Filter (chemistry)

Filter (chemistry)

In chemistry and common usage, a filter is a device (usually a membrane or layer) that is designed to physically block certain objects or substances while letting others through, depending on their size. Filters are often used to remove solid substances suspended in fluids, for example to remove air pollution, to make water drinkable, and to prepare coffee. Some devices that are called filters may also carry out other processes, such as waste treatment, (e.g. biofilter). Several types of filters are used in chemistry in order to facilitate separation, thereby purifying a liquid (or gas). Many filters use gravity, or gravity enhanced by vacuum (suction) in order to create this separation, often through a funnel-shaped device. Filter efficiency can be improved in a number of ways, such as with the use of fluted filter paper. Other types of materials may be used to effect separations based on size, similar to filters, such as molecular sieves.

The process of passing a mixture through a filter is called filtration. The liquid produced after filtering a suspension of a solid in a liquid is called filtrate, while the solid remaining in the filter is called retentate, residue, or filtrand.