Chemical Indicator

WHAT IS AN INDICATOR?

A chemical indicator is a substance that undergoes a distinct observable change when conditions in its solution change. This could be a color change, precipitate formation, bubble formation, temperature change, or other measurable quality.

PHENOLPHTHALEIN

The formula of phenolphthalein is C20H14O4

WHAT IS IT ?

Phenolphthalein is an acid-base indicator which is colorless in acid solution, but turns colourless to pink as the solution becomes alkaline.

PROCEDURE

1ST  STEP

Aqueous solution of sodium carbonate, barium chloride and potassium dichromate(+HCl) is prepared with distilled water in three different beakers.

2 nd STEP

Adding the Phenolphthalein indicator to the aqueous solution of sodium carbonate makes it turn pink due to its basic nature.

3rd STEP

The mixture is then added to another beaker containing aqueous solution of barium chloride which makes the solution chalky white. 

4th  STEP

Again the whole solution has to be transferred to the last beaker containing aqueous solution of K2Cr2O7  + HCl resulting in a mixture which is yellow in color.

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Sr. Secondary School