pKa Calculator
Convert acid dissociation constant (Ka) to pKa
Example: 1.75e-5 for Acetic Acid
✅ What This Calculator Is & Why It Matters
The pKa Calculator determines the acid dissociation constant (pKa) from the equilibrium concentrations of the acid and its conjugate base, or by converting directly from the Ka value.
Why does pKa matter? The pKa value is the definitive measure of acid strength. A lower pKa means a stronger acid. It is crucial for predicting buffer capacity in biochemistry and determining the protonation state of drugs at physiological pH.
✅ The Formula Explained Simply
The pKa is simply the negative base-10 logarithm of the acid dissociation constant (Ka):
pKa = -log₁₀(Ka)
Alternatively, derived from the Henderson-Hasselbalch equation:
pKa = pH - log([A⁻]/[HA])
✅ 3-5 Real-World Examples
Example 1: Acetic Acid
The Ka of acetic acid is 1.76 × 10⁻⁵.
Result: pKa = -log(1.76 × 10⁻⁵) = 4.75.
Example 2: Formic Acid
The Ka of formic acid is 1.77 × 10⁻⁴.
Result: pKa = 3.75. (Notice it is a stronger acid than acetic acid).
✅ FAQ Section (Google PAA Targeted)
What does a negative pKa mean?
A negative pKa indicates a very strong acid (like HCl or H₂SO₄) that completely dissociates in water. The equilibrium heavily favors the products.
How does pKa relate to pH?
pKa is a property of the molecule itself, while pH is a property of the solution. When the pH of a solution equals the pKa of the dissolved acid, the acid is exactly 50% dissociated.
✅ Pro-Tips for pKa Calculations
- Buffer Regions: A weak acid makes an excellent buffer in the pH range of its pKa ± 1.
- Polyprotic Acids: Remember that acids with multiple protons (like phosphoric acid, H₃PO₄) have multiple pKa values, one for each deprotonation step.
✅ Related Calculators
✅ AI Explanation of Results
Our AI cross-references the calculated pKa against physiological pH (7.4) and tells you what percentage of the molecule will be ionized in the human bloodstream.
About the pKa Calculator
Calculate pH, pKa, buffer capacity, or titration values using the Henderson-Hasselbalch equation. Accurate chemical equilibrium tool.
This precision chemistry tool is designed for academic reference, laboratory workflows, and student education. It provides instant, real-time computational results with standard formulas and dimensional analysis inputs.