pKa and pKb Calculator – Convert Ka, Kb, pKa, and pKb
Convert between Ka, Kb, pKa, and pKb values effortlessly with our pKa/pKb calculator. Use the relationship pKa + pKb = 14 to find acid and base dissociation constants. Essential for acid-base chemistry and biochemistry.
pKa and pKb are logarithmic measures of acid and base strength. Lower pKa values indicate stronger acids. Lower pKb values indicate stronger bases.
Formulas
Acid Strength Guide
| pKa Range | Acid Strength | Example |
|---|---|---|
| < 0 | Very Strong | HCl (-7) |
| 0-3 | Strong | H₃PO₄ (2.1) |
| 3-7 | Moderate | Acetic acid (4.76) |
| 7-14 | Weak | NH₄⁺ (9.25) |
| > 14 | Very Weak | H₂O (15.7) |
Example: Acetic Acid
Ka = 1.8 × 10⁻⁵
pKa = -log₁₀(1.8 × 10⁻⁵) = 4.74
pKb = 14 - 4.74 = 9.26
Enter values and calculate to see the graph
| Acid | Formula | pKa | Ka |
|---|---|---|---|
| Hydrochloric | HCl | -7 | 10⁷ |
| Acetic | CH₃COOH | 4.76 | 1.8 × 10⁻⁵ |
| Carbonic | H₂CO₃ | 6.35 | 4.5 × 10⁻⁷ |
| Ammonium | NH₄⁺ | 9.25 | 5.6 × 10⁻¹⁰ |
| Water | H₂O | 15.7 | 2 × 10⁻¹⁶ |
Choose your conversion type
Select from Ka to pKa, pKa to Ka, Kb to pKb, pKb to Kb, or pKa-pKb interconversion.
Enter your value
Input the dissociation constant or p-value. Use scientific notation for Ka/Kb (e.g., 1.8e-5).
Get instant results
View the converted value plus a graph showing the relationship between parameters.
Six conversion modes
Handle any Ka, Kb, pKa, or pKb conversion in one tool.
Visual relationship graphs
See how Ka and pKa relate across different values.
Acid strength reference
Built-in table classifies acids from very strong to very weak.
Common pKa values
Quick lookup table for HCl, acetic acid, carbonic acid, and more.
Scientific notation support
Enter values like 1.8e-5 directly without manual conversion.
What is the formula for pKa?
pKa = -log10(Ka). For acetic acid with Ka = 1.8 × 10^-5, pKa = -log10(1.8 × 10^-5) = 4.74.
How do you convert pKa to pKb?
Use pKa + pKb = 14 at 25°C. If pKa = 4.76, then pKb = 14 - 4.76 = 9.24.
What does a low pKa value mean?
Low pKa indicates a strong acid that dissociates completely. pKa less than 0 means very strong acid like HCl.
What is Ka in chemistry?
Ka is the acid dissociation constant. It measures how much an acid dissociates in water. Higher Ka means stronger acid.
Why is pKa + pKb = 14?
This comes from Kw = [H+][OH-] = 10^-14 at 25°C. Taking -log of both sides gives pKa + pKb = 14.
Try our other chemistry tools: the pH calculator for acid-base calculations, the Henderson-Hasselbalch calculator for buffer solutions, and the titration calculator for neutralization problems.
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