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02 - MP Recryst - CHEM 3221 Organic Chemistry I Pre-lab...

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LABORATORY EXPERIMENT 2 Melting Point and Recrystallization CHEM 3221 Organic Chemistry I Pre-lab Lecture UH DEPARTMENT OF CHEMISTRY
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CHEM 3221 Organic Chemistry I Pre-lab Lecture UH DEPARTMENT OF CHEMISTRY Melting Point Melting Point : The temperature at which, the solid is in equilibrium with its liquid phase. Melting Point Range : The span of temperature from the point at which the crystals first begin to liquefy to the point at which the entire sample is liquid. Pure compounds typically melt over a narrow temperature range of 1-2° C. Presence of soluble impurities almost always decreases and broadens the melting point range . Part A. Melting Point Determination Review of Terms
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CHEM 3221 Organic Chemistry I Pre-lab Lecture UH DEPARTMENT OF CHEMISTRY Melting Point Melting Point of a Mixture (X and Y) Eutectic Temperature : The lowest possible melting point for a mixture of 2 compounds. Eutectic Composition: The composition (ratio) at which both solid X and solid Y are in equilibrium with the mixture (at the eutectic temperature). EUTECTIC POINT
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CHEM 3221 Organic Chemistry I Pre-lab Lecture UH DEPARTMENT OF CHEMISTRY Melting Point Sample Preparation for MP Pack the capillary tube by pressing the open end gently into a sample of the compound to be analyzed. (Capillary tubes break easily!) The solid should fill the tube to a depth of ~2 mm. Tap the bottom of the capillary on a hard surface so that the crystals pack down into the bottom of the tube.
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CHEM 3221 Organic Chemistry I Pre-lab Lecture UH DEPARTMENT OF CHEMISTRY Melting Point The Melting Point Apparatus 1. Load the sample on the capillary tube, no more than 2 mm in height or just enough to be visible. 2. Place the capillary tube on the heating element slots and turn the heat on. DO NOT PRESS the ORANGE calibrate button. 3. Heat at a rate of 10° C/min until 10-15° C below the expected MP range then reduce the rate to 1°C/ min. 4. Record the temperature at which the crystals first begin to liquefy and the temperature where all of the sample is converted to liquid . This is your MP range. 5. Allow the apparatus to cool down naturally after each measurement. 75.1° C TEMPERATURE CONTROLLER HEATING ELEMENT EYEPIECE CAPILLARY TUBE SAMPLE FOR MP
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CHEM 3221 Organic Chemistry I Pre-lab Lecture UH DEPARTMENT OF CHEMISTRY Melting Point Experimental Notes Part 1. Take the melting point of BENZOIC ACID for practice (MP = 122-123° C).
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