Dissociation Constant of Water
As a frequently used special case, the dissociation constant of water is often expressed as Kw:
The concentration of water is not included in the definition of Kw, for reasons described in the article equilibrium constant.
The value of Kw varies with temperature, as shown in the table below. This variation must be taken into account when making precise measurements of quantities such as pH.
| Water temperature | Kw / 10−14 | pKw |
|---|---|---|
| 0°C | 0.1 | 14.92 |
| 10°C | 0.3 | 14.52 |
| 18°C | 0.7 | 14.16 |
| 25°C | 1.2 | 13.92 |
| 30°C | 1.8 | 13.75 |
| 50°C | 8.0 | 13.10 |
| 60°C | 12.6 | 12.90 |
| 70°C | 21.2 | 12.67 |
| 80°C | 35 | 12.46 |
| 90°C | 53 | 12.28 |
| 100°C | 73 | 12.14 |
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