Question

A. The goal of any separation or purification step is to completely remove unwanted material (maximize purity) and recover all of the desired material (maximize yield or recovery). Unfortunately, you often sacrifice one to maximize the other, so it ’s always a balance between the two. a) Is there any point during the extraction or recrystallization that you could visually tell that you were losing benzoin? b) Is there any information on the TLC plates that indicated that benzoin was lost? c) What changes could you make to minimize the loss of benzoin? B. After running a reaction you are asked to extract the product into diethyl ether (3 x 5 mL). a) How do you do this? (give a detailed, step - wise procedure) Keller/Stickley/Vaughn Chem 2255 b) Why should you then wash your extract with water? c) If you can't see any water droplets, do you still have to dry the solution with sodium sulfate? Why or why not? d) You want to evaporate the solvent by leaving it in the back of the hood until the next lab period. Should you stopper the flask? Why or why not? e) Upon returning the next lab, you weigh your crude sample (1.538 g) and recrystallize with hot isopropa nol. How do you know how much isopropanol to add?

Answer 1

a) How do you do this? (give a detailed, step - wise procedure) Keller/Stickley/Vaughn Chem 2255

To extract the product in diethyl ether we use a separating funnel

Take all compound in water or other solvent which in immiscible with diethyl ether and add 5.00 ml diethyl ether.

Then shake it well.

When stalled   both layers ; separate then into two flask.

Repeat this method with reaming amount of diethyl ether .

b) Why should you then wash your extract with water?

If the compound extract with diethyl ether or organic solvent means it is   soluble in the organic solvent not in water.

When we wash the extract with water, then compound will not dissolve only impurities will dissolve.

c) If you can't see any water droplets, do you still have to dry the solution with sodium sulfate? Why or why not?

If we can't see any water droplets we still have to dry the solution with sodium sulfate because there are small amount of water may be present . thus to dry completely we need little amount of sodium sulphate.

d) You want to evaporate the solvent by leaving it in the back of the hood until the next lab period. Should you stopper the flask? Why or why not?

We should should stopper the flask because compound will evaporate or volatile also.

e) Upon returning the next lab, you weigh your crude sample (1.538 g) and recrystallize with hot isopropa nol. How do you know how much isopropanol to add?

In the minimum amount of hot isopropa nol; because excess amount of hot isopropa nol will not give crystal of the compound.