An unknown sample was crystallized from benzene. on cooling to 0 degree centigrade in an ice bath the amount of crystals in flask was quite large, but much of it seemed to disappear when an attempt was made to collect it by suction filtration. Explain?
Since benzene has low melting point of 6 degrees , on cooling the soln to 0°c crystals formed since it was lower than m.p of benzene then on atempt of filtration the temp raised aproaching the mp of benzene hence crystals disappear again.
During suction filtration the crystals prepared from benzene disappeared due, the high speed and pressureof the vacuum filter to absorb the smallest particles of a crystals and the high vapour of a benzene cause a crystal to evaporate when was in a vacuum filter.
My guess it had a high vapor pressure as a solid (like moth balls) and sublimed under suction.
Well, it seems like those crystals are quite the elusive little things! They must have had a serious case of stage fright when you tried to collect them through suction filtration. Perhaps they saw the filtration apparatus and mistook it for the red carpet at the Crystal Oscars. They simply couldn't resist the urge to make a grand exit, disappearing into thin air and leaving you with a perplexed expression. But hey, don't worry, it happens to the best of us. Crystal celebrities can be quite fickle. Maybe next time you should try a more casual approach, like inviting them to a pool party. Who knows, they might feel more comfortable and actually show up!
The phenomenon you are describing is called "solvent loss" or "solvent evaporation" during suction filtration. This often occurs when the solvent used for crystallization (in this case, benzene) has a relatively low boiling point and is volatilized under reduced pressure.
Here's an explanation of why this happens during suction filtration:
1. Low boiling point: Benzene has a boiling point of around 80 degrees Celsius, which is relatively low compared to other solvents commonly used in crystallization. When the crystallization is cooled to 0 degrees Celsius in an ice bath, the temperature is well below the boiling point of benzene.
2. Reduced pressure: During suction filtration, a vacuum is applied to the filtration apparatus to speed up the filtration process. This reduced pressure lowers the boiling point of the solvent even further, causing it to evaporate more readily.
So, when you performed suction filtration on the crystallized sample, the reduced pressure caused by the vacuum likely caused the benzene solvent to evaporate, resulting in its loss. This is why, despite initially observing a large amount of crystals in the flask, much of it seemed to disappear during filtration.
To prevent or minimize solvent loss during suction filtration, you can take the following steps:
1. Avoid excessive vacuum: Use a moderate vacuum, rather than applying a strong vacuum, to minimize the pressure drop and reduce the boiling point of the solvent.
2. Decrease filtration time: Reduce the time spent under vacuum to minimize exposure to reduced pressure.
3. Use a higher boiling point solvent: If possible, consider using a solvent with a higher boiling point to crystallize your sample. This will reduce the likelihood of solvent loss during filtration.
By understanding the principles behind solvent evaporation during suction filtration and taking appropriate precautions, you can improve the collection and recovery of crystalline samples.