Im doing a conclusion on a lab of acetaminophen. We were to take a melting point of the crude smale of acetaminophen and melting point of the crystallized acetaminophen.

The mp for crude sample: 169.2 degree C
The mp for crystallized sample: 172. degree C

Why the change in mp's? Is it because the second mp was less pure?

There was also a difference in the % yields. The crystallized sample % yield was less than the crude sample, why?

IF ANYONE could help me answer this, I would greatly appreciate it!

Think this thing through!!
Remember from freshman chemistry about depression of melting point. To refresh your memory, perhaps you will recall that when a non-volatile solute (such as an impurity) was added to a non-volatile solvent (such as PURE acetominophen), the melting point of the pure sample was lowered. Isb't that what your data showed?

Wouldn't you EXPECT the yield to be lower for the pure sample as opposed to the impure sample. That's what recrystallization is all about. You want to place the crude sample in a solvent, somtimes at a slightly elevated temperature, let the solution cool, and let the PURE crystals recrystallize, leaving the IMPURITIES behind in the solvent. You get less PURE material because the impurities have been left behind.

The change in the melting points of the crude and crystallized samples of acetaminophen can be explained by the presence of impurities. When impurities are present in a substance, they can disrupt the regular crystal lattice structure and lower the melting point compared to the pure substance.

In the case of acetaminophen, the crude sample had a melting point of 169.2 degrees Celsius, while the crystallized sample had a slightly higher melting point of 172.0 degrees Celsius. This suggests that the crystallized sample was purer than the crude sample.

During the process of recrystallization, the crude sample is dissolved in a solvent and then cooled to allow the pure acetaminophen to crystallize. The impurities, which may have different solubilities in the solvent, are left behind in the solution. This selective dissolution and recrystallization process helps remove impurities, resulting in a purer sample.

The lower percentage yield of the crystallized sample compared to the crude sample is expected because the impurities are left behind during the recrystallization process. The yield is a measure of the amount of pure acetaminophen recovered, so a purer sample will naturally have a lower yield since impurities are excluded.

In summary, the change in melting points and the lower percentage yield of the crystallized sample are both indicative of the successful removal of impurities through the recrystallization process.