Exam (elaborations)
Lab 2: OCHEM 1
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Lab 2: OCHEM 1 Melting point of a solid compound **** temperature at which a phase transition from solid to liquid occurs Melting point of a pure crystalline compound ****
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Lab 2: OCHEM 1Melting point of a solid compound **** temperature at which a phase transition from
solid to liquid occurs
Melting point of a pure crystalline compound **** temperature at which thermal energy
is sufficient to break down the crystal lattice of the solid
sharply defined
highly reproducible
Very precise melting points have been measured for a few compounds by determining
**** the temperature at which the pure liquid/solid are in equilibrium
Narrow or sharp melting points are evidence that the compound is **** pure
The presence of impurities affects mp by **** depressed relative to that of the pure
substance, and mp is off by a substantial amount.
We record the melting point when we see the **** first droplet
Based on the information in the Experiment PDF, what effect(s) may a residual solvent
or trace amounts of water have on the mp of a known compound? **** The melting
point of the sample is depressed relative to that of a pure substance, and the mp range
is off by a substantial amount.
List three precautions to take while using the melting point apparatus. **** The
aluminum block of Mel-Temp becomes hot when in use, so it is recommended to not
touch the block.
Avoid overloading the sample as it can affect the accuracy of the melting point
determination.
Do not use with bare hands, especially when placing samples in the apparatus.
When is it important to first perform a rapid determination of mp, followed by an
accurate determination of mp? Why? **** The rapid determination of the mp gives us
an efficient way to assess the approximate mps and confirm what a substance might be,
and the slower more accurate determination allows us to confirm if the observed melting
point aligns with the expected melting point. The accurate evaluation of the mp also
allows us to determine if there are any impurities present in the substance.
To prepare a sample in a capillary tube for a melting point determination, gently tap the
tube into the sample with the ____ end of the tube down. Continue tapping until the
sample ____. Then, with the ____ end of the tube down, tap the sample down slowly or
________ to move the sample down faster. **** 1. Open
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