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pH = pKa for equal [HA] and [A⁻],Yes, in buffer.,pH (dimensionless), pKa (dimensionless)
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The Henderson-Hasselbalch equation is a chemical equation used to calculate the pH of buffer solutions. It relates the pH, pKa (acid dissociation constant), and the ratio of concentrations of the conjugate base [A⁻] to the weak acid [HA] in the solution.
The calculator uses the Henderson-Hasselbalch equation:
Where:
Special Case: When [A⁻] = [HA], the equation simplifies to pH = pKa, which is the point of maximum buffering capacity.
Details: This calculation is essential for preparing buffer solutions in chemistry and biochemistry laboratories, understanding acid-base equilibria, and predicting how pH changes with varying concentrations of acid and conjugate base.
Tips: Enter the pKa value, concentrations of conjugate base and acid in molar units (M). All concentrations must be positive values, and the acid concentration cannot be zero.
Q1: When is pH equal to pKa?
A: pH equals pKa when the concentrations of the conjugate base [A⁻] and weak acid [HA] are equal.
Q2: What is the valid range for this equation?
A: The equation works best when the concentrations of [A⁻] and [HA] are within 0.1 to 10 times each other, and when the pKa is within ±1 unit of the desired pH.
Q3: Can this equation be used for strong acids?
A: No, the Henderson-Hasselbalch equation is only valid for weak acids and their conjugate bases.
Q4: What are the limitations of this equation?
A: The equation assumes ideal behavior and may not be accurate at very high concentrations or when ionic strength effects are significant.
Q5: How accurate is pH calculation from pKa?
A: For most practical purposes in buffer preparation, the calculation provides sufficient accuracy, though experimental verification is recommended for critical applications.