Acids & Bases
Testing for acids and bases, pH scale, neutralisation
Acids and Bases
Acids are substances that taste sour (like lemon juice and vinegar) and have a pH below 7. Bases taste bitter and feel slippery (like soap) and have a pH above 7. A pH of 7 is neutral — like pure water.
The pH Scale
The pH scale runs from 0 to 14:
• 0–6: Acidic (lower number = stronger acid)
• 7: Neutral
• 8–14: Basic/alkaline (higher number = stronger base)
We use indicators like litmus paper or universal indicator to test pH. Acids turn litmus red; bases turn it blue.
Example
Everyday Examples
Acids: lemon juice (pH 2), vinegar (pH 3), cold drink (pH 3)
Neutral: pure water (pH 7)
Bases: baking soda (pH 9), soap (pH 10), bleach (pH 13)
Neutralisation: acid + base → salt + water
Example: stomach acid + antacid tablet → relief!
Note
Safety Warning
Strong acids and bases are dangerous — they can burn skin. In the lab, always wear safety goggles and gloves. Never taste chemicals! Use indicators to test safely.
Key Vocabulary
AcidA substance with a pH below 7 that tastes sour
BaseA substance with a pH above 7 that tastes bitter
pH scaleA scale from 0 to 14 measuring how acidic or basic a substance is
NeutralNeither acidic nor basic, with a pH of 7
IndicatorA substance that changes colour to show if something is acid or base
NeutralisationA reaction between an acid and a base to form salt and water
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