======Buchner Filtration======


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**Alternative titles:** Rapid Filtration of Crystals
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====Summary====                   
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====Procedure====  
  -Assemble apparatus: retort stand and clamp, side-arm vacuum flask, rubber adapter, Buchner funnel, vacuum source (e.g. water aspirator), and appropriate filter paper.
  -Check glassware for cracks; seat the funnel firmly in the adapter; clamp the flask securely; connect vacuum tubing to a trap and then to the vacuum source.
  -Choose filter paper that covers all funnel holes; moisten it with a small volume of the filtrate solvent so it seals flat against the plate.
  -Start gentle vacuum; pour the well-stirred slurry into the funnel in portions, keeping the liquid level below the rim to avoid bypass.
  -Rinse the original vessel with a small amount of cold solvent and pour over the cake to transfer remaining solids.
  -Allow the cake to compact; wash the cake with minimal cold solvent to remove impurities while limiting product loss.
  -Draw air through the cake for several minutes to pre-dry the solid; if needed, press gently with a spatula wrapped in filter paper to improve drainage.
  -Break the vacuum by opening to air before turning off the pump; remove the funnel; lift the paper and transfer the solid to a drying surface or oven.




====Links==== 
Buchner Funnel Filtration Technical Guide - Chemical Thinking Laboratory: {{youtube>ZwER7qEuRow?}}\\

Buchner Funnel - University of Bath: 
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====Variations====
  *Use a fritted glass funnel instead of paper when compatible with the solvent and product.
  *Precool the solvent and funnel when filtering cold crystallization mixtures to reduce product dissolution.
  *Add a thin diatomaceous earth bed for very fine particulates to prevent paper clogging.



====Safety Precautions====
  *Wear safety glasses, lab coat, and appropriate gloves; work in a fume hood if solvents are volatile.
  *Inspect and clamp the vacuum flask; avoid using chipped or cracked glass to reduce implosion risk.
  *Always break vacuum before shutting off the pump to prevent backflow and splashback.
  *Use a vacuum trap between the flask and the pump to protect the pump from solvent ingress.
  *Do not overfill the funnel; keep liquid below the rim to prevent spills and bypassing the paper.
  *Verify solvent compatibility with filter paper or frit; avoid hot solvents that can soften adapters.
  *Dispose of filtrates and washings following chemical waste guidelines.




====Questions to Consider====
  *Why wet the filter paper before pouring the slurry? (To seal the paper to the plate and prevent solids from slipping underneath.)
  *Why use cold solvent for washing crystals? (To minimize product dissolution while removing impurities.)
  *Why break the vacuum before turning off the pump? (To prevent backflow of liquid into the apparatus and sudden splashing.)
  *How do you choose filter pore size or paper grade? (Match to particle size; finer grades retain small particles but slow the flow.)
  *What does channeling in the cake do to purity and yield? (It allows liquid to bypass parts of the cake, reducing washing efficiency and potentially trapping impurities.)