Recrystallization of benzoic acid

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In summary, recrystallization is a technique used to purify solid compounds, such as benzoic acid, by dissolving the compound in a solvent and allowing it to slowly cool and form crystals. The most commonly used solvent for this process is hot water, but other solvents such as ethanol, methanol, and acetone can also be used. Recrystallization is considered complete when the solution has cooled and the crystals have formed, and a melting point test can be performed to confirm the purity of the compound. The same solvent can be used multiple times, but it may become less effective as it becomes contaminated with impurities. Factors that can affect the success of recrystallization include the choice of solvent
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fruitl00p
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Hello,

I did a lab on the recrystallization of benzoic acid. My solvent was hot water and used charcoal to adsorb any color impurities. I am trying to figure out how I should write a reaction and a mechanism for this. Is there even a reaction and mechanism I can write for this?

Any suggestions?
 
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  • #2
fruitl00p said:
... I am trying to figure out how I should write a reaction and a mechanism for this. Is there even a reaction and mechanism I can write for this?

No. Nope. Nyet. Nein...
 
  • #3


I can provide some guidance on how to approach writing a reaction and mechanism for the recrystallization of benzoic acid. Firstly, it's important to understand the purpose of recrystallization in this context - it is a purification technique used to remove impurities from a solid compound, in this case benzoic acid. The solvent, hot water, is chosen based on its ability to dissolve the compound at high temperatures, while also being able to precipitate it out at lower temperatures. The charcoal is used as an adsorbent to remove any colored impurities that may be present in the benzoic acid.

In terms of writing a reaction, it would be more accurate to describe the process as a physical change rather than a chemical reaction. The benzoic acid is simply being dissolved in the hot water and then recrystallized as the solution cools. However, there is a change in the physical state of the compound as it goes from a solid to a liquid and then back to a solid again. So, you could write a reaction that shows the dissolution of benzoic acid in hot water and its subsequent recrystallization upon cooling.

As for a mechanism, there isn't a specific chemical reaction occurring during recrystallization. Instead, it is a process that involves solubility and crystallization. You can describe the mechanism as follows:

1. The hot water dissolves the benzoic acid due to its high temperature and the polar nature of both the solvent and the compound.
2. As the solution cools, the solubility of the benzoic acid decreases, causing it to precipitate out of the solution and form crystals.
3. The addition of charcoal helps to adsorb any colored impurities, resulting in a purer product.
4. The crystals can then be collected through filtration and dried, resulting in a purified sample of benzoic acid.

I hope this helps guide you in writing a reaction and mechanism for the recrystallization of benzoic acid. Keep in mind that this is a physical process and not a chemical reaction, so the focus should be on the changes in physical state and solubility rather than specific chemical reactions.
 

FAQ: Recrystallization of benzoic acid

What is recrystallization and why is it used to purify benzoic acid?

Recrystallization is a technique used to purify solid compounds, such as benzoic acid. It involves dissolving the compound in a solvent and then allowing it to slowly cool and form crystals, which are then separated from the impurities in the solution. This process is used because it is able to remove impurities more effectively than other purification methods, resulting in a higher purity of the compound.

What solvent is typically used for recrystallization of benzoic acid?

The most commonly used solvent for recrystallization of benzoic acid is hot water. This is because benzoic acid is highly soluble in hot water, but less soluble in cold water. Other solvents that can be used include ethanol, methanol, and acetone.

How do you know when recrystallization of benzoic acid is complete?

Recrystallization is considered complete when the solution has cooled and the crystals have formed. Additionally, the solution should be clear, meaning that all impurities have been removed. To ensure the purity of the compound, one can perform a melting point test to confirm that the melting point of the crystals matches the known melting point of pure benzoic acid.

Can the same solvent be used for recrystallization multiple times?

Yes, the same solvent can be used for recrystallization multiple times. However, as the solvent is reused, it may become contaminated with impurities and less effective in purifying the compound. It is important to filter the solution after each recrystallization to remove any impurities that may have been introduced during the process.

What are some factors that can affect the success of recrystallization of benzoic acid?

Some factors that can affect the success of recrystallization of benzoic acid include the choice of solvent, temperature of the solvent, and the rate of cooling. It is important to choose a solvent in which benzoic acid is highly soluble at high temperatures, but less soluble at lower temperatures. The rate of cooling should also be slow to allow for the formation of large, pure crystals. Additionally, the use of a hot filtration can help remove any impurities that may hinder the recrystallization process.

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