Page 128 - Chemistry_Form_2

Chemistry
for Secondary Schools

4. Add about 20 cm of distilled water to the residue and stir to obtain an
3
indicator solution.
5. Establish the colour of an indicator prepared by testing it with hydrochloric
acid and sodium hydroxide, one at a time.
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Questions
1. How can the colour changes observed with hibiscus flower extract help
determine whether a substance is an acid or a base?
2. Why was ethanol used as a solvent in the extraction instead of water?
3. What other substances found in your environment can be used as acid-base
indicators?

Activity 5.5

Aim: To prepare a pH indicator from cassava leaves

Requirements: Fresh cassava leaves, distilled water, ethanol, mortar and pestle or
blender, filter paper, test tubes or small clear containers, dropper
or pipette, known acidic and basic solutions (for example,
vinegar, lemon juice, baking soda solution, soap solution), pH
paper or a pH meter

Procedure
1. Collect fresh cassava leaves and rinse them thoroughly with distilled water to
remove any dirt or impurities.
2. Chop the leaves into small pieces and then grind them thoroughly using a
mortar and pestle. Alternatively, use a blender to blend the leaves into a fine
pulp.
3. Add a small amount of distilled water to facilitate the grinding or blending
process.
4. Add a small volume of ethanol to the mixture to enhance the extraction of
pigments, especially anthocyanins.
5. Filter the homogenous mixture using filter paper to separate the liquid extract
from the solid leaf residues. Collect the filtrate in a clean beaker.

6. Establish the colour of an indicator prepared by testing it with the acidic and
basic solutions available, one at a time.

Student’s Book Form Two 121

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CHEMISTRY FORM TWO NEW 2025 DUMMY.indd 121