How Does the Presence of Impurities Affect the Melting Point of Substances?

[Monroe]

I have tried a quick scan of the web for general information relating to the depression of melting points and found very little available, so i started this thread. The general idea is a depression curve which will help you identify by how much a sample contains impurities. I was looking for data on the depression of melting point of aspirin, which should have a melting point of 135. I would hazard a guess that the depression of freezing point is inversly the same thing. Any info would be appreciated.

 

[chemisttree]

The melting point depression is dependent on the chemical nature of the two or more compounds in the mixture. The mixture that gives you the maximum melting point depression is called the "eutectic" mixture... another search term for you.

There is some good data out there for some eutectic mixtures.

 

[quicknote]

Thank you for starting this discussion on the depression of melting points. I can provide some insight on this topic.

The depression of melting points, also known as the freezing point depression, is a phenomenon that occurs when impurities are present in a substance. This causes the melting point of the substance to decrease compared to its pure form. This is because the impurities disrupt the regular arrangement of particles in the substance, making it more difficult for them to overcome the intermolecular forces and melt.

In your search for data on the depression of melting point of aspirin, it is important to note that the amount and type of impurities present can vary, leading to different degrees of depression. Additionally, the depression curve you mentioned is a useful tool for determining the purity of a substance by comparing its melting point to the expected value for a pure substance.

As for the relationship between the depression of melting points and freezing points, they are indeed inversely related. This is because the freezing point is the temperature at which a substance transitions from liquid to solid, while the melting point is the temperature at which a substance transitions from solid to liquid. Therefore, any impurities that lower the melting point will also lower the freezing point.

I hope this information helps in your understanding of the depression of melting points. Further research and experimentation can provide more specific data on the depression of melting points for different substances.