PURE compound has higher melting point than the literature?

[stanton]

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.

 

[Rebooter]

(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

 

[karl-karl]

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

 

[chemisttree]

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

 

[DeeNos]

As a scientist, it is important to critically analyze all aspects of an experiment and consider possible sources of error or discrepancies. In this case, if the melting point of a pure substance is found to be different from the literature, there are a few potential factors that could have gone wrong with the conditions or procedures.

(a) If the melting point is lower than the literature, it could be due to a few reasons. One possibility is that the substance was not pure enough, which can lower the melting point. This could be caused by contamination from another substance or impurities present in the sample. Another possibility is that the substance was not heated at a slow and steady rate, which can affect the accuracy of the melting point. Additionally, the calibration of the equipment used to measure the melting point could be off, leading to an incorrect reading.

(b) If the melting point is higher than the literature, it could also be due to a few factors. Similar to the previous scenario, the substance may not be pure enough or the equipment may not be properly calibrated. Additionally, the substance may have been heated too quickly, which can cause the melting point to be higher than expected. It is also important to consider the source of the literature and if the conditions used to determine the melting point were different from your own experiment.

(c) If the melting point has a broad range, rather than a specific temperature, it is likely that the substance is not pure. The presence of impurities or a mixture of substances can cause the melting point to be less defined. Other factors such as the rate of heating and calibration of equipment can also contribute to a broad melting range.

In conclusion, there are several factors that can affect the melting point of a pure substance and cause it to be different from the literature. It is important to carefully consider the experimental conditions and potential sources of error in order to accurately determine the melting point of a pure compound.