Weak Base pH Calculator

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. Also try the Buffer Capacity Calculator.

M

Concentration of the weak base in mol/L (M)

Base dissociation constant - use scientific notation for small values

Results

pH

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pOH

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Hydroxide Ion Concentration

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Hydrogen Ion Concentration

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Frequently Asked Questions

What is a weak base and how does it differ from a strong base?

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. See also our Acetate Buffer Calculator.

How do I find the Kb value for a specific weak base?

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.

Why is the pH of weak bases calculated differently than strong bases?

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.

What is the relationship between pH and pOH in weak base solutions?

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. You might also find our Equivalence Point Calculator useful.

How do I enter very small Kb values in scientific notation?

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.

What concentration range is typical for weak base solutions?

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.

Can this calculator be used for polyprotic bases?

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.