General questions 1. What aspects about a compound can be established from its m
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General questions 1. What aspects about a compound can be established from its melting point? 2. How is melting behavior affected by the use of too much sample? 3. What is the likely consequence of allowing a reflux to proceed too vigorously? 4. Give the three most important attributes of an ideal solid-liquid extraction solvent. 5. In the context of recrystallization what consequence(s) is(are) associated with rapid crystal growth? 6. What are the four principle categories of weak intermolecular interactions, ranked from strongest to weakest? Strongest Second strongest Third strongest WeakestExplanation / Answer
1) The melting point of a compound is a physical property that can be used to characterize or identify the compound. Usually, melting points of almost all common chemicals used in lab are available in databases; a comparison of the melting point of an unknown compound with listed compounds in databases can be used to identify the compound.
The melting point of the compound can be an indication of its purity. A pre compound usually melts over a narrow temperature range of say 1-2°C. An impure compound melts over a much broader range, say 5-10°C. Thus, noting the melting point of an unknown compound can help us determine if the compound is pure.
For compounds (mostly organic compounds) belonging to the same class (say alcohol family, works only for small molecules, upto 10 or 12 carbon atoms), a higher melting point indicates higher intermolecular forces and hence, the higher the molecular weight.
2) The melting point is an intrinsic property, i.e, the melting point is independent of the weight of the compound taken. However, taking too much compound in the capillary (in case of determination of melting point by sulfuric acid bath) may obscure the correct determination of the melting point. Too much solid may make it difficult to observe when the solid starts to melt and affect melting point determination.
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