How do you use solvent extraction for purification?

Solvent extraction is used for purification by separating compounds based on their relative solubilities in two different immiscible liquids.

Solvent extraction, also known as liquid-liquid extraction, is a method to separate compounds based on their relative solubilities in two different immiscible liquids, usually water and an organic solvent. It is an extraction of a substance from one liquid phase into another liquid phase. This technique is often used when the substance to be extracted is dissolved in an aqueous phase which is then contacted with an organic solvent.

The process begins by adding the two immiscible liquids into a separation funnel. The mixture to be separated is added to the funnel and shaken gently. The two liquids will form two distinct layers because they are immiscible. The denser liquid will sink to the bottom while the less dense liquid will float on top. The compound to be extracted will dissolve in the solvent in which it is more soluble.

After allowing the layers to separate, the bottom layer can be removed by opening the stopcock of the separation funnel. This process is known as 'running off'. The top layer can then be poured off into a different container.

The choice of solvent is crucial in this process. The solvent should be chosen such that it does not react with the compound to be extracted and it should be immiscible with the solvent that the compound is initially dissolved in.

This method is widely used in the purification of substances, especially in the production of fine organic compounds. It is also used in the extraction of metals and the preparation of pharmaceuticals. It's a simple, yet effective method for separating and purifying compounds.