A student prepared solution of (i) an acid and (ii) a base in two separate beakers. She forgot to label the solution and litmus paper is not available in the laboratory. Since, both the solutions are colourless, how will she distinguish between the two?
In the absence of litmus, other natural or synthetic substances can be used to test acid and bases. Such substances are called indicators. Indicators such as methyl orange and phenolphthalein can be used to test the nature of a solution. These indicators show change in their colour in acidic, neutral and basic solutions. We can also use natural indicators such as turmeric and grape juice.
A few indicators with characteristic colour change are shown below.
S. No | Indicator | Colour in acidic solution | Colour in neutral solution | Colour in basic solution |
1. | Litmus | Red | Purple | Blue |
2. | Phenolphthalein | Colourless | Colourless | Pink |
3. | Methyl orange | Red/Pink | Orange | Yellow |
4. | Turmeric juice | Yellow | Yellow | Reddish brown |
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