filtrate
Summary
Filtrate is the liquid that passes through the filter during filtration, carrying the solvent and dissolved solutes; the solid left on the filter is the residue. Whether the product is in the filtrate depends on the step, as in hot filtration versus collecting crystals.
Detail
Meaning: Filtrate is the liquid that passes through the filter paper or frit during filtration. It holds the solvent and whatever is dissolved in it. The solid trapped on the filter is the residue (filter cake). Filtration separates by physical state, so it works when one component is insoluble in the solvent. In biology, filtrate also means the fluid forced from glomerular blood into Bowman's capsule.
On the MCAT: Passages describe a purification, often recrystallization, and ask where the product is. In hot gravity filtration, insoluble impurities stay on the paper and the dissolved product is in the filtrate. After cooling, the product crystallizes, and vacuum filtration keeps the crystals on the filter while the cold filtrate (mother liquor) holds soluble impurities and some product. Using too much solvent leaves more product in the filtrate and lowers the yield.
Common confusion: Students assume the filtrate is either the product or the waste. It depends on the step: the liquid is kept in hot filtration, and the solid is kept when collecting crystals. Do not confuse it with distillate (condensed vapor) or eluate (liquid leaving a chromatography column). Ask what physically passed through the filter.
Sources
- Organic Chemistry (Klein)
- Organic Chemistry (Wade)
- Introduction to Organic Laboratory Techniques (Pavia)
Written for the MCAT and checked before it was published. For study reference only. Spotted an error? Let us know.