Indicators and their Uses

Lesson Plan of Indicators and their Uses

General Science Grade VIII

Students’ Learning Outcomes

·         Define indicators.
·         Use indicators to identify acids, alkali and neutral substances.
·         Investigate the color changes in the extracts of various flowers and vegetables by adding acids and alkali.

Information for Teachers

·         An indicator is a chemical compound that can change its color when an acid or an alkali is added into it.
·         A chemical detector for protons in acid-base tit rations.
·         Artificial indicators are the made-made indicators such as universal indicator phenomenological & methyl orange. 

Concept Map

·         Litmus can only tell you about the acidic or alkaline nature but a universal indicator like pH paper can tell you the strength of acids and alkali.
·         Natural indicators are present naturally and we have to extract these from natural sources such as, rose, periwinkle, red spinach and red cabbage.
·         Different indicators give diff100 ml water- filter if necessary. Rent colors in different media “Making Methyl orange indicator” add 0.1 gm. methyl orange in 100 ml water-filter if necessary.

Material / Resources

Tubes, test tube, methyl orange, phenomenological, dropper, red cabbage, steel pot, transparent bottles

Worm up activity

·         Write the word “indicators” on board & ask students to give their ideas about it. Write students’ ideas on the board.


Activity 1

·         Place three transparent liquids in three beakers labeled as A, B and C on the table.
·         now, ask students:
     Q1: Can you guess; which is an acid, which contains an alkali and which one is water?
              (Expected response: Don’t taste)
·         after getting their responses divide students in groups and instruct them to:
o   Take a small amount of solutions, separately in three test tubes.
o   Take a blue litmus paper.
o   Dip the litmus paper in the above solutions separately and note the change n color.

·         Make your own Litmus paper.
1.       Chop the red cabbage with a sharp knife.
2.       Crush it with pestle and mortar.
3.       add a small amount of water
4.       Pour the blue liquid in a beaker and soak some blotting / filter paper into it.
·         Tell the students that test tube ‘A’ contains an acidic solution, test tube ‘B’ contains an alkaline solution and ‘C’, contains a neutral solution.
·         Repeat the experiment by using pH (l C) indicators.
·         Add indicators with a dropper.
·         Explain children that pH paper turns red I acidic, dark green in basic and light green in neutral solution.
·         Explain children that phenomenological cannot be used to distinguish  between an acidic and neutral solution as it becomes colorless in both.
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·          Conclude all l1, l b and 1c activities y telling students that test tube ‘A’ contains acidic, test tube ‘B’ contains alkaline while test tube ‘C’ contains neutral solutions.

Activity 2

·         Ask the students to copy it in their notebooks.
·         Draw the following table on board and discuss it. (Whole class discussion)
Color change when placed in different solutions
Blue Litmus
Red Litmus
Rose Extract
pH Paper
Blue/ Dark Green
Light Green
Color less
Red Cabbage
Methyl Orange
(Sada Bahar)
Red spinach extract

                                       Sum up / Conclusion

·         Conclude Lesson by telling students that they learns about.
o   Indicators are the substances used to check the acidic and basic nature of solution.
o   Indicators can be natural (i.e. extracted from plants) or artificial (Extracted from chemical compounds)
o   PH paper is a universal indicator which can measure strength of acids and bases.


·         A group of high school students are on their way to the forest Changa Manga (name of forest) on a research expedition. Their task is to study the quality of water & soil. Unfortunately, the bag containing the indicators was not brought. Instead of going back and wasting time, they decide to carry on their study by using natural indicators. As their research teacher, what plants would you suggest to the students and why? Briefly explain how students will prepare the plant extracts and then test various soil & water types.

Follow up

·         Ask students to check pH of water from hand pump or wells located near an industry / tannery. Suggest its possible effects on environment.
·         Students can be asked to find pH of soil of nearby field and suggest what kind of fertilizers should be used to neutralize soil’s acidity/basically.



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