Melting point lab

Essay by num1qutieCollege, UndergraduateA-, February 2007

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Melting Points and Re-crystallizing


The purpose of this experiment is to select a suitable recrystallizing solvent, to be able to purify and separate acetanilide from a mixture by process of recrystallization. Organic compounds that are synthesized in labs or isolated from natural recourses often have been tainted by impurities. Recrystallization is a process that removes these impurities from solid organic compounds that are at room temperature. This process is built on the principle that the solubility of a compound increases with temperature and decreases as it cools down, into its crystal form.

We will also identify an unknown compound by mixture melting point.

Reagent Table:

Molecular weight g/molMp o CBP o CDensitySolubility

Acetanilide135.1652114.33041.219Less than.1g at 22oC

Trans-cinnamic148.161133300.9957-10 g per 100ml


Benzoic acid122.12122.42491.335Water

Toluic acid136.1111-1132631.05





Benzoic acid;

Toluic Acid:


Place 2 grams of impure acetanilide in a 125 mL Erlenmeyer flask. Add 30mL of water and one or two boiling chips and bring the suspension to a boil by heating it on a Hot plate.

Stir the system frequently with a glass rod. As soon as boiling begins add more water drop until all the solid dissolves. When all the acetanilide dissolves, remove the flask from the hot plate if the crystals easily deposit from solution as it cools, add 3Ml of water. Now slowly add a dash of activated charcoal. Place the flask on the hot plate again and the systems to a second boil.

Remove the hot solution from the hot plate and allow it to cool slightly. To the hot solution, add gradually and with considerable care so as to avoid excessive foaming, 0.25 to 0.50 g of decolorizing carbon pellets. With swirling or good stirring, bring the solution to a gentle boil for 1 - 3 minutes to remove small...