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Chemistry Acids, bases and salts
Class 6 Beginner About 15 min Free

Natural indicators: acids and bases

Use red cabbage indicator to sort everyday liquids into acids, bases and neutral substances.

Core concept

In short: Mix red cabbage juice with liquids and use its colour to tell acids from bases.

Indicators change colour in acids and bases

Topic: Acids, bases and salts

Some substances are acid: A substance that tastes sour, like lemon juice or vinegar. It turns blue litmus red. All key words, some are basic and some are neutral: Neither an acid nor a base, like pure water. All key words. An indicator: A substance that changes colour to show whether something is an acid or a base. All key words is a substance that changes colour depending on which of these it is mixed with. Red cabbage juice is a natural indicator. It is purple on its own.

Key words explained

What you will learn

  • Describe what an indicator is.
  • Use red cabbage indicator to identify acidic, basic and neutral substances.
  • Record observations as evidence for a conclusion.

Before you start

  • Know how to measure a liquid in millilitres (mL).

Materials

  • Red cabbage indicator
  • Lemon juice
  • Distilled water
  • Baking soda solution

Equipment

  • 3 beakers (50 mL)
  • Stirring rod

Procedure

  1. Add 10 mL of red cabbage indicator to each beaker.
  2. Add one test liquid to each beaker: lemon juice, distilled water or baking soda solution.
  3. Stir each beaker.
  4. Write down the colour you see in each beaker.

How this simulation is simplified

  • Colours are simplified to three groups. Real red cabbage indicator shows a range of colours from red to yellow-green.
  • Mixing is instant once you stir.
Bench