⁻] and [HA] are much larger than the concentration of H⁺ or OH⁻ ions, typically within ±1 pH unit of the pKa.
Q3: What are typical pKa values?
A: pKa values vary widely depending on the acid. For example, acetic acid has pKa ≈ 4.76, while phosphoric acid has multiple pKa values (2.14, 7.20, 12.67).
Q4: Can this equation be used for strong acids?
A: No, the Henderson-Hasselbalch equation is specifically designed for weak acid buffers and is not applicable to strong acids or bases.
Q5: What are the limitations of this equation?
A: The equation assumes ideal behavior, neglects activity coefficients, and becomes less accurate when the ratio [A⁻]/[HA] is very large or very small, or when dealing with very dilute solutions.