Any compound can be classified based on its chemical properties
On the basis of their chemical properties, all the compounds can be classified into threegroups :
An indicator is used to detect the chemical properties of that compound
Turmeric is also a natural indicator
The red cabbage extract (obtained from red cabbage leaves) is also a natural indicator
The red cabbage extract remains red in acidic solutions but turns green on adding to basic solutions
The flowers of Hydrangea plant are usually blue which turn pink in the presence of a base.
The three most common indicators to test for acids and bases are : Litmus, Methyl orange and Phenolphthalein
Litmus Paper – Litmus is a natural indicator (whose neutral colour is purple).
Litmus is a natural indicator
Litmus Is obtained from Lichen a plant from thallophyte
An acid turns blue litmus to red.
A base (or alkali) turns red litmus to blue
The neutral colour of methyl orange is ‘orange’
Methyl orange indicator gives red colour in acid solution.
Methyl orange indicator gives yellow colour in basic solution
The neutral colour of phenolphthalein is ‘colourless’.
Phenolphthalein indicator is colourless in acid solution.
Phenolphthalein indicator gives pink colour in basic solution
Those substances whose smell (or odour) changes in acidic or basic solutions are called olfactory indicators
Exampls – Onion , vanilla, Clove
Onion ,Vanilla Loose its smell when it is added to a base like NaOH ,And does not loose its smell when added to a acid like HCL
You have been provided with three test-tubes. One of them contains distilled water and the other two contain an acidic solution and a basic solution, respectively. If you are given only red litmus paper, how will you identify the contents of each test-tube ?
Acid : An acid is a substance which dissociates (or ionises) on dissolving in water to produce hydrogen ions [H+(aq) ions
Acids Do Not Show Acidic Behaviour in the Absence of Water