Water - Ionization Constant, pKw, of Normal and Heavy Water
Water ionization constant (pKw) values for normal water (H2O) and heavy water (D2O) at various temperatures. The data shows how pKw varies with temperature in both Celsius and Fahrenheit scales.
Water Ionization Constant (pKw)
The water ionization constant, pKw, represents the autoprotolysis of water:
2 H₂O ↔ H₃O⁺ + OH⁻
The equilibrium constant is defined as:
Kw = (H₃O⁺)(OH⁻)
Where (H₃O⁺) and (OH⁻) represent the concentrations of hydronium and hydroxide ions respectively.
Key Points:
- pKw varies with temperature: The standard value of 1.00×10⁻¹⁴ (pKw = 14) applies at 25°C
- Heavy Water (D₂O): Self-ionizes less than normal water, resulting in larger pKw values
- Ion Concentrations: Since H₃O⁺ and OH⁻ are produced in a 1:1 molar ratio: (H₃O⁺) = (OH⁻) = √Kw
- Temperature Dependence: pKw decreases as temperature increases for both H₂O and D₂O