A student suspected that an unknown was undergoing a chemicalchange at its melti
ID: 683640 • Letter: A
Question
A student suspected that an unknown was undergoing a chemicalchange at its melting point. Suggest a simple method for testingthe hypothesis. Why does a soluble impurity reduce the melting-point range ofa pure compound ? why is it advisable to run a mixed melting-point determinationon samples of two different compositions before concluding that thetwo compounds are identical ? any help would be appreciated, thnx! A student suspected that an unknown was undergoing a chemicalchange at its melting point. Suggest a simple method for testingthe hypothesis. Why does a soluble impurity reduce the melting-point range ofa pure compound ? why is it advisable to run a mixed melting-point determinationon samples of two different compositions before concluding that thetwo compounds are identical ? any help would be appreciated, thnx!Explanation / Answer
A student suspected that an unknown was undergoing a chemicalchange at its melting point. Suggest a simple method for testingthe hypothesis.Take an IR or NMR of both the product before and aftermelting. if no chmeical reaction occurred they should be thesame. If a chemical reaction occurred they should bedifferent. why is it advisable to run a mixed melting-point determinationon samples of two different compositions before concluding that thetwo compounds are identical ? if you run a mixed melting point you should see both partsmelts at the exact same time if they are the same. With amixed melting point you do not have to worry about the accuracy andprecision of your instruments such as a thermometer. Why does a soluble impurity reduce the melting-point range ofa pure compound ? a soluble impurity will have a lower melting point than aninsoulbe impurity, because if something is soluble it dioes notrequire excess heat tro melt it. so if you 25% impurity and75% pure your melting point will decrease by about the perecentagetimes its melting point.
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