Extraction

Extraction is a technique to separate components from a mixture. You are already familiar with extraction. Any time you steep tea, you're extracting water-soluble compounds, like caffeine and flavors, from the tea leaves into your hot water. This is an example of a solid-liquid extraction.

Liquid-liquid extraction is another type of extraction where the mixture is dissolved in two immiscible liquid phases. The solvents must be immiscible, meaning they do not mix and are separate phases. Liquid-liquid extractions are performed in a separatory funnel so that the more dense solvent will settle to the bottom and the less dense solvent will sit on top. Then, each solute compound will transfer to the phase in which it is most soluble. Therefore, it is important to choose solvents with different polarities.

In general, non-polar solutes will partition into the organic phase, and polar solutes will partition into the aqueous phase. The partition coefficient, K, is the ratio of solute concentration in the organic phase to that in the aqueous phase. Once the solutes have separated, the two different phases are collected. Keep in mind that it is likely that there will be residue of each component in both phases.

An acid-base extraction is a special type of liquid-liquid extraction that separates acidic and basic compounds based on the solubility differences. Recall that an acid is a compound that donates a proton when dissolved in water, and a base is a compound that accepts a proton.

To separate acidic compounds, a base is added to the mixture. The base will accept a proton from the acidic compound, making it ionic. Conversely, adding an acid would transfer a proton to a basic compound. In both instances, the ionic compound will transfer to the aqueous phase, and the neutral compounds will partition to the organic phase. The ionic compound is collected and then either deprotonated or reprotonated to convert it back to its original compound.

In this lab, you will separate a mixture of cellulose, benzoic acid, and caffeine. First, you will use extraction and filtration to isolate cellulose. Then, you will perform an acid-base extraction to separate benzoic acid and caffeine.