Recrystallization Percent Recovery

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In summary, the conversation discusses calculating the percent recovery of an unknown solid and questioning if it represents the true value of the recovered pure solid. It also raises the question of how to determine the improvement in quality of an unknown solid after recrystallization. The concept of "true value" is explained as being the actual yield of the pure component in the sample, rather than just the percentage of the recrystallized material in the original sample. The conversation concludes by mentioning the need for testing methods to determine the purity of the recrystallized material.
  • #1
SciFiGuy2012
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Homework Statement


Calculating percent recovery of an unknown solid and describing if the percent recovery represents the "true" value of the recovered pure solid.

How do we know that quality of an unknown solid which was recrystallized improved as a result of the recrystallization?

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For the first question, I am confused because I don't understand what the "true value" means. I got 75% as my percent recovery, but I don't understand what the question means by "true" value.

For the second question I have no idea what it's saying. After recrystallization we expect the compound to be purer. But we have to give some "evidence". So please help me there.

Please help.

Thanks.
 
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  • #2
SciFiGuy2012 said:

Homework Statement


Calculating percent recovery of an unknown solid and describing if the percent recovery represents the "true" value of the recovered pure solid.

How do we know that quality of an unknown solid which was recrystallized improved as a result of the recrystallization?
You have to test it some way. What types of tests are you familiar with that deal with purity?

For the first question, I am confused because I don't understand what the "true value" means. I got 75% as my percent recovery, but I don't understand what the question means by "true" value.

It means just what it implies. If you recover a solid from a fairly pure sample, the yield you get and the true recovery are one and the same. If the sample is heavily contaminated with something else, what you obtain might be all there is of the component that you recrystallize. In this case the true yield might be very good even though the percent recovery only reflects the (much lower?) concentration of the recrystallized material in the original sample.
 
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The percent recovery in recrystallization is a measure of the amount of pure solid that was successfully recovered from the impure sample. It is calculated by dividing the mass of the recovered pure solid by the initial mass of the impure sample and multiplying by 100%. This value does not necessarily represent the "true" value of the recovered solid, as it is possible for some impurities to remain in the final product. However, a higher percent recovery generally indicates a more successful recrystallization process.

As for the second question, there are a few ways to determine if the quality of the unknown solid has improved as a result of recrystallization. One way is to perform a melting point determination before and after recrystallization. If the melting point of the final product is higher and more narrow, it is an indication that the recrystallization process was successful in purifying the solid. Another way is to perform a qualitative analysis, such as a TLC or HPLC, to compare the impurities present in the initial sample to those in the final product. If the impurities are significantly reduced or eliminated, it is further evidence of the improved quality of the solid after recrystallization.
 

FAQ: Recrystallization Percent Recovery

What is recrystallization percent recovery?

Recrystallization percent recovery is a method used in chemistry to determine the efficiency of a recrystallization process. It measures the amount of desired product that is recovered after a purification process.

Why is recrystallization percent recovery important?

Recrystallization percent recovery is important because it indicates the effectiveness of a purification process. A high percent recovery means that a higher percentage of the desired product was obtained, indicating a successful purification process.

How is recrystallization percent recovery calculated?

Recrystallization percent recovery is calculated by dividing the mass of the purified product obtained by the initial mass of impure product, and multiplying by 100. The formula is: % recovery = (mass of purified product / initial mass of impure product) x 100.

What factors can affect recrystallization percent recovery?

The purity of the initial sample, the effectiveness of the solvent used, the temperature and rate of cooling, and the presence of impurities can all affect the recrystallization percent recovery. The technique and skill of the chemist performing the recrystallization process can also play a role.

How can recrystallization percent recovery be improved?

To improve recrystallization percent recovery, it is important to use a high purity starting material and an appropriate solvent. Adequate cooling and filtration techniques should also be employed. If the percent recovery is consistently low, it may be necessary to revisit the purification process and make adjustments to improve the efficiency.

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