There are two main types of indicators you need to know:

1. Natural Indicators – These are extracted from plants and vegetables found in Tanzania. Common natural indicators include:

• Red cabbage juice (changes from pink/red in acids to green/yellow in bases)
• Hibiscus flower extract (red in acids, greenish-yellow in bases)
• Cassava leaf extract
• Turmeric
• Litmus (extracted from lichens)

2. Synthetic Indicators – These are manufactured in laboratories. Common synthetic indicators include:

• Phenolphthalein (POP): Colourless in acids, pink in bases
• Methyl Orange (MO): Red in acids, yellow in bases
• Litmus paper: Blue litmus turns red in acids; red litmus turns blue in bases

The pH scale measures how acidic or basic a substance is, ranging from 0 to 14:

• pH 0–6: Acidic (lower pH = stronger acid)
• pH 7: Neutral (like pure water)
• pH 8–14: Basic/alkaline (higher pH = stronger base)

What You Need

• Prepared indicator (e.g., hibiscus extract or litmus solution)
• Phenolphthalein and methyl orange (if available)
• Test tubes or small containers
• Dropper
• Test substances from your locality, such as:
  • Lemon juice or citrus fruit juice
  • Tomato juice
  • Sour milk
  • Vinegar
  • Soft drink
  • Wood ash solution (for base)
  • Soap solution

Procedure

1. Prepare your test substances: If using solid substances like wood ash or soap, mix a small amount with water and let it settle. Use the clear liquid (supernatant) for testing.

2. Label your containers: Each test substance should be in a separate, labeled container.

3. Add the indicator: Using a clean dropper, add 2–3 drops of your prepared indicator to each test substance.

4. Observe and record: Note the colour change that occurs in each container.

5. Repeat with other indicators: If available, test the same substances with phenolphthalein and methyl orange to confirm your results.

Example Test Results

If you test lemon juice (acid) and soap solution (base) using different indicators, you should observe:

• If the indicator changes to the acid colour, the substance is acidic.
• If the indicator changes to the base colour, the substance is basic.
• If there is no colour change, the substance is neutral.

For example, when you add phenolphthalein to vinegar, it remains colourless because vinegar is acidic. When you add the same indicator to soap solution, it turns pink because soap is basic.

A student in Arusha collected the following substances from home: lemon juice, tomato juice, milk, and soap solution. She tested each using phenolphthalein indicator and recorded her observations:

• Lemon juice: Colourless (acidic)
• Tomato juice: Colourless (acidic)
• Milk: Colourless (neutral or slightly acidic)
• Soap solution: Pink (basic)

From these results, she concluded that lemon juice and tomato juice are acidic, while the soap solution is basic. The milk showed no colour change, indicating it is close to neutral.

In Tanzania, many household substances can be tested for acidity or alkalinity:

• Vinegar (acetic acid) – acidic
• Lemon juice (citric acid) – acidic
• Sour milk (lactic acid) – acidic
• Wood ash solution – basic (contains potassium carbonate)
• Soap solution – basic (contains sodium hydroxide or potassium hydroxide)

This knowledge helps in quality control, farming (testing soil pH), and everyday decision-making.

A small-scale tomato farmer in Morogoro can use a simple indicator (like red cabbage juice or litmus) to test the acidity of fermented milk (mtindi) before using it as a natural fertilizer. If the milk is too acidic, it may harm the soil plants; knowing this helps the farmer decide whether to neutralize it with wood ash (which is basic) before applying it to their tomato garden, ultimately protecting their crops and improving harvest yield.