# pH scale

A scale from 0 to 14 showing how acidic or alkaline a solution is. Below 7 is acid, 7 is neutral and above 7 is alkaline.

Chemistry (school) · Part 06: Acids, bases and salts · Card 3 of 9 · Last updated 2026-10-19

## Analogy

Like a temperature scale for acidity, with 7 in the middle as normal.

## Example

**Everyday pH**

Stomach acid: 1
Lemon juice: 2
Pure water: 7
Bleach: 12

## In practice

Pure water is pH 7. Lemon juice is about 2. Soap is about 10.

## Practice

### Flashcards

- **What is the pH of a neutral solution?** 7.

## Questions people ask

### What does each step on the pH scale mean?

Each step is a tenfold change in acidity. A solution with pH 3 is ten times more acidic than one with pH 4, and one hundred times more than pH 5. That is why a small change in the number is a big change in the chemistry.

### How do you measure pH accurately?

A pH meter with a probe gives a precise number, while universal indicator paper or solution gives a rough value by colour. Indicator colours can be hard to judge in coloured solutions, so a meter is better for exact work and for experiments with several steps.

## Related concepts

- [Indicator](https://studyvisually.com/learn/science/chemistry-school/chemistry-school-part-6/chemistry-school-part-6-concept-4)

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