Question

4) when using a drying agent (sodium sulfate for example) to dry an organic layer, how do you determine if your layer is dry?

5) you purified a solid by recrystallization. describe the specifics as to why you did this. why was water chosen as the recrystallizzation solvent. why did you skip hot filtration? di something not go as planned?

all crude samples were approximately 90% pure, which means that in an ideal world your recovery would be about 90%. your recovery will likely be lower than this. describe two of the most likely sources of lost product.

Answer 1

Q.4. Drying agent

• The drying agent is the hygroscopic substance also called as desiccant which absorbs moisture, inducing or sustaining state of dryness in its vicinity.
• Ideally they are chemically stable and inert.
• Used in laboratory to remove water traces in the organic solutions eg: sodium sulfate, calcium sulfate.
• Drying agent may change its physical appearance to confirm that the moisture is absorbed eg: CaSO4 is blue when dry and when absorbs water it changes to pink.
• Sodium sulphate is used to remove water from the organic solutions. NaSO4 is added to the solution until the crystals no longer clump together. some times after getting dry the organic substance start flowing freely, this confirm that the organic layer is dry.

Q,5.

• Recrystallization is a technique used to purify the chemical substance by dissolving in the solvent along with the impurity. Usually water being universal solvent for polar compounds, is used in recrystallization.
• When substance is dissolved in excess of water, the associated impurity get soluble in water, removed and the required substance can be obtained by filtration method.
• For example in case of preparation of dulcin from phenetidine. Potassium cyanate reacts with acetic acid to give potassium acetate and Isocyanic acid. This Isocyanaic acid reacts with phenetidine to form Dulcin. But the potassium acetate remains as the impurity. To remove the same the Dublin is made through recrystallisation. By dissolving or washing with excess amount of water the potassium acetate is removed as soluble in water and Dulcin forms crystals which are collected by filteration and dried.

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