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Lecture

CHEM 212 Lab Summaries.doc


Department
Chemistry
Course Code
CHEM 212
Professor
Mike Daoust

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Summary of CHEM 212 Labs: a 10 minute review
Experiment 1: Recrystallization
We separate solids by their differences in solubility. In this lab, we want to extract phthalic
acid from its mixture with charcoal (which was used to decolorize the aqueous solution after
phthalic acid was added to it). So we heat up the solution, thereby dissolve the solid. then
we can filter out the charcoal and insoluble solid impurities using hot gravity filtration
We can then recrystallize the solid from its dissolved state by lowering the temperature of
the water (ice bath it after it cools room temperature). And then do the suction (vacuum)
filtration and measure the melting temp range of the yield to determine the purity of the
collected solid.
Notes:
any impurity lowers the melting point.
...why No chemical reaction was involved: only filtering (purifying) the compound.
if no crystallization occurs initially, (a) scratch surface of flask (b) add some of the
original impure material
Experiment 2: Distillation:
Objectives:
Understand that distillation is a technique of separating different liquid components
(with similar solubilities) of a mixture by vaporizing them at different temperatures,
condensing, and collecting them.
Compare effectiveness of simple distillation and fractional
Determine percentage of compositions of two liquid components from experimental
data.
No Chemical reactions~~(just vaporizing and condensing the same cmpds)
We had a mixture of methanol and butanol. These two have very different boiling
temperature (butanol’s is much higher than that of methanol).The goal was to determine the
percentages of components by
1. Use simple distillation to get the rough idea where the boiling temperature changes (i.e.
when most of the liquid component with lower boiling temperature evaporates, condenses,
and get collected. (your midpoint)
2. and then use the fractional distillation to get more precise measurements.
You then calculate the percentages of each components by number of moles, not volume.
Note: on the distillation graph, a perpendicular line from the beginning of the sharp rise (or
midpoint of slope if there is no sharp rise) to the x axis is the volume of methanol.
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