pKa to pH Calculator
The pKa to pH converter precisely determines the pH of buffer solutions by incorporating the Henderson-Hasselbalch equation, considering both the acid dissociation constant (Ka) and the concentration ratios of conjugate acid-base pairs.
When analyzing acetic acid (CH₃COOH) with a pKa of 4.76, the pKa to pH conversion tool can compute that at equal concentrations of acid and conjugate base, the pH equals the pKa, making pH = 4.76.
pKa to pH Formula
The conversion relies on the Henderson-Hasselbalch equation:
pH = pKa + log([A⁻]/[HA])where [A⁻] represents the conjugate base concentration and [HA] denotes the weak acid concentration.
Consider a buffer solution containing benzoic acid (pKa = 4.2):
If [A⁻] = 0.15M and [HA] = 0.25M, applying the formula yields:
pH = 4.2 + log(0.15/0.25) = 4.0Formic Acid Buffer Analysis:
Given: pKa = 3.75, [HCOOH] = 0.3M, [HCOO⁻] = 0.2M pH calculation: 3.75 + log(0.2/0.3) = 3.62Phosphate Buffer System:
Given: pKa = 7.21, [H₂PO₄⁻] = 0.4M, [HPO₄²⁻] = 0.6M pH calculation: 7.21 + log(0.6/0.4) = 7.39pKa to pH Conversion Table
| pKa | [A⁻]/[HA] Ratio | Log([A⁻]/[HA]) | pH |
|---|---|---|---|
| 3.5 | 0.01 | -2.0 | 1.5 |
| 3.5 | 0.1 | -1.0 | 2.5 |
| 3.5 | 1.0 | 0.0 | 3.5 |
| 3.5 | 10.0 | +1.0 | 4.5 |
| 3.5 | 100.0 | +2.0 | 5.5 |
| 4.0 | 0.01 | -2.0 | 2.0 |
| 4.0 | 0.1 | -1.0 | 3.0 |
| 4.0 | 1.0 | 0.0 | 4.0 |
| 4.0 | 10.0 | +1.0 | 5.0 |
| 4.0 | 100.0 | +2.0 | 6.0 |
| 8.0 | 0.01 | -2.0 | 6.0 |
| 8.0 | 0.1 | -1.0 | 7.0 |
| 8.0 | 1.0 | 0.0 | 8.0 |
| 8.0 | 10.0 | +1.0 | 9.0 |
| 8.0 | 100.0 | +2.0 | 10.0 |
| 9.0 | 0.01 | -2.0 | 7.0 |
| 9.0 | 0.1 | -1.0 | 8.0 |
| 9.0 | 1.0 | 0.0 | 9.0 |
| 9.0 | 10.0 | +1.0 | 10.0 |
| 9.0 | 100.0 | +2.0 | 11.0 |
| 10.0 | 0.01 | -2.0 | 8.0 |
| 10.0 | 0.1 | -1.0 | 9.0 |
| 10.0 | 1.0 | 0.0 | 10.0 |
| 10.0 | 10.0 | +1.0 | 11.0 |
| 10.0 | 100.0 | +2.0 | 12.0 |
How to convert pKa to pH?
Begin by identifying the pKa value and determining concentrations of both acid and conjugate base forms. Then apply the Henderson-Hasselbalch equation, considering temperature effects and ionic strength when necessary.
Using ammonia (NH₃):
pKa value = 9.25 Concentration values: [NH₄⁺] = 0.8M, [NH₃] = 0.4M Final pH = 9.25 + log(0.4/0.8) = 8.95Aspirin (pKa = 3.5) exhibits different absorption rates in the stomach (pH ≈ 2) versus the small intestine (pH ≈ 6), demonstrating the practical importance of understanding both pH and pKa in real-world applications.
What is difference between pH and pKa?
While interconnected, pH and pKa serve distinct roles in acid-base chemistry. pH measures the hydrogen ion concentration in solution, indicating overall acidity level. In contrast, pKa represents the acid dissociation constant, revealing an acid’s strength and its tendency to donate protons.
Lactic acid (pKa = 3.86) at equal concentrations of acid and conjugate base forms a buffer solution with pH = 3.86. Changing the ratio to 2:1 (acid:base) shifts the pH value to 3.56, demonstrating how pH varies while pKa remains constant.
What is pKa and pH?
pH measurement functions as a logarithmic scale measuring hydrogen ion concentration, ranging from 0 to 14, with 7 indicating neutrality. pKa measurement represents the negative logarithm of the acid dissociation constant (Ka), indicating an acid’s strength level – lower values signify stronger acids. Together, they provide crucial information about solution behavior, buffer capacity, and molecular properties in chemical and biological systems.