Mass of round bottom flask (RBF): 52 Observed melting point of crude caffeine: (
ID: 959883 • Letter: M
Question
Mass of round bottom flask (RBF): 52 Observed melting point of crude caffeine: (Pure mp range is 235-236X) Mass of RBF + caffeine: Mass of extracted caffeine: Discuss the melting point range you determined from the crude caffeine. (I.e. Does this range seem appropriate? Why/why not?) Which technique (that we've already covered) would cause the melting point range to be more similar to the standard? How could you be certain that this technique works? Explain your choice and how you would do this in the lab. (Full procedure not necessary; just go deeper than listing one technique.)Explanation / Answer
The observed melting point for the crude caffeine is 230-232 oC, which is slightly lower compared to that of pure caffeine's melting point i.e. 235-236 oC. Here, the slightly lowered melting point of crude caffeine is due to the presence of other impurities (like tannic acid). Crude caffeine can be crystallized from a very small quantity of hot acetone or water to get pure crystalline silky needles of caffeine. Thus, crystallization technique would cause the melting point range to be more similar to the standard.