Recrystallizing out of methanol

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In summary, the individual is attempting to recrystallize salt from methanol but is encountering difficulties. They have added a gram of salt to 20 ml of methanol and placed a pyrex dish in a hot water bath, but the resulting substance is not easily separated from the glass. The purpose of this process is unclear and it may require further experimentation or knowledge of the system to achieve success. The individual plans to continue experimenting and may ask for further assistance.
  • #1
scienceboy2000
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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?
 
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  • #2
No idea why you expected dried out substance to easily separate from the glass. It may, but it doesn't have to.
 
  • #3
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
 
  • #4
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.
 
  • #5


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.
 

1. What is the purpose of recrystallizing out of methanol?

The purpose of recrystallizing out of methanol is to purify a substance by dissolving it in a solvent (methanol), and then allowing it to slowly crystallize out, leaving behind impurities.

2. What type of substances can be recrystallized out of methanol?

Most organic compounds can be recrystallized out of methanol, including salts, acids, and bases. However, some substances may not dissolve well in methanol and may require a different solvent.

3. How does recrystallization out of methanol work?

In recrystallization, a sample of impure substance is dissolved in a hot solvent (methanol), and then allowed to cool slowly. As the solution cools, the solubility of the substance decreases, causing it to crystallize out, leaving behind impurities that remain dissolved in the solvent.

4. What is the importance of controlling the cooling rate in recrystallization out of methanol?

The cooling rate is important in recrystallization as it affects the size and purity of the crystals formed. A slow cooling rate allows for larger, purer crystals to form, while a fast cooling rate may result in smaller, less pure crystals or no crystals at all.

5. Can the same solvent be used for multiple recrystallizations?

Yes, the same solvent can be used for multiple recrystallizations as long as it is still able to dissolve the substance being purified. However, over time, the solvent may become contaminated with impurities, and a fresh batch of solvent may be needed for optimal results.

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