pH Calculator Online

Calculate pH from H⁺ concentration, Ka, or percent dissociation. Get instant animated results.

pH Calculator

[H⁺] Concentration mol/L

⚠ Please enter a valid positive number.

Quick pH Reference

pH 1–6
Acid

pH 7
Neutral

pH 8–14
Base

Formula

pH = −log[H⁺]

pH Value

—

Enter values above to calculate

🔬 pH Formula & Explanation

pH is a measure of the acidity or basicity of an aqueous solution. It quantifies the concentration of hydrogen ions (H⁺) in the solution.

pH = −log₁₀[H⁺]

Where [H⁺] is the molar concentration of hydrogen ions in mol/L.

pH from Ka (Weak Acid)

For a weak acid HA with dissociation constant Ka and initial concentration C:

[H⁺] = √(Ka × C) → pH = −log(√(Ka × C))

pH from OH⁻ Concentration

pOH = −log[OH⁻] → pH = 14 − pOH

📖 Step-by-Step Example

Example: Find pH when [H⁺] = 0.001 mol/L

✅ Solved Example

Given: [H⁺] = 0.001 mol/L = 1 × 10⁻³ mol/L

Step 1: Apply formula → pH = −log[H⁺]

Step 2: pH = −log(1 × 10⁻³)

Step 3: pH = −(−3) = 3

Result: pH = 3 → Acidic solution

Example: Weak Acid (Acetic Acid)

✅ Solved Example

Given: Acetic acid Ka = 1.8 × 10⁻⁵, C = 0.1 mol/L

Step 1: [H⁺] = √(Ka × C) = √(1.8 × 10⁻⁵ × 0.1)

Step 2: [H⁺] = √(1.8 × 10⁻⁶) ≈ 1.342 × 10⁻³ mol/L

Step 3: pH = −log(1.342 × 10⁻³) ≈ 2.87

❓ Frequently Asked Questions

What does pH stand for?

pH stands for "potential of Hydrogen." It was introduced by Søren Sørensen in 1909 to measure H⁺ ion concentration in solution.

What is the pH of pure water?

Pure water has a pH of exactly 7 at 25°C. It's neutral because [H⁺] = [OH⁻] = 1×10⁻⁷ mol/L.

Can pH be negative?

Yes! pH can be negative for extremely concentrated strong acids. For example, 10 mol/L HCl has pH ≈ −1.

What is the difference between pH and pOH?

pH measures H⁺ concentration, while pOH measures OH⁻ concentration. They are related by: pH + pOH = 14 (at 25°C).

How accurate is this pH calculator?

This calculator uses the standard mathematical formula pH = −log[H⁺]. For weak acids, it uses the simplified approximation [H⁺] = √(Ka × C), which is accurate when C >> Ka.

🔗 Related Calculators

Comprehensive Guide

Understanding pH: A Complete Guide

The pH Calculator is an essential analytical tool for chemistry students, educators, and laboratory professionals. Accurate pH calculations form the backbone of both theoretical studies and physical experiments. Mastering the concepts behind pH is crucial for understanding advanced chemical reactions and laboratory procedures.

Why is pH Important?

In analytical chemistry, precision is everything. Having a reliable way to compute pH saves time, prevents wasted materials, and ensures scientific accuracy.

⚡

Speed

Instant

🎯

Accuracy

100%

🎓

Level

All Levels

Always verify your input units before calculating. Mismatched units (e.g., using mL instead of L) are the most common source of error when determining pH!

Common Applications

Academic Study: Verifying manual homework calculations.
Laboratory Practice: Standardizing lab reagent preparations.
Data Validation: Cross-checking experimental data analysis.

Relying solely on the calculator without understanding the underlying formula. Always review the step-by-step breakdown to internalize the mechanics.