A weak base only partially dissociates in water, making its pH harder to calculate by hand — the Weak Base pH Calculator does the math for you. Enter your Base Concentration (in mol/L) and Base Dissociation Constant (Kb) to get the solution's pH as the primary output. Secondary results include pOH, Hydroxide Ion Concentration, and Hydrogen Ion Concentration.
pH
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pOH
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Hydroxide Ion Concentration
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Hydrogen Ion Concentration
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A weak base is a substance that only partially ionizes in aqueous solution, releasing fewer hydroxide ions compared to strong bases. Unlike strong bases that completely dissociate, weak bases establish an equilibrium between ionized and non-ionized forms, characterized by their Kb value.
Kb values for common weak bases can be found in chemistry reference tables or databases. For ammonia (NH₃), Kb = 1.8 × 10⁻⁵. If you only have pKb, convert using Kb = 10⁻ᵖᴷᵇ.
Weak bases don't completely ionize, so you can't simply use the base concentration to find [OH⁻]. Instead, you must use the Kb expression and solve the equilibrium equation to determine the actual hydroxide ion concentration.
In any aqueous solution at 25°C, pH + pOH = 14. For weak bases, you first calculate pOH from the hydroxide ion concentration, then subtract from 14 to get pH.
Use the format 1E-5 for 1 × 10⁻⁵. For example, enter 1.8E-5 for ammonia's Kb value of 1.8 × 10⁻⁵. The calculator accepts both decimal and scientific notation formats.
Common weak base concentrations range from 0.001 M to 1.0 M. Very dilute solutions (< 0.001 M) may require consideration of water's autoionization, while very concentrated solutions may show non-ideal behavior.
This calculator is designed for monoprotic weak bases (bases that accept one proton). For polyprotic bases like carbonate ion, you would need to consider multiple Kb values and use more complex equilibrium calculations.