Question

Students often notice that the pale pink phenolphthalein color disappeared from his or her titrated samples after a few minutes. explain why does this happen with the a chemical equation?

Answer 1

Ans- the pink color of phenolphthalein during an acid-base titration, it was due to the CO2 in the air making the solution acidic. A check with a pH meter quickly dispelled that notion. The color disappeared when the pH was 9 or 10 and even greater.

There are three forms of the phenolphthalein molecule. One in acid solution where the solution is colorless. Then there is a second shape to the molecule that occurs in basic solution that is the familiar pink color. And there is yet a third form that is colorless in basic solution. The rate of change between the first two is essentially instantaneous, but transition from second to third is slow which accounts for the gradual fading of the pink color.