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Henderson-Hasselbalch Equation:
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The Henderson-Hasselbalch equation relates the pH of a solution to the pKa (acid dissociation constant) and the ratio of the concentrations of the conjugate base and weak acid in a buffer solution. It's fundamental in chemistry and biochemistry for preparing buffer solutions.
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 base to acid concentrations.
Details: Buffer solutions resist changes in pH when small amounts of acid or base are added. They're essential in biological systems, chemical processes, and laboratory work where maintaining stable pH is crucial.
Tips: Enter the pKa value of your weak acid, the concentration of the conjugate base, and the concentration of the weak acid. All concentrations must be in the same units (mol/L).
Q1: What is the valid range for this equation?
A: The equation works best when the pH is within ±1 unit of the pKa (the buffer's effective range).
Q2: Can I use molar ratios instead of concentrations?
A: Yes, since the equation uses a ratio, you can use either concentrations or amounts (moles) as long as both base and acid are in the same units.
Q3: What are common buffer systems?
A: Common systems include acetic acid/acetate (pKa 4.76), phosphate (pKa 7.21), and Tris (pKa 8.07).
Q4: When does this equation not apply?
A: The equation may not be accurate for very dilute solutions (<1 mM) or very strong acids/bases.
Q5: How can I prepare a buffer of specific pH?
A: Choose an acid with pKa close to your desired pH, then use this calculator to determine the needed base/acid ratio.