The pale pink color of the titration solution at the end point will fade to colorless...

The pale pink color of the titration solution at the end point will fade to colorless after several minutes when exposed to the atmosphere. Account for this color change.

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Expert Solution

1) The above mentioned observation seems to be happen during acid - base titration wherein a phenolphthalene indicator is being used to monitor end point.

2) Phenolphthalene indicator shows fait pink colour in slightly basic medium (this slightly basic medium neccesarily formed after slight excess addition of a base like NaOH beyound end point.

3) Further it's observed that this pale pink coloured solution when exposed to an environment for several minute fade to colourless. This reason for this can be the dissolution of CO2 which creates slighltly acidic envirnment following belowe equation,

CO₂ + H₂O -------------> H₂CO₃ <--------> H⁺ (aq.) + HCO₃^- (aq.)

These protons (H+) will neutralize excess HO- ions and makes sloution neutral as that of at end point of titration.

And in neutral medium phenolphthalene indicator will not exhibit any colour and hence solution fade to colourless.

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queen_honey_blossom answered 1 year ago

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