1. What is the Henderson-Hasselbalch Equation?

The Henderson-Hasselbalch equation relates pH, pKa, and the ratio of concentrations of a weak acid and its conjugate base in solution. It's particularly useful in chemistry and biochemistry for buffer preparation and understanding acid-base behavior.

2. How Does the Calculator Work?

The calculator uses the Henderson-Hasselbalch equation:

Where:

• \( pKa \) — Acid dissociation constant (dimensionless)
• \( pH \) — Solution pH (dimensionless)
• \( [base] \) — Concentration of conjugate base (mol/L)
• \( [acid] \) — Concentration of weak acid (mol/L)

Explanation: The equation shows that when the concentrations of acid and base are equal, the pKa equals the pH.

3. Importance of pKa Calculation

Details: Knowing pKa is essential for predicting the ionization state of molecules at different pH values, which affects solubility, absorption, and biological activity.

4. Using the Calculator

Tips: Enter pH value, base concentration, and acid concentration. All concentrations must be positive values in mol/L.

5. Frequently Asked Questions (FAQ)

Q1: What is the relationship between pKa and pH?
A: pKa is the pH at which half of the acid molecules are deprotonated. When pH = pKa, [base] = [acid].

Q2: What are typical pKa values?
A: For most organic acids, pKa ranges from 2-20. Strong acids have low pKa values (<0), while strong bases have high pKa values (>14).

Q3: When is the Henderson-Hasselbalch equation valid?
A: It's valid for dilute solutions (≤0.1M) where activity coefficients are close to 1, and for weak acids (pKa > 2).

Q4: How does temperature affect pKa?
A: pKa values are temperature-dependent. Most are reported at 25°C, and can change by 0.01-0.1 units per °C.

Q5: Can I use molarity or molality for concentrations?
A: For dilute aqueous solutions at constant temperature, molarity (mol/L) is typically used and sufficient.