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When recrystallization fails to occur at room temperature adding a seed crystal or scratching the side...

When recrystallization fails to occur at room temperature adding a seed crystal or scratching the side of the flask tends to cause crystals to form. Why would this happen?

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Answer #1

During recrystallization process, if crystals doesn't appear then scratching of walls of test tube is done and many times it works and crystals appear. Behind it, the reason is scratching discharge tiny glassy crystals which act as site of nucleation and crystals starts appearing.

If scratching is not working then seeding is done. In this, very tiny crystal of the compound is added and it again acts as site of nucleation and crystal growth happen around it.

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