Recrystallizing out of methanol

[scienceboy2000]

Hi, I am trying to recrystallize salt from methanol. I am having trouble. This is exactly what I did:

I dissolved a gram of salt into 20 ml of methanol (the bottle I have says methyl hydrate but I read online that it's the same thing as methanol). Then I made a hot water bath. I put a pyrex dish into a pot of boiling water. Using an eye dropper, I dropped a few drops into the pyrex beaker. I expected the methanol to evaporate almost immediately, leaving me with a thin flakey crystal that can easily be scraped off. But at best, I am left with a small piece of crust that is impossible to scrape off the pyrex dish. What is wrong?

 

[Borek]

No idea why you expected dried out substance to easily separate from the glass. It may, but it doesn't have to.

 

[Yanick]

What are you planning on getting out of this process? It seems to me that you are just spinning your wheels. Making a solution and evaporating the solvent leaves you with the material you started with minus some time and energy.

Recrystallizations are typically done to purify something from a mixture and requires either some background knowledge of the system (what your compound is, what impurities might be there etc) or a bunch of trial and error.

See Wikipedia for a intro discussion: Recrystallization

 

[scienceboy2000]

Thanks for the replies! I have read a lot about crystallization and I will be doing some experiments over the next couple of days. I will update this thread if I have any questions.

 

[LudusRex]

Hello,

Thank you for sharing your experiment with me. From what you have described, it seems that the issue may be with the temperature of your water bath. Methanol has a relatively low boiling point of 64.7°C, so it is possible that the water bath was not hot enough to fully evaporate the methanol. This could result in a thicker layer of salt crystals forming instead of the thin flakey crystal you were expecting.

I would recommend using a thermometer to ensure that the water bath is at the correct temperature before adding the drops of methanol. Additionally, you may want to try using a larger amount of methanol to dissolve the salt, as this can help with the evaporation process. It is also important to make sure that the pyrex dish is completely clean and free of any residue, as this can impact the formation of crystals.

I hope this helps and good luck with your experiment! If you continue to have trouble, I suggest consulting a lab manual or seeking guidance from a peer or instructor.