• They are cheap and readily available in our environment
• They are safe to use
• They are suitable for school experiments
• They work just like synthetic indicators found in laboratories

Materials needed

• Fresh hibiscus flowers (red or pink colour)
• Mortar and pestle
• Distilled water or clean water
• Ethanol (50% solution) - optional
• Beaker
• Dropper
• Test tubes or small clean containers
• Acid solution (lemon juice or vinegar)
• Base solution (sodium hydroxide solution or soap solution)

Procedure

1. Collect and prepare the flowers: Pick fresh hibiscus flowers and cut them into small pieces using a knife.

2. Crush the flowers: Place the cut flowers into a mortar and crush them thoroughly with the pestle until they form a soft paste.

3. Extract the pigment: Add about 20 cm³ of distilled water to the crushed flowers and continue crushing. If available, you can add a small amount of ethanol to help extract the colour better.

4. Filter the solution: Decant or filter the mixture to separate the liquid extract from the plant materials. The liquid collected is your indicator solution.

5. Test the indicator: Add a few drops of your indicator to separate test tubes containing:

   • Acidic solution (lemon juice or vinegar)
   • Basic solution (sodium hydroxide or soap solution)
   • Neutral solution (distilled water)

6. Record observations: Note the colour changes in each solution.

Expected Results

• In acidic solutions, hibiscus extract turns pink or red
• In basic solutions, hibiscus extract turns greenish-yellow or green
• In neutral solutions, the colour remains relatively unchanged (often purplish)

Cassava leaves contain anthocyanins that can also act as natural pH indicators.

Materials needed

• Fresh cassava leaves
• Distilled water
• Ethanol (small amount)
• Mortar and pestle or blender
• Filter paper
• Test tubes
• Dropper
• Acidic and basic solutions for testing

Procedure

1. Collect fresh cassava leaves and wash them thoroughly with distilled water.
2. Chop the leaves into small pieces.
3. Grind the leaves using a mortar and pestle, adding small amounts of water to facilitate grinding.
4. Add a small volume of ethanol to improve extraction of the pigments.
5. Filter the mixture using filter paper to obtain a clear extract.
6. Test the extract with acidic and basic solutions and record the colour changes.

Many other local materials can be used:

• Red cabbage: Crush leaves, extract with water. Turns pink in acid, green in base.
• Beetroot: Cut into pieces, boil in water, cool and use the liquid. Colours change similarly.
• Turmeric: Powder the dried root, mix with water or ethanol. Turns red in basic solution, yellow in acid.
• Coloured flower petals: Rose, hibiscus, roselia flowers work well.

After preparing your indicator, test it with substances you can find at home or school:

A student in Arusha prepared an indicator from hibiscus flowers. She tested it with five different substances and recorded these results:

• Substance A: Red cabbage juice → turned pink
• Substance B: Lemon juice → turned pink
• Substance C: Soap solution → turned green
• Substance D: Pure water → remained purple
• Substance E: Ammonia solution → turned green

Question: Which substances are acidic and which are basic?

Answer:

• Acidic substances: A (red cabbage juice), B (lemon juice) - these turned pink
• Basic substances: C (soap solution), E (ammonia solution) - these turned green
• Neutral substance: D (pure water) - remained purple

This shows that the indicator successfully identified acids from bases.

• Always use clean equipment to get accurate results
• Fresh flowers and leaves give better results than old ones
• The indicator should be stored in a dark bottle if not used immediately
• Compare your results with synthetic indicators like litmus paper to verify accuracy

In everyday life in Tanzania, knowing how to make and use natural acid-base indicators can help you test the quality of food and household substances. For example, a farmer in Morogoro can test whether their soil is too acidic for growing crops by using an indicator made from red cabbage or cassava leaves — if the extract turns pink when mixed with soil water, the soil is acidic and needs liming. This simple method helps farmers decide how much agricultural lime (calcium oxide) to add to their fields to improve crop yields without needing expensive laboratory equipment.