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pH Calculator

Select the calculation parameters and enter their values. The calculator will readily calculate the pH, pOH, H+, and OH- ions in an acidic or basic solution.

Concentration of an acid:

Weight

Concentration Mole:

M ▾

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pH Calculator

Use this free pH calculator to determine pH using concentration, volume, or weight methods. It helps compute pH, pOH, [H⁺], and [OH⁻] quickly.

What Is pH?

pH, or “potential of hydrogen ions,” indicates the concentration of hydrogen ions in a solution. It measures how acidic or basic a solution is.

pH Formula

pH = -log[H⁺]

Calculating Hydrogen Ion Concentration [H⁺]

[H⁺] = 10^-pH

You can also calculate pH from pOH:

pH + pOH = 14 or pH = 14 - pOH

What Is pOH?

pOH measures hydroxide ion concentration:

pOH = -log[OH⁻]

Calculating Hydroxide Ion Concentration [OH⁻]

[OH⁻] = 10^-pOH

Ionization Constants

If [H⁺] increases, the solution is acidic (pH < 7).
If [OH⁻] increases, the solution is basic (pH > 7).

Acid Dissociation:

HA ⇌ H⁺ + A⁻

Ka = [A⁻][H⁺] / [HA]

Base Dissociation:

BOH ⇌ OH⁻ + B⁺

Kb = [OH⁻][B⁺] / [BOH]

Calculating pH from Ka

Stepwise formula:

1. a₁ = Ka × Concentration

2. a₂ = √a₁

3. a₃ = log(a₂)

4. pH = -a₃

The pH Scale

pH = 7 → Neutral solution
pH > 7 → Basic solution
pH < 7 → Acidic solution

pH scale

Examples

Example 1: Find pH of 0.25 M HCl.

pH = -log[0.25] = -(-0.602) = 0.602

Example 2: 390 mL solution with 8 g NaOH. Find pH.

Moles of NaOH = 8 / 40 = 0.2 mol
Molarity = 0.2 / 0.390 ≈ 0.512 M
pOH = -log[0.512] ≈ 0.290
pH = 14 - 0.290 ≈ 13.71

How pH Calculator Works

Input:

Select the calculation method from the drop-down.
Select the type of acid or base.
Enter required parameters and units.
Click “Calculate”.

Output:

pH
pOH
[H⁺] concentration
[OH⁻] concentration
pKa for weak acids/bases

FAQs

Relationship Between pH and pOH

pH + pOH = 14. As pH increases, pOH decreases.

Relationship with Kw

At 25°C, Kw = 1 × 10⁻¹⁴. pH + pOH = 14.

Why pH + pOH = 14?

Because [H⁺][OH⁻] = Kw = 1 × 10⁻¹⁴ → -log[H⁺] - log[OH⁻] = 14

Molarity Effect on pH

Higher acidic molarity → lower pH. Higher basic molarity → higher pH.

pH of Blood

Normal blood: 7.35–7.45 (slightly basic).

pH and pOH of Pure Water

At 25°C: pH = 7, pOH = 7 (neutral).

Difference Between p and pH

“p” = power (negative log), e.g., pKa, pOH. pH specifically measures hydrogen ion concentration.

Conclusion

pH and pOH describe acidity/basicity of a solution. This guide explains definitions, formulas, and examples. A pH calculator simplifies calculation of pH, pOH, [H⁺], and [OH⁻], useful in lab experiments and analysis.

References

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