1. You isolated the following compounds in lab and observed the melting points i
ID: 715872 • Letter: 1
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1. You isolated the following compounds in lab and observed the melting points in the table below judge the purity of cach compound. compound observed mp literature value for mp aphthalene benzophenone 45-470 48.1 -anisic acid salicylic acid acetate 1350 79-80 80.5° 178-182 184 135° 3-chlorobenzoic acid 157-158° 158 sulfanilamide 165-166 165-6 ferrocenc 157.5-161.5 172.5 2. You think that you have isolated ibuprofen in the lab. Since you don't totally trust your own laboratory techniques, you want to prove to yourself that you have ibuprofen before you ingest it. Using only melting point techniques, explain how you can prove that you actually have ibuprofen. (Assume the stockroom is able to supply you with any compound you need.) 3. The melting point of a pure compound is known to be 110-111o. Describe the melting behavior expected if this compound is contaminated with 5% of an impurityExplanation / Answer
Melting point is a characteristic physical property of a substance.It is useful in identification of a chemical substance.Closer the observed melting point to the literature melting point,higher the purity of compound.A pure crystalline compound usually have a sharp melting point and it melts completely over a narrow range of temperature of not more than 0.5 - 1 .
1) Ferrocene has soluble impurities present which has lowered its melting point.ferrocene is not pure.
Salicylic acid acetate, 3-chlorobenzoic acid and sulfanilamide are pure compounds as they are showing no deviations in their melting points.
Naphthalene and benzophenone shows 0.5-1 lowering from their melting points and instead of sharp melting point,are showing a narrow range of melting point,indicating that very little impurities are present.
P-anisic acid has soluble impurities present because it shows lowering of melting point and its melting range of temperature is 4.
2)The literature melting point of ibuprofen is 76.The student can first note the melting point of pure ibuprofen from stockroom and can then compare the melting point of the compound he/she prepared.If observed melting point of the compound prepared is same as ibuprofen's melting point,this will prove that prepared compound is actually ibuprofen .
3)If the compound is contaminated with 5% impurity,its melting point will get lowered and the range of melting point temperature will get increased from 1 .
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