When a reaction has finished, the desired product should be present in the reaction flask. However, there are likely to be many other things also present – solvents, unreacted starting materials, by‑products etc. In order to isolate the product with a reasonable level of purity, these other things must be removed, and the general procedures for isolating different types of product are called “work-up”. General procedures for work-up can vary enormously, depending on the nature of the product. For example, if the product crystallises from the reaction mixture, the work-up may simply consist of filtering the mixture to recover the solid product, and then recrystallising the product. If the product is a liquid, it may be possible to purify it conveniently by distillation. However, in many cases, the reaction mixture will consist of a mixture of organic and aqueous material, and the work-up will involve more steps, such as extraction and washes with various solutions. These operations are often called “aqueous work-up”, and are detailed in this section.