Lab 1 - Orgo Lab #1 Melting Point Melting Point: one of the...

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Orgo Lab #1 – Melting Point Melting Point : one of the characteristic physical properties of a solid o used for : 1) to characterize a known compound (if you had to identify between several unknown compounds) 2) record a physical characteristc for a new compound 3) to establish purity of a known compound if an experiment reliably forms this known compound or if you are taking a melting point of a known compound o Impure compounds will melt over a wider range of temperatures and at a lower MP than original. Why? Energy is used to overcome crystal lattice energy to melt a solid. You need energy to break crystal lattice impurities disrupt crystal lattice, so requires less energy to break intermolecular forces o [*side note : Temperature range of 1-2 degrees is still pure—narrow ranges = ok! There will always be a range] Large melting ranges mistakenly make you think you have an impure sample. If sample is pure but still chunky, it will eventually end up in the pure melting point. Melting Point Apparatus o You will be using Mel-Temp melting point apparatus like fig. 3.10 (draw sketch for pre-lab) Filling Melting Point Capillaries 1) Sample must be dry Why? Because Moisture from solvents like water and other solvents will depress the MP’s (like an impurity) 2) Sample must be finely powdered Why? If sample is in chunks, sample will not pack well causing air pockets that slow heat transfer. Air pockets are not good heat conductors and sample will appear to have large melting range 3) Sample must be packed tightly How? By rapping sharply on a hard surface. Why? To avoid air pockets 4) Sample must not be more than 2-3mm high Why? If too much in capillary, there will be a differential in temp. throughout the sample (and if you have a differential there will be a range) o Steps 2-4 is to ensure efficient transfer of heat throughout sample
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Determination of Melting Point o Sample in capillary tube is placed in sample holder of Mel-Temp. Record range (not just 1 point). o Def of melting range : the temperature from when the first drop of liquid is observed to the temp when sample is completely liquefied (it’s observed what you see, not real melting range. *we record the observed) o Real melting range : from eutectic point to when sample is completely liquefied. shrinking, sogging, color change, texture changes, and sweating
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This note was uploaded on 03/07/2012 for the course 830 201 taught by Professor Leyton during the Fall '08 term at Rutgers.

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Lab 1 - Orgo Lab #1 Melting Point Melting Point: one of the...

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