PH to PKA
Convert pH into pKa by adding the conjugate-base to acid ratio used in the Henderson-Hasselbalch relationship.
This converter uses the Henderson-Hasselbalch relationship. You must supply the conjugate base to acid ratio because pH alone is not enough to determine pKa.
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Conversion Examples
PH to PKA Table (Ratio 1 Example)
| pH | [A-]/[HA] Ratio | pKa |
|---|---|---|
| 2 | 1 | 2 |
| 3 | 1 | 3 |
| 4 | 1 | 4 |
| 5 | 1 | 5 |
| 6 | 1 | 6 |
| 7 | 1 | 7 |
| 8 | 1 | 8 |
| 9 | 1 | 9 |
| 10 | 1 | 10 |
| 12 | 1 | 12 |
Popular Conversions
- pH 3 with ratio 1 = 3 pKa
- pH 4 with ratio 1 = 4 pKa
- pH 5 with ratio 1 = 5 pKa
- pH 6 with ratio 1 = 6 pKa
- pH 7 with ratio 1 = 7 pKa
- pH 8 with ratio 1 = 8 pKa
- pH 9 with ratio 1 = 9 pKa
- pH 10 with ratio 1 = 10 pKa
What is pH and pKa?
pH
Definition: pH is a logarithmic way to express hydrogen ion activity, and in routine solution work it is often approximated from hydrogen ion concentration.
History/origin: The pH concept standardized acid-base measurement and comparison across chemistry and laboratory science.
Current use: PH is used in water testing, buffers, titrations, clinical labs, food science, and many chemical processes.
pKa
Definition: pKa is the negative base-10 logarithm of Ka and gives a compact way to compare acid strength.
History/origin: It followed the success of pH notation and made acid strength values easier to read and compare.
Current use: PKa is used in buffer design, medicinal chemistry, acid-base prediction, and equilibrium calculations.
Related Acid-Base Relationships
Acid-base conversions often connect logarithmic quantities, equilibrium constants, and concentration terms.
| Related Conversion | Factor or Rule | Formula |
|---|---|---|
| pH to H+ | 10-pH | [H+] = 10-pH |
| pKa to Ka | 10-pKa | Ka = 10-pKa |
| pH to pKa | needs base/acid ratio | pKa = pH – log([A-]/[HA]) |
| pKa to pH | needs base/acid ratio | pH = pKa + log([A-]/[HA]) |
| pH to Ka | needs initial acid concentration | Ka = [H+]2 ÷ (C – [H+]) |
| Molarity to molality | needs density and MW | m = 1000M ÷ (1000d – MWM) |
| Molality to molarity | needs density and MW | M = 1000md ÷ (1000 + mMW) |
| Molarity to ppm | dilute aqueous approximation | ppm ≈ M × MW × 1,000 |
Typical Use Cases
Frequently Asked Questions
Q: Why is a ratio field required here?
A: PH alone does not determine pKa, and pKa alone does not determine pH. The Henderson-Hasselbalch relationship needs the conjugate base to acid ratio as the second input.
Q: What does a ratio of 1 mean?
A: A ratio of 1 means [A-] equals [HA], so pH and pKa are equal in the Henderson-Hasselbalch approximation.
Q: Can I use ratios below 1?
A: Yes. Ratios smaller than 1 mean there is more acid form than base form, which lowers pH relative to pKa or raises pKa relative to pH in the reverse setup.
Q: Is this exact for every buffer?
A: It is a standard approximation that works best when the buffer pair behaves ideally and the Henderson-Hasselbalch form is appropriate.
Q: Why does the table use a ratio of 1?
A: A ratio of 1 makes the table easy to scan because pH and pKa become the same. Change the ratio field above for your actual buffer mixture.
Q: When is this useful?
A: It is useful in buffer preparation, acid-base teaching, and quick checks of conjugate acid-base pair relationships.
References
- International Union of Pure and Applied Chemistry. Gold Book: pH. https://goldbook.iupac.org/terms/view/P04524.html
- International Union of Pure and Applied Chemistry. Gold Book: acid dissociation constant. https://goldbook.iupac.org/terms/view/15441