Acids, Bases and the pH Scale Explained
Acids and bases are everywhere — in your stomach, your soap, and your food. Chemists measure how acidic or basic something is using the pH scale.
What acids and bases are
An acid releases hydrogen ions (H⁺) when dissolved in water. A base does the opposite — it accepts hydrogen ions, often releasing hydroxide ions (OH⁻). When an acid and a base react, they neutralise each other and usually form water and a salt.
The pH scale
pH runs from 0 to 14. The lower the number, the more acidic; the higher, the more basic (alkaline). Each step is ten times stronger than the next, because the scale is logarithmic.
- •pH below 7: acidic (lemon juice ≈ 2, vinegar ≈ 3).
- •pH 7: neutral (pure water).
- •pH above 7: basic (baking soda ≈ 9, bleach ≈ 13).
How we measure it
Indicators change colour at different pH values — litmus paper turns red in acid and blue in base. Universal indicator and pH meters give a more precise reading.
Frequently asked questions
What is a neutral pH?
A pH of 7, like pure water — neither acidic nor basic.
Is a lower pH more acidic?
Yes. The lower the pH number, the more acidic the substance.
What happens when an acid meets a base?
They neutralise each other, typically forming water and a salt.