Exploration 1

CHEM 211-2008
Experiment 2
Week 2
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Gas Chromatogram
How is the
Boiling Point of a
Mixture of
2 Liquids Related to
the Boiling Points of
the Pure Liquids?
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Abbe Refractometer
A. Pre-lab Preparation Assignment:
1. Read: -This handout
-Operation: 32: Refractive Index (Padías pp. 45-46 & 58-62)
-Operation: 34: Gas Chromatography (Padías pp. 150-151 & 173-175)
2. Complete the Prelab Questions on the course website by 7:00 PM, Sunday, September 14.
3. Consider possible responses for the QOW (See below)
4. In your lab notebook: (See Lab Manual pp. 16-19 for format.)
Treat Week 2 as a continuation of Experiment 2. Enter the Question of the Week after
your notes from the Week 1 prelab discussion.
5. Bring your notebook and your ideas to the Monday Lab Discussion period. Record your
Week 2 pre-lab discussion notes after the QOW for Week 2.
B. Introduction:
In Experiment 1 you explored the effects of changes in structure on the boiling point of a
pure liquid. Last week, you extended this discussion to consider mixtures of liquids. You
combined two liquids and observed the boiling point behavior of the mixture during a
distillation. The result showed a significant effect of difference in the boiling points of the
components of the mixture on the boiling point behavior over the course of the distillation.
This week you will explore the composition of the distillate at different points in last week’s
C. Question of the Day:
How is the composition of distillate from a mixture of liquids related
to the bp at which it was collected?
Will the composition of the distillate collected from distillation of a mixture be the same as
that of the original mixture or different? Will the composition of the distillate change as the
bp at which it is collected changes? If the composition of the distillate is different from that
of the original mixture, which of the original compounds would predominate? Would the
identity of the predominant component change with changes in the bp at which the distillate
is collected?
CHEM 211 Experiment 2-WK-2
Boiling Points and composition of mixtures
On Monday after discussing the results of the distillations in Experiment 2 – week 1, we will
collect reasonable hypotheses about the QOW and explanations of the logic that led to each
proposal. We will then have a brief discussion of the two new analytical methods, refractive
index and gas chromatography, that you will use to analyze the composition of the distillate
fractions you collected last week. In the lab you will do the analyses and determine if the
compositions of fractions are related to their boiling points.
D. Key Terms/concepts/techniques:
 Boiling point
 Refractive Index
 Gas Chromatography
 Percent Composition
D. Safety Matters:
a. Safety glasses are required.
b. No sandals or open-toe shoes
E. Waste Disposal:
Non-halogenated organic liquids
Halogenated organic liquids
Category 4
Category 3
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