Question

are all of the acid-base indicators pure substance? that is, does the solution contain a single species? justify your answer, using specific examples.

Answer 1

The acid base indicators are not a single species in solution

Acid base indicators are generally represented by the formula HIn and they partly dissociate into H+ and I- ions

HIn <--------> H+ + I-

K = [ H+ ] [ I- ]/[ HIn ]

According to Le chatlier principle, the equillibrium is shift to forward or backward depends on the H+ ions.

In acidic solutions ( more H+ ) the equillibrium shift to the left and more Hl is formed

In basic solutions ( more OH- ) H+ ions removed by OH- and the equillibrium shift to right and more I- is formed

Example

Phenolpthalein is weak acid with dissociation into H+ and In-

HIn (undissociated form ) is colorless

In- (dissociated form ) is pink colur

In acidic solution HIn is dominated and the solution is colourless

In basic solution In- is dominated and the solution is pink colour