Question

What is the purpose of performing mixed melting point experiments? For example, if your unknown is phenacetin, what do you expect to see with a mixed melting point experiment using your unknown and phenacetin out of a bottle? What do you expect to see with a mixed melting point using your unknown and acetanilide out of a bottle?

Answer 1

Mixed melting point experiment is basically used for identifying the compound . As there can be compounds which can have experimentally or accidentally same melting point . So to get rid of these kind of situation mixed melting point experiment is used. As the melting point of the mixture is less than that of the pure compound. Then if a mixture of two compound is made with one unknown and one known and if the mixed melting point experiment give the same melting point as that of the known compound then it means that the unknown compound is actually the same compound hence it is not actually a mixture but the purecompound. But if the mixed melting point experiment give the melting point value less than that of the melting point of the known compound then it means that the unknown compound is actually different from the known compound. The same procedure can be followed with phenacetin .As if the unknown compound with phenacetin in the mixed melting point experiment give the melting point as that of phenacetin then the unknown compound is phenacetin otherwise not.Similarly when the unknown compound mixed with acetanilide and the mixed melting point experiment is performed then if it give the same melting point as that of acetanilide then it shows that it is not a mixture we have prepared but pure acetanilide hence the unknown compound is acetanilide. But if it give different melting point then we assure that the unknown compound is not acetanilide. Hence from the above disccusion we conclude that the mixed melting point experiment is used to ensure the puritu of the compound.