🔬 pH Strong Base Calculator

Calculate pH of strong base solutions (NaOH, KOH, Ba(OH)₂…)

Base Concentration (M)

OH⁻ per formula unit

—pH

[OH⁻]—

pOH—

[H⁺]—

How to Use This Calculator

Enter the molar concentration of your strong base and select whether it releases 1 or 2 hydroxide ions per formula unit. The calculator finds [OH⁻], then converts to pOH and pH using the water equilibrium constant at 25°C.

Identify your strong base. NaOH, KOH, and LiOH each release 1 OH⁻ per formula unit. Ba(OH)₂ and Ca(OH)₂ release 2 OH⁻ per formula unit.

Enter the molar concentration. For a solution made by dissolving 4.0 g of NaOH (molar mass 40.0 g/mol) in 1 L of water, the concentration is 0.1 M.

Choose 1 or 2 from the OH⁻ dropdown based on your base formula, then click Calculate pH.

Read pH at the top. For 0.1 M NaOH, you get pH 13.00. Also check pOH and [H⁺] if you need them for a neutralisation problem.

Strong Base pH Formula

[OH⁻] = n × C (n = OH⁻ per formula unit) pOH = −log₁₀[OH⁻] pH = 14 − pOH (at 25°C)

Strong bases dissociate completely, so [OH⁻] is simply n times the molar concentration, where n is the number of hydroxide groups in the formula. You then take the negative log of [OH⁻] to get pOH, and subtract from 14 to find pH. The relationship pH + pOH = 14 holds at 25°C because the water equilibrium constant Kw = 1.0 × 10⁻¹⁴ at that temperature.

Worked Examples

0.1 M NaOH: pOH = 1.00, pH = 14 − 1pH 13.00

0.01 M KOH: pOH = 2.00, pH = 14 − 2pH 12.00

0.05 M Ba(OH)₂: [OH⁻] = 0.1 M, pOH = 1.00pH 13.00

0.001 M NaOH: pOH = 3.00, pH = 14 − 3pH 11.00

Where This Calculation Comes Up

Calculating the pH of a strong base is a standard exercise in acid-base chemistry courses. You need it when drawing a titration curve for a strong acid-strong base titration, where the initial base pH and the final pH after the equivalence point both depend on this calculation. Lab reports for any neutralisation experiment will ask you to predict the pH before mixing so you can compare theory with the measured result.

In industry, NaOH solutions are used in soap making, paper manufacturing, and drain cleaning products. Engineers must calculate the pH of these solutions to select appropriate materials for tanks and pipelines, since high-pH solutions corrode many metals and can degrade certain plastics. In water treatment plants, sodium hydroxide is added to raise pH in acidic water supplies, and operators calculate the exact dose needed to reach a target pH of around 7.5.

Frequently Asked Questions

What are strong bases?

Strong bases completely dissociate in water. Common examples: NaOH (sodium hydroxide), KOH (potassium hydroxide), LiOH, Ba(OH)₂, Ca(OH)₂ (at low concentrations).

How is pH of a strong base calculated?

[OH⁻] equals the base concentration (×2 for dihydroxy bases). pOH = −log[OH⁻]. pH = 14 − pOH.

What pH does 0.1 M NaOH have?

[OH⁻] = 0.1, pOH = 1.00, pH = 13.00.

What about Ba(OH)₂?

Ba(OH)₂ releases 2 OH⁻ per formula unit, so [OH⁻] = 2 × C. For 0.1 M Ba(OH)₂: [OH⁻] = 0.2, pH ≈ 13.30.

Why does pH + pOH = 14?

At 25°C, Kw = [H⁺][OH⁻] = 10⁻¹⁴. Taking −log of both sides gives pH + pOH = 14.