During liquid-liquid extraction, how are organic and aqueous layers typically separated?

The correct answer focuses on the principle of separating organic and aqueous layers, which is primarily based on their differences in density. During liquid-liquid extraction, two immiscible liquids—typically an organic solvent and an aqueous solution—are mixed. The organic layer, which is often less dense than water, will float on top of the aqueous layer. This density difference allows for a straightforward separation of the layers after they have been allowed to settle.

When the mixture is left to stand, the distinct densities lead to a clear separation. The denser aqueous phase will accumulate at the bottom while the lighter organic phase remains on top. This allows for easy decantation or careful siphoning of one layer from the other, typically using a separatory funnel. This technique is efficient and effective as it relies on the physical properties of the liquids involved rather than chemical reactions or additional processes.

In contrast, centrifugation involves spinning the mixture at high speeds to accelerate the separation of components based on their density but is not the primary method used in standard liquid-liquid extraction setups. Similarly, evaporation of solvents is a technique used for concentrating solutions or recovering solvents but does not apply to the separation of layers in an extraction. Stirring the solution vigorously can promote mixing rather than separation,