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Answer the following questions:-1. Turmeric is(a) an acid (b) a base (c) salt (d) an indicator2. What are indicators? Name two olfactory indicators.3. Name two other natural indicators. How do they behave with acids and bases?
1. Turmeric is an indicator. [Option-(d)]
2. Indicators are substances that change colour when they are added to acidic or alkaline solutions. Litmus, phenolphthalein, and methyl orange are all indicators that are commonly used in the laboratory.
Olfactory Indicators: Substances which change their smell when mixed with acid or base are known as olfactory indicators. For example onion, vanilla, clove, etc. Onion: Paste or juice of onion loses its smell when added with base. It does not change its smell with acid.
3. Natural indicators -The indicators that are obtained from plants are known as natural indicators. A few examples of natural indicators are turmeric, china rosa, red cabbage and grape juice.
i. Red cabbage indicator- is useful as a pH indicator because their leaves contain a pigment molecule from the family of anthocyanins, known as Flavins, which are responsible for many of the red/purple/blue colours observed in fruits and vegetables.
In neutral solutions, the colour observed is purple. As the solution becomes more acidic a red colour results. Increasing the pH in basic solutions changes the colour from blue to green and at high pH, the solution is observed as greenish-yellow.
ii. Grape juice indicator- Purple grape juice changes its colour depending on the pH of the solution. An acidic solution like Vinegar turns grape juice pink/red. An alkaline solution like Baking Soda turns grape juice dark green.
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