Question

Why extraction with small amounts of solvent rather once with largeamount?

Answer 1

Answer:

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 (see below). This phenomenon will often be observed if sodium bicarbonate is used for the extraction in order to neutralize or remove acidic compounds

Answer 2

Answer:

Because extraction is about maximizing surface area contact between the two solutions, and you simply get more surface area contact with smaller volumes. You can mix two smaller portion faster and more rhoroghly than large portions.