Filtration is a separation technique used to separate the components of a mixture containing an undissolved solid in a liquid. The exact method used depends on the purpose of the filtration, whether it is for the isolation of a solid from a mixture or removal of impurities from a mixture.
The principle of filtration is based on the difference in sizes between the particles. Filtration separates the solid matter from a liquid mixture using a filter medium, for example, filter paper or filtration membrane, that allows the liquid to pass through it and block the solid particles on the other side of it. The pores of the filter medium are bigger compared to the solvent particles but are smaller compared to the solute particles, so they allow only solvent particles to pass through them, leaving the solute particles on the other side, making the solution free from the insoluble solute. The mechanism of "filtration" can be mechanical, biological, or physical. Filtration may be done cold or hot, using gravity or applying vacuum, using a Buchner or Hirsch funnel or a simple glass funnel.
As the process of filtration uses the concept of difference in the particles, we have two types of mixtures:
A homogeneous mixture of two or more components is called a solution. A solution has two components:
Various types of processes are used for filtration. In general, the filtration process uses the filtration membrane that allows only a specific size particle to move through it, making the solution at one end free from the insoluble solute particles. Insoluble solid substances left behind are called residues. We can understand this by using the example of filtering sand and water, where a muslin cloth at the mouth of the container containing the sand and water allows only water to pass through, separating the sand from the sand and water solution. Filtration paper can also be used in place of muslin cloth as the filtration membrane.
Filter paper is a semi-permeable barrier placed perpendicular to a liquid or air flow. Filter paper can have pore sizes ranging from small to large to permit slow to fast filtering.
Vacuum filtration uses a Buchner funnel. A Buchner funnel is a flat-bottomed, porous, circular porcelain bowl with a short stem. The stem is fitted with a rubber stopper and inserted into the mouth of a side-arm filter flask. Circular filter paper, the same diameter as the bowl, is placed on the flat bottom and wetted with the appropriate solvent to create a seal before starting the filtration.
When making coffee, hot water is filtered through the ground coffee, and the coffee bean. The filtrate is the coffee in liquid form. Using a tea ball or a tea bag (paper filter) for tea is also an example of filtration.