Question

The dichloromethane was collected and then more dichloromethane was added to the tea water in the glassware.

Why is it better to add small amounts of the dichlormethane multiple times instead of just one large volume of dichloromethane?

1.Why perform mutlipole extrantions instead of just one?

2. Suppose you wanted to separate butylamine from hexane. Should the aqueous solution be acidic or basic?

3. Suppose you wanted to separate benzoic acid from hexane. Should the aqueous solution be acidic or basic?

Answer 1

Hardly ever all of the solute will be extracted since there is finite distribution coefficient for the compound. As a general rule, multiple extractions with small quantities of solvent or solution are more efficient than one extraction using the same amount of solvent .The amount of material left behind after two or three extractions is usually very small (less than 5 % in most cases) and does not justify the effort and resources (solvent and time to perform the extractions and to remove the solvent later on). Excessive washing will also lower the yield of the product, if the desired compound dissolves noticeably in the other phase.
Multiple extractions with smaller amounts of solvent are more efficient than a single extraction with the same total amount of solvent.