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)"