Theory:

The petals of china roses also act as a natural indicator. In this lesson we will do an experiment to know how that is work.
Note: Anthocyanin, a water-soluble pigment found in china roses, changes colour when it reacts with an acid or a base.
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Hibiscus flowers
Example:
How to prepare a China rose indicator?
 
Step 1:
Take some petals china roses in a cup.
 
Step 2: And some warm water in that cup.
 
Step 3:
Let it rest aside until the water colour changes.
 
Step 4:
Filter the solution.
 
Result: The filtered coloured solution will act as the indicator to test the acid and base solutions.
Note: China rose indicator changes the acidic solution to magenta (dark pink). It turns the basic solution to dark green colour and no colour change in neutral solutions.
Let us now test the below solutions for their acidity and basicity by adding the prepared solution to it. And observe the changes in their colour.
 
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Solutions to be tested
  
Solutions to test
Colour change
Acid/Base
Soap solution
Dark green colour
 Base
Lemon juice
Dark pink colour
Acid
Sugar solution
Dark pink colour
Acid
Vinegar
Dark pink colour
Acid
Tea, coffee, wine
Dark pink colour
Acid
Cold drinks
Dark pink color
Acid
Salt solution
Dark green color
Base
 
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Colour change in acids: Dark pink colour
 
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Colour change in base: Dark green colour.