Narration : 14. Hot Filtration & Recrystallization
- Crystalline compounds containing a small amount of impurities can be purified by hot filtration followed by recrystallization.
- Add a specific amount of distilled water to the sample. The sample is not completely dissolved at this time.
- Heat the sample on the electric heater. Also, heat distilled water in a separated beaker.
- Stir the mixture and add a minimum amount of the heated distilled water to completely dissolve the sample.
- If an excess amount of distilled water is added, the desired amount of crystals may not be obtained.
- Add the heated distilled water 2 or 3 times through the Büchner funnel with the filter paper into a beaker in the filtration chamber. Discard the heated water in the receiving beaker.
- Immediately, filter the heated sample solution before the apparatuses cool down.
- In hot filtration, the impurity less soluble than the sample will remain on the filter paper.
- Allowing the filtrate to slowly cool down to room temperature gives the crystals of a high quality.
- Don't apply a shock to the solution, as it will lower the quality of the crystals.
- Also, don't rapidly cool the solution.
- Using a new filter paper, collect the crystals thus obtained by suction.
- Soluble impurities remain in the solution and are removed by filtration.