Acids and Bases: Understanding pH, Neutralisation, and Indicators

Acids and bases are a central topic in chemistry — and we encounter them everywhere in daily life.

What Are Acids?

Acids are substances that release H⁺ ions (protons) in water. Examples: Hydrochloric acid (HCl), Sulphuric acid (H₂SO₄), Acetic acid, Citric acid.

What Are Bases?

Bases accept H⁺ ions or release OH⁻ ions. Examples: Sodium hydroxide (NaOH), Potassium hydroxide (KOH), Ammonia (NH₃).

The pH Scale

The pH value indicates how acidic or basic a solution is. Scale from 0 to 14: pH 0-6 = acidic, pH 7 = neutral, pH 8-14 = basic. Each pH step means a 10-fold change! pH 3 is 100 times more acidic than pH 5.

Neutralisation

When an acid and a base meet, they neutralise each other: Acid + Base → Salt + Water. HCl + NaOH → NaCl + H₂O.

Everyday Examples

Stomach acid: pH 1-2. Cola: pH 2.5. Tap water: pH 7. Soap: pH 9-10. Drain cleaner: pH 13-14. When you take an antacid for heartburn, that's neutralisation!