CHML211
Exp. 2 Distillation and Gas Chromatography of Alkanes
IN-LAB ASSIGNMENT: (EACH STUDENT will record the following data in his/her laboratory notebook in a well organized
manner during lab period. Yellow carbon copies will be submitted for grading along with Post-Lab assignment.) …..max
score = 20 pts.
6. Data/Calculations (The following information should be recorded directly into laboratory notebook.)
a.
b.
c.
d.
e.
f.
Record which unknown was used
Record distillation range of each fraction collected
Record GC vial slot number for fraction #1
Record GC vial slot number for fraction #4
Record GC sample solvent used
Show all adjusted area percent calculations using your actual GC results
7. In-lab Questions (The following questions should be answered in laboratory notebook.)
a.
How does the shape of an alkane affect the surface area and intermolecular forces between alkane
molecules? What affect does this have on the boiling point of an alkane?
b.
All of the structures shown below have the molecular formula C6H14. Copy the structures into your laboratory
notebook. Look up the boiling point of each compound and record the value under the name of each
structure. Circle the structure which you would expect to have the highest boiling point. Draw an “X”
through the structure which you would expect to have the lowest GC retention time.
n-hexane
2,2-dimethylbutane
2-methylpentane
2,3-dimethylbutane
CHML211
Exp. 2 Distillation and Gas Chromatography of Alkanes
POST-LAB ASSIGNMENT: (EACH LAB GROUP will submit one copy of a typewritten, paragraph style report addressing
all of the points listed below. Must be written using PAST TENSE, PASSIVE VOICE. ) …..max score = 50 pts.
8. Experimental (Write 1-2 paragraphs including all of the following. Do NOT present a bulleted outline.)




Describe the set up of the simple distillation apparatus.
Describe the simple distillation process, including the following:
o The unknown letter and volume of unknown used
o How many samples were collected
Describe the preparation of the GC samples for analysis, including the following:
o Which samples were analyzed, and what vial slot numbers were used
o The identity of the GC solvent used to prepare the samples
Describe the process of analyzing the GC results, including the following:
o How were alkanes present in the unknown solutions identified?
o How were the quantities of each alkane determined for each sample?
9. Results (Complete tables. Once complete, copy and paste the completed tables into your document.)
Table 2.1 Distillation results
Distillation Range
(oC)
Ti
Tf
Fraction #
1
2
3
4
5
XXX
Table 2.2 GC Results
Fraction #1
Peak
#
Alkane
Identity
Standard
Rt
(min)
Sample
Rt
(min)
Area
%
Fraction #4
Adjusted
Area %
Sample
Rt
(min)
Area
%
Adjusted
Area %
1
2
3
10. Discussion (Write 1-2 pages addressing all of the following points.)





Which unknown letter was used, and what alkanes were present in the unknown sample? Give the standard
retention times for these alkanes, and the sample retention times for the alkanes present in both samples that
were submitted for analysis.
How much of each alkane was present in the Fraction #1 sample? How much of each alkane was present in the
Fraction #4 sample? Give adjusted area % values for the alkanes from each sample submitted for analysis.
Based on the GC results, were the alkanes separated completely by the end of the simple distillation method?
How was this conclusion reached? What does this indicate about the efficiency of this separation method?
Include a short comment addressing what could be done differently to improve the experimental results, if
repeated.
Be sure to attach GC sample chromatograms!