pH definition Calculator

Formula first

Overview

The pH scale measures the acidity or alkalinity of an aqueous solution by calculating the negative base-10 logarithm of the molar concentration of hydrogen ions. It provides a manageable numerical range, typically from 0 to 14, representing the inverse relationship between hydrogen ion concentration and the degree of acidity.

Symbols

Variables

[H^+] = Hydrogen Ion Concentration, pH = pH Value

Apply it well

When To Use

When to use: Use this equation when working with dilute aqueous solutions to quantify acidity or basicity. It assumes that the molar concentration of hydrogen ions is approximately equal to their thermodynamic activity, which is most accurate for concentrations below 1.0 M.

Why it matters: This scale is crucial for chemistry, biology, and environmental science because even small shifts in H⁺ concentration can denature proteins, alter chemical reaction rates, or impact aquatic life. It simplifies exponential concentration values into a linear scale that is easier to communicate and interpret.

Avoid these traps

Common Mistakes

• Forgetting the negative sign.
• Using ln instead of log10.

One free problem

Practice Problem

A sample of hydrochloric acid has [H+] = 0.04 mol/$d{m}^3$. Calculate the pH of this solution to 2 decimal places.

Solve for: $pH$

Hint: pH = -log10[H+]. Use a scientific calculator.

The full worked solution stays in the interactive walkthrough.

Keep going

Related Formulas

References

Sources

1. Atkins' Physical Chemistry
2. IUPAC Gold Book: pH
3. Wikipedia: pH
4. Atkins' Physical Chemistry (11th ed.)
5. IUPAC Gold Book: 'pH'
6. Wikipedia: 'pH'
7. AQA A-Level Chemistry — Acids and Bases