[Mikez]

Hi,

I just finished a recrystallization exp. (get unknown, purify, check melt point) I have 2 quick Questions:

1. What can I do after I've completed the experiment to confirm that the substance was successfully purified?

2.Why is a mixture of 2 compounds melt over a broad temperature?

My Attempt

1. I would think that u just take the melting point? since there really isn't anything else you can do...(my substance is vanillin)

2. Well, my textbook shows a bunch of graphs of binary mixtures that make no sense to me at all....

Thanks for replies

[macman104]

That deals with the eutectic point.  For a molecular explanation, here's a quote from this site:
http://www.owlnet.rice.edu/~chem217/MeltingPt.html

Melting points can also be used to access purity. You are all familiar with the concept of freezing point depression. Impurities in the solution prevent the ordering necessary to form a crystal lattice. This is why salt/water solutions will not freeze until sometimes as low as -20 °C. The concepts involved with melting points are similar. In a perfect crystal with no impurities the melting point will occur at one temperature. However when impurities are introduced there is no longer a continuous crystal structure. Instead the solid is made up of different regions, some with more crystal imperfections then others. Not surprisingly the melting point will not be as sharp. This will also cause the melting point to begin earlier then expected.