CHEM 3112 Lecture Notes - Lecture 1: Eutectic System, Sample Size Determination
Document Summary
Qualitative technique used to determine purity and identify a compound. Identity is not definitively determined by a simple melting point. Impure organic compounds not only exhibit broad but also depressed melting points. Presence of impurities lowers and broadens the melting point. Eutectic point is the exact composition at which a mixture has a sharp melting point. Is lower than the melting point of both pure substances. Darkening that occurs at or below the melting point. Different crystalline forms are observed depending on the condition of crystallization resulting in more than one possible melting point. Water-containing molecules will have different melting points from the anhydrous forms of the same compound. Hundreds of different compounds will have melting points in the same range. Unknown samples must be mixed with suspected known compounds. Unknown + b = 130. 0-(cid:1005)3(cid:1005). (cid:1004) c pure or (cid:373)ixture of two ide(cid:374)tical co(cid:373)pou(cid:374)ds. Thermometers are initially calibrated when produced and marked with graduations varying degrees of precision.
