Question

You are given a pure unknown sample with mp of 118-120 Celsius, which is either mandelic acid (lit. mp = 118-120) or succinic anhydride, along with pure samples of mandelic acid and succinic anhydride. Explain how you could determine its identity by a simple mp experiment that involves a single mp measurement. I understand how to identify the sample, but it's the question that follows is what I need the answer to... Following the procedure above, a student collects 6.0 g of product. What is his percent yield? Show calculations for the determination of the limiting reagent, the theoretical yield in grams, and the percent yield.

Answer 1

Melting point is a chractaristic physical property of any organic solid compound. To know the unknown, you can simply take small amount of unknown sample and throughly mix it with mandelic acid. make a uniform podwer of a mixture and then take the melting point of a mixture. If given unknown is a mandelic acid then the mixture should give uniform (or undeviated) melting range of 118-120^oC. But if the melting range is different then you can conclude that the given compound is succinic anhydride.

Concept behind this experiment: If the unknown is different from the given standard then both solids will melt at different melting temperature and hence your melting range will be different than standard compound's melting range. And if unknown is same as the standard in the mixture the both compounds will melt within same melting range. Hence we can say that unkown is the standard compound taken in the mixture.