MP Lab PP - MeltingPoint&RefractiveIndex...

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he Theory and use of Melting Point and  Refractive Index to erify or Identify Organic Compounds Study Materials Slayden – pp. 17-22 Pavia – Tech 2; 3.9, 24 – Tech #9  (9.1 – 9.5; 9.7 – 9.9) Dr. Schornick Web Site  10/28/10 1
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lements of the Experiment Pre-lab report Melting Point Theory and Background Uses Melting Point Range Melting Point Ranges of Known Compounds, Mixtures,  Unknown Refractive Index Theory and Background Temperature Correction Refractive Index, with temperature correction for a  10/28/10 2
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Melting Point Melting Point Temperature at which a transition occurs between solid  and liquid phases Temperature at which an equilibrium exists between the  well-ordered crystalline state and the more random  liquid state Melting Point Range The  Onset point  (lower temperature) is the temperature  at which the liquid phase first appears in coexistence  with the crystals The  Meniscus point  is when a solid phase is at the  bottom and a liquid phase on top with a well defined  meniscus – Used as “Pelting Point” in Europe The  Clear point  is when the substance becomes  completely liquid – Used as “Melting Point” in USA 10/28/10 3
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Melting Point Uses Identify Compounds Establish Purity of Compounds Melting Point Depression Pure compounds display  little , if any, “melting point”  range, i.e., they have “ sharp ” melting points Mixtures of substances, i.e., the contamination of one  compound by another, whose components are insoluble  in each other in the liquid phase, display both a  melting  point depression  and, instead of a sharp melting point, a  melting point range The size of the melting point depression depends on the  composition of the mixture Generally, a 1% impurity results in a 0.5 C depression 10/28/10 4
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Melting Point Melting Point Indicates Purity in Two Ways The Purer the Compound, the Higher the Melting Point The Purer the Compound, the Narrower the Melting Point Range Melting point of A decreases as impurity B is added Eutectic Point is the Solubility Limit of B in A; Thus, it is the Lowest  Melting Point of an A/B mixture (Note: Sharp melting point, i.e., no range, at eutectic point) 10/28/10 5 Solid + Liquid Liquid A + B Solid A + B Range Clear Point Onset Point mp A mp B 0% B 0% A Temperature Eutectic Point mpB > mpA { MP Range
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Melting Point The Experiment Determine the melting point range of:
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This note was uploaded on 10/27/2010 for the course CHEM 223 taught by Professor Hardin during the Fall '10 term at CUNY Hunter.

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MP Lab PP - MeltingPoint&RefractiveIndex...

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