Introduction
Substances such as lemon, oranges juice and vinegar tastes sour. These is because they substances contains acids. The chemical nature of these substances is acidic. The acids in them are natural.
Some substances taste bitter with their solutions filling soapy when rubbed between the fingers when touching. These are bases. Their chemical nature is basic.
Plant extracts as acid-base indicators.
To determine if a substance is acidic or basic we use indicators.
Indicators change colour when added to a solution contain either a n acidic or basic substance.
Turmeric, litmus among others are some of the naturally occurring indicators.
Cautions:
Do not taste anything unless the teacher asks you to do so.
So not touch anything unless the teacher asks you to do so.
Preparing and using Plant Extract indicators.
Requirements.
Red cabbage.
A mixer or blender.
Water.
Filter paper.
Common solutions such as lemon, milk, vinegar and bleach.
Procedure.
Cop some red cabbage and put it in a mixer or blender.
Add water to it.
Mix until juice is formed.
Strain(filter) this mixture in to a beaker. This is the natural indicator.
Use the prepared red cabbage indicator to test whether the household solutions are acidic or basic.
What observations did you make?
What can you conclude from your observations?
Observation and explanation.
Acidic substances change colour of the solution from purple to red or pink.
Neutral substances turn the purple solution to blue.
Basic substances change the colour of the purple solution to green or yellow.
Therefore, red cabbage is a natural indicator.
Categories of different household solutions.
Indicators are substances that change colour when added to acidic or basic solutions.
Common indicators used in the laboratory are:
Litmus paper.
Phenolphthalein.
Methyl orange
Litmus indicator solution turns red in acidic solutions, blue in basic solution and purple in neutral solutions.
Colour changes of litmus paper indicators in different solutions.
| Red litmus paper | Blue litmus paper. |
Acidic solution | Stays red | Turns red |
Neutral solution | Stays red | Stays blue |
Basic solution | Turns blue | Stays blue |
The table below shows colour of Methyl Orange and Phenolphthalein in acidic, neutral and basic solutions
Indicator | Acidic solution | Neutral solution | Basic solution |
Methyl Orange | Red | Yellow | Yellow |
Phenolphthalein | Colourless. | Colourless | Pink |
Indicator | Acidic solution | Neutral solution | Basic solution |
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