PURE compound has higher melting point than the literature?

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Discussion Overview

The discussion revolves around the factors affecting the melting point of a pure compound, particularly when the observed melting point deviates from literature values. Participants explore potential causes for lower, higher, or broader melting ranges, considering aspects such as impurities, measurement inaccuracies, and the purity of the sample.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant suggests that a melting point lower than the correct value could be due to impurities, a poor thermometer, or pressure variations.
  • Another participant notes that a higher melting point might result from large impurities with higher melting points or inaccuracies in measurement tools.
  • Broad melting ranges are attributed to similar factors as those causing lower or higher melting points.
  • A later reply introduces the idea that ultra-high purity samples may exhibit different properties compared to standard high purity samples, potentially explaining discrepancies with literature values.
  • A link to a resource on polymorphism is provided, possibly indicating that phase changes could also be relevant to the discussion.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the causes of melting point discrepancies, and the discussion remains unresolved with no consensus on specific factors.

Contextual Notes

Limitations include potential missing assumptions about sample purity, the influence of environmental conditions, and the dependency on the definitions of "pure" in the context of melting point measurements.

stanton
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What went wrong with the condition or the procedures if I got the melting point of a pure substance to be:
(a) lower than the correct mp
(b) higher than the correct mp
(c) broad in melting range

I guess there's something to do with the pressure and wrong calibration, but I don't know what exactly causes the melting point of a pure compound to be broader, higher, or lower than the literature.
 
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(a) lower than the correct mp
Could be any number of things, including impurities (of any kind) in the substance, poor thermometer, pressure etc
(b) higher than the correct mp
Generally this could be caused by large impurities of a substance with a higher melting point or an inaccurate thermometer or pressure again
(c) broad in melting range
Same as above
 
hi,
most tables of melting points (& other stuff) reflect normal environmental samples (of high purity) but ultra high pure samples can have different properties and i suspect that is your case here.

karl
 
It' http://en.wikipedia.org/wiki/Polymorphism_(materials_science)"
 
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