Anonymous asked in Science & MathematicsChemistry · 7 months ago

Melting point determines the identity of the unknown compound. Why “mixed melting point” method is used?

also why IR spectroscopy is a better method to determine an unknown?

2 Answers

  • 7 months ago
    Favorite Answer

    There are a large number of compounds that have coincidentally identical melting points. Therefore, caution should be used in identifying a compound based solely on matching the literature melting point. However, mixed melting points offer an ability to almost certainly identify an unknown compound.

    Grind roughly equal portions of the unknown and known samples together to mix well and take a melting point of the mixture.

    If the two substances are identical the melting point should be the same as that of either sample.

    If the two substances are not identical, then the melting point will be depressed.

    IR gives a lot more information about the compound .The presence of certain functional groups like carbonyl and alcohol is the main advantage of IR but alone it cannot identify an unknown. Mass Spec and NMR are need to do that .

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  • Mike A
    Lv 7
    7 months ago

    The two are complementary. Infrared will give more structural information particularly on what functional groups are present but it will not tell you if you have a mixture. A melting point will tell you little about the identity of a material but if it melts over a range of several degrees C it is a good indication that the material is impure.

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