INDICATOR – WORKING FOR PHENOPHTHALINE – WORKING FOR METHYL ORANGE

by • 27/08/2013 • GeneralComments (0)230

INDICATOR:

DEFINITION

Indicators are weak organic acid or weak organic base which indicate the end point of an acid base titration by the help of a particular color.

 

EXAMPLE

Weak organic acid (Phenolphthalein)

Weak organic base (Methyl Orange)

 

WORKING FOR PHENOPHTHALINE

Consider the example of phenolphthalein which is a weak organic acid. A fix amount of acid is present in the conical flask with phenolphthalein. In the addition of base form burette, reaction between acid and base occurs to form salt and water so that the quantity of acid decreases in the conical flask continuously.

When all amount of acid is finished the base added in the conical flask react with phenolphthalein to produce pink color which shows that acid base titration reached to its end point that is

InOH + HCL ————-> H2O + CL- + In- color

WORKING FOR METHYL ORANGE

Consider the example of methyl orange which is weak organic base. A fix amount of base is present in the conical flask with methyl orange. In the addition of acid form burette, reaction between acid and base takes place to form salt and water so that the quantity of base decreases in the conical flask continuously. When all amount of base is finished the acid added in the conical flask react with methyl orange to produce reddish pink color which shows that acid and base titration reached to its end point that is

InOH + HCI ————-> H2O + CL- + In- color

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