write a short note on natural indicators
Indicators are substances whose solutions change colour due to changes in pH. These are called acid-base indicators. They are usually weak acids or bases, but their conjugate base or acid forms have different colours due to differences in their absorption spectra.
Natural Indicator -- An indicator prepared from natural substances (from plants, insects etc) is known as natural indicator.
Example - Litmus, Turmeric, red cabbage, etc.
Litmus is a water-soluble dye extracted from certain lichens, turns red when it contacts something acidic and blue with alkaline materials. They are available as litmus papers.
Turmeric (curcumin) is a natural indicator used to differentiate between acidic and basic solutions. It turns from yellow at pH7.4 to red at pH8.6. Turmeric will turn pinky-red in alkali, but is yellowish in both acid and neutral solutions.
Cabbage (red) contains anthocyanins, is a natural indicator used to differentiate between acidic and basic solutions. The colour of red cabbage is enhanced with the addition of vinegar or other acid.
When cooked in aluminium pans, which cause amore alkaline environment, the colour changes to purple and blue.