[springgy]

I have a question which says discuss purity of your product from the melting point and then compare this to the literature value. I always thought that the higher the melting point becomes, the less pure the substance I have made is. But when I read on the internet, it says, the higher the melting point, the more pure the product is =/ I have a literature value of 212 degrees C, and I got 220 degrees for the substance I made. Does that mean what I have made isn't very pure, or is pure?

[Borek]

I would say you have made something else.

[agrobert]

I would run a TLC.  If you followed the literature for your reaction and you have only one major product I would say that your melting point apparatus is not calibrated (thus giving you a high mp).  Reported melting points often vary in literature so you should have another way to characterize your product.  So if it is pure by TLC then you should recrystallize your product and then run a mp.  In general melting point tells you how pure or dry a compound is by its range.  A narrow range would be  say 212-213 C and a wet or impure range could be completely off or melting over several degrees.  Give us more information.  You can calibrate your mp apparatus with a pure sample of benzoic acid.

[Arkcon]

Colligative properties apply not only to solutes, like common salt, in water but also to mixtures of solid compounds.  Therefore, an impurity, like 10% unreacted solid or competing product, in your synthesized compound will result in freezing (or melting) point depression.  So impure solids have lower melting points.

Of course, like Borek said, if it's 90% impurity and 10% desired product, then you might end up with a melting point far away from product, even though the melting point will still be low for that impurities published value.

[springgy]

Thanks for the feedback guys. I'm not exactly sure what has gone on then as my friend made the product. I just carried out the melting point on it. We will be running a NMR or IR on it soon, so at least that should tell me if it is what it should be, haha.

[springgy]

Actually, just looked at the value again, and it's 212-217, so 219-220 is alright, right? I, or my friend was making p-nitroacetanilide.

[Yggdrasil]

Oftentimes, overestimation of the melting point of the compound by a few degrees occur because of heating the compound too fast in the melting point apparatus.