In the preparation of a soluble salt using titration, using sulphuric acid and sodium hydroxide and phenolphthalein as indicator, why would the salt crystals formed be pink and how do you get rid...

In the preparation of a soluble salt using titration, using sulphuric acid and sodium hydroxide and phenolphthalein as indicator, why would the salt crystals formed be pink and how do you get rid of the pink color?

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ncchemist | eNotes Employee

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The acid base reaction you are talking about is below.

H2SO4 + 2NaOH --> Na2SO4 + 2H2O

The sulfuric acid and sodium hydroxide form sodium sulfate and water.  Sodium sulfate is the soluble ionic salt formed.  A small amount of phenolphthalein is added as the titration indicator.  When the titration reaches the equivalence point (equal number of moles of acid and base present), the phenolphthalein turns from colorless to pink in color.  The color change is the visual indication of the equivalence point.  That is why the salt crystals are pink colored.  You can get rid of this pink color by washing the salt crystals in an organic solvent like ethanol.  The sodium sulfate will not be soluble in ethanol but the phenolphthalein will be.  You will have colorless crystals left behind.

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