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

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SUMMARY

The presence of impurities in substances leads to a depression of their melting points, a phenomenon that can be quantitatively analyzed using a depression curve. Specifically, the melting point of pure aspirin is 135°C, and the extent of melting point depression can indicate the level of impurities present. The concept of eutectic mixtures is crucial, as these mixtures exhibit the maximum melting point depression. Understanding the chemical nature of the compounds involved is essential for accurate analysis.

PREREQUISITES
  • Basic knowledge of melting point concepts
  • Understanding of eutectic mixtures in chemistry
  • Familiarity with the principles of freezing point depression
  • Experience with chemical analysis techniques
NEXT STEPS
  • Research the properties and applications of eutectic mixtures in chemistry
  • Study the principles of freezing point depression and its relationship to melting point depression
  • Explore analytical techniques for measuring melting points, such as differential scanning calorimetry (DSC)
  • Investigate the effects of various impurities on the melting points of different substances
USEFUL FOR

Chemists, materials scientists, and students studying physical chemistry who are interested in the effects of impurities on melting points and the analysis of phase diagrams.

Monroe
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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.
 
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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.
 

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