in Organic lab we performed a recrystallization of an unknown compound. our weig
ID: 715469 • Letter: I
Question
in Organic lab we performed a recrystallization of an unknown compound.
our weight before recrystallization: 0.105 g
after recrystallization : 0.557g
the melting point before: 119.5 - 124.5 degrees C
melting point after: 119.7 - 122.5 degrees C
in our experiment we discovered we had benzoic acid by comparison of the after melting point to a chart of boiling points
which benzoic acid had the closest.
We have a worksheet in which we need to calculate the yield and explain if it is satisfactory or not. I assumed it was percent recovery but the math doesnt look right. It is the last box on tge sheet. Also I was unsure of what to put on the volume at the top, if you know and could tell me that would be great.
Explanation / Answer
Recrystallization
I think you are putting wrong numbers
before crystallization weight = 0.105 g
after crystallization weight = 0.557 g (this is incorrect)
It may be 0.0557 g after recrystallization (again check this value)
mass of recyrstallized product cannot be greater than the crude material.
This was also confirmed by smaller range of melting point after recyrstallization. The substance purity increases.
Percent yield thus becomes = mass of recyrstallized product x 100/0.105 g
= 0.0557 x 100/0.105 = 53.05%
The purity of the material after recrystallization is greater than the crude material, however, the melting point of the product obtained is still quite broad when compared to the reported melting point of benzoic acid. It still has impurity in it. We need to repeat the recyrstallization process again to get higher purity material.
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.