Filter (chemistry)

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diagram of a simple filtration. where the filter blocks some substance but allows another one to cross

In chemistry and common usage, a filter is a device (usually a membrane or layer) that is designed to block certain objects or substances while letting others through. Filters are often used to remove harmful substances from air or water, for example to remove air pollution, to make water drinkable, to prepare coffee. In domestic food and drink preparation where bulk solids are removed from liquids, this is often called a strainer.

Filtrate is the liquid produced after filtering a suspension of a solid in a liquid. Filtrand (or Residue) is the solid residue remaining in the filter following filtration^{[citation needed]}.

For certain situations, such as separating an aqueous substance from a solid one, filtering may be replaced with decanting.