Henderson-Hasselbalch Buffer Calculator
pH of a buffer from its pKa and the ratio of conjugate base to weak acid.
Results
pH
4.7600
Ratio
1.00000
Acid dissociation constant
0.000017378008
H⁺ concentration
0.000017378008
mol/L
What this tool does
When the two concentrations are equal the pH simply equals the pKa, and that is where a buffer resists change best. The useful range runs about one pH unit either side, because beyond a ten-to-one ratio there is too little of one partner left to absorb anything. Acetic acid has a pKa of 4.76; carbonic acid 6.35; dihydrogen phosphate 7.20.
Formula
pH = pKa + log₁₀([A⁻] ÷ [HA])
Variables
| Symbol | Meaning | Unit |
|---|---|---|
pk | pKa | — |
cb | Conjugate base concentration | mol/L |
ca | Weak acid concentration | mol/L |
PH | pH | — |
RT | Ratio | — |
KA | Acid dissociation constant | — |
HC | H⁺ concentration | mol/L |
Worked example
- pKa4.76
- Conjugate base concentration0.1 mol/L
- Weak acid concentration0.1 mol/L
- pH4.7600
- Ratio1.00000
- Acid dissociation constant0.000017378008
- H⁺ concentration0.000017378008 mol/L
Limitations
- For work that must comply with a standard or be signed off, check the result against the applicable code and have it reviewed by a qualified engineer.
- The formula assumes ideal conditions: no friction losses, no air resistance and no efficiency losses unless you enter them.