Q&A for How to Crystallize Organic Compounds

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Why should warm pentane and ether solutions not be suction filtered?

Community Answer

Both are highly volatile and will boil into the aspirator or vacuum pump trap.

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Question

How do I start the crystallization of sugar?

Gideon James

Community Answer

It starts with two major events: nucleation and crystallization. Clarified sugar cane juice is boiled in evaporators, which leaves a thick syrup. The syrup is then boiled at low temperatures, the seeding is added, and the product is then put in a centrifuge to separate the crystalline sugar and molasses. The seeding is what is most important, since that produces the nuclei.

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Question

Which compound is the best for crystallization?

NSEasternShoreChemist

Community Answer

If you want to practice, benzoic acid. It's very soluble in boiling water and very insoluble in ice-cold water. It's also rather nontoxic and no flammable solvents are involved.

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What is an effective method for purification of volatile solids? What separation method can induce crystals to grow?

NSEasternShoreChemist

Community Answer

Sublimation will work well for volatile solids if you have a vacuum pump. If you can't get crystals to grow, try scratching the inside of your flask with a glass stirring rod. If that doesn't work, put the flask in a freezer/ice bath. If you can't get crystals, then you have too much solvent.

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What additional steps should be added in the crystallization of napthalene procedure to remove impurities insoluble in solvent?

NSEasternShoreChemist

Community Answer

Napthalene is best recrystallized from EtOH. Hot gravity filtration ought to work fine.

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Question

How do I remove color impurities and hazy appearance in the solution?

Community Answer

Using a dehydration agent will remove the haziness which is usually due to water. Sometimes the dehydration compound will also bind the colored impurities or you can use activated charcoal. Both charcoal and dehydrating agents are separated by filtration.

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What happens when crystals of cetanol are put in boiling water in a beaker?

NSEasternShoreChemist

Community Answer

Nothing. Cetanol is too nonpolar to dissolve in water to a significant extent, regardless of temperature. Try using a less polar-solvent; ethanol might be a good choice. If that doesn't work, try cyclohexane.

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How do I select the amount of solvent for saturating the impure solute?

NSEasternShoreChemist

Community Answer

Slowly add solvent until most of your solute has dissolved. If adding a little more of the suitable solvent has no effect on the amount of solid left, then you've added enough solvent and any remaining solvent is an insoluble impurity.

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