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Safari File Edit View History Bookmarks Window Help R 45% D Wed 6:40 PM a mycourses.purdue.edu https:/mycourses.purdue.edubbcswebdav/pid-10227135-dt-content-r. https://mycourses.purdue.edu/b bdav/pid-10421185-dt-conten... Chegg Study Guided Solutions and Study Help | Chegg.com DISCUSSION QUESTIONS 1. Summarize how you chose a solvent to use for the recrystallization of the unknown compound. Based on your experimental results, describe whether or not this particular recrystallization solvent was a good choice for the unknown compound. How did you use your experimentally determined melting point to identify your unknown solid? Describe what the melting point range for the unknown compound tells you about its purity. Were you able to conclusively identify your unknown? 2. Based on your experimental results, summarize the effectiveness of recrystallization to purify the unknown compound. That is, do you have any experimental evidence that indicates that the recrystallized unknown compound is still impure? 3. 4 What was the percent recovery for the recrystallization of your unknown;, was it high or low? Explain what might have caused the high/low percent recovery.Explanation / Answer
1).
Here are a few ways which will help yu the most suitable solvent for recrytallization :
a) The coumpound should be sparingly soluble at room temeprature but once heated to high temperatures, on flame or water bath, should be totally soluble.
NOTE : The compound shouldnt be totally soluble at room temeprature, because then the collection of recrystallised compound would be very difficult.
b) The solvent should vapourise after the crystallised compound has been obtained, so that the weight of the solvent doesn't add to the yield of the crystallised product.
c) The solvent shouldn't react with the product that is meant to be crystallised. The entire motive of recrystallisation would be rendered usless.
2)
Melting points can be used in the following way to help identify a compound:
If a sharp-melting point is obtained, then the query substance B is expected to the substance (say A) with the similar melting point. If according to chemical literature, the melting point of A is significantly different from the one calculated experimentally of B, then B doesnt have the same structure as A.
If the compound has an impurity present then the melting point would be lower than a literature value with a much broader melting range as compared to a sharp one in case of a pure compound.
3) If the weight of the recrystallized compound is more or less than the theoretical yield, which can be due to incomplete evaporation of solvent, wrong way of purifying the compound, then the recrystallization can be ineffective.
4)
Low yield will occur when :
- Too much solvent is added, that recovery of recrysttalised compound becomes so difficult
- the solid is dissolved below the boiling point of the solution.
High yield will occur when :
-The recrystallised sample is not dried enough, that the weight of the solvent is still present in the coumpound.
- Impurities are still present because recrystallization wasn't carried out properly.
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