Activity Coefficient Calculator
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Activity Coefficient Formula
The ionic strength and charge number of ions are the two significant factors that determine the activity coefficient of an ion in a dilute solution.
Debye-Hückel Limiting Law
log γ = -A z² √I
where:
- γ – Activity coefficient
- A – Debye-Hückel constant (typically 0.509 for water at 25°C)
- z – Charge number of the ion
- I – Ionic strength (mol/L)
Example Calculation
For a 0.001 M NaCl solution (I = 0.001) with z = 1:
log γ = -0.509 × (1)² × √0.001
log γ = -0.509 × 0.0316 = -0.0161
γ = 10-0.0161 = 0.964
This shows the ion activity is about 96.4% of its concentration.
How to Use This Calculator
- Enter the ionic strength of your solution (typically 0-0.01 M for best results)
- Input the charge number of the ion (e.g., 1 for Na⁺, 2 for Ca²⁺)
- Keep or adjust the Debye-Hückel constant (default 0.509 for water at 25°C)
- Click calculate to get the activity coefficient
Important Parameters
| Parameter | Symbol | Typical Values |
|---|---|---|
| Ionic Strength | I | 0.001 - 0.01 M (for most accurate results) |
| Charge Number | z | 1, 2, 3 (for common ions) |
| Debye-Hückel Constant | A | 0.509 (water, 25°C) |