pH Calculator

Calculate pH, pOH, H⁺ concentration, or OH⁻ concentration. Enter any one value to calculate all related values. Includes temperature correction.

Solve For

H⁺ Concentration (M)

pOH

OH⁻ Concentration (M)

Temperature (°C)

Core Formulas: pH = -log₁₀[H⁺] [H⁺] = 10⁻ᵖᴴ pOH = -log₁₀[OH⁻] [OH⁻] = 10⁻ᵖᴼᴴ Relationship at 25°C: pH + pOH = 14 [H⁺] × [OH⁻] = Kw = 10⁻¹⁴ Derived: pOH = 14 - pH pH = 14 - pOH [OH⁻] = 10⁻¹⁴ ÷ [H⁺] [H⁺] = 10⁻¹⁴ ÷ [OH⁻] pH Scale: • pH < 7: Acidic (more H⁺) • pH = 7: Neutral • pH > 7: Basic/Alkaline (more OH⁻)

Example 1 (Strong Acid): 0.01 M HCl (complete dissociation) [H⁺] = 0.01 M = 1×10⁻² M pH = -log₁₀(0.01) = 2.00 pOH = 14 - 2 = 12.00 [OH⁻] = 1×10⁻¹² M Example 2 (Neutral Water): Pure water at 25°C pH = 7.00 [H⁺] = 10⁻⁷ M = 0.0000001 M [OH⁻] = 10⁻⁷ M = 0.0000001 M pOH = 7.00 Example 3 (Strong Base): 0.001 M NaOH [OH⁻] = 0.001 M = 1×10⁻³ M pOH = -log₁₀(0.001) = 3.00 pH = 14 - 3 = 11.00 [H⁺] = 1×10⁻¹¹ M Example 4 (Blood pH): Human blood: pH = 7.40 [H⁺] = 10⁻⁷·⁴⁰ = 3.98×10⁻⁸ M = 39.8 nM pOH = 14 - 7.40 = 6.60 [OH⁻] = 2.51×10⁻⁷ M Example 5 (Stomach Acid): Gastric juice: pH ≈ 2.00 [H⁺] = 0.01 M This is 100,000 times more acidic than neutral water!

What is pH?

pH is a measure of hydrogen ion (H⁺) concentration in a solution. pH = -log₁₀[H⁺]. The pH scale ranges from 0-14, where pH 7 is neutral, pH < 7 is acidic, and pH > 7 is basic (alkaline). Each pH unit represents a 10-fold change in H⁺ concentration.

What is the relationship between pH and pOH?

pH + pOH = 14 (at 25°C). pOH = -log₁₀[OH⁻]. If you know pH, you can find pOH and vice versa. For example, pH 3 means pOH = 11. This relationship comes from the water equilibrium constant Kw = [H⁺][OH⁻] = 10⁻¹⁴.

How do I calculate pH from H⁺ concentration?

Use pH = -log₁₀[H⁺]. For example, if [H⁺] = 1×10⁻³ M, then pH = -log₁₀(0.001) = 3. Remember that lower pH means higher H⁺ concentration.

How do I calculate H⁺ from pH?

Use [H⁺] = 10⁻ᵖᴴ. For example, if pH = 5, then [H⁺] = 10⁻⁵ = 0.00001 M = 10 µM. This is the inverse operation of taking the logarithm.

What are common pH values?

Stomach acid: pH ~2, Lemon juice: pH ~2-3, Vinegar: pH ~2.5, Coffee: pH ~5, Pure water: pH 7, Blood: pH 7.4, Baking soda: pH ~9, Bleach: pH ~12-13. These values show the wide range of pH in everyday substances.

Why is pH important?

pH affects chemical reactions, enzyme activity, solubility, and biological processes. Most enzymes work only in narrow pH ranges. Biological systems use buffers to maintain stable pH. For example, human blood must stay near pH 7.4 for proper function.

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