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Henderson-Hasselbalch Equation for Weak Acid:
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The Henderson-Hasselbalch equation for weak acids relates the pH of a solution to the acid dissociation constant (pKa) and the concentration of the acid. This specific form is used for calculating the pH of weak acid solutions where the approximation holds true.
The calculator uses the Henderson-Hasselbalch equation for weak acids:
Where:
Explanation: This equation provides an approximation for calculating the pH of weak acid solutions, assuming the acid dissociation is minimal and the concentration of H⁺ ions comes primarily from the weak acid.
Details: Accurate pH calculation for weak acids is essential in chemistry, biochemistry, pharmaceutical formulations, and industrial processes where pH control is critical for reaction rates, stability, and biological activity.
Tips: Enter the acid dissociation constant (pKa) and the concentration of the weak acid in mol/L. Ensure all values are valid (pKa typically between 0-14, concentration > 0).
Q1: What is a weak acid?
A: A weak acid is an acid that partially dissociates in aqueous solution, unlike strong acids which completely dissociate.
Q2: When is this equation applicable?
A: This specific form is applicable for weak acids where the approximation pH = (pKa - log[HA])/2 holds, typically when the acid concentration is not too dilute.
Q3: What are typical pKa values for weak acids?
A: Common weak acids include acetic acid (pKa = 4.76), formic acid (pKa = 3.75), and carbonic acid (pKa = 6.35).
Q4: What are the limitations of this equation?
A: This approximation may not be accurate for very dilute solutions, strong acids, or when other ions significantly affect the pH.
Q5: How does temperature affect the calculation?
A: Temperature can affect both pKa values and the autoionization of water (Kw), which may influence the accuracy of pH calculations.