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CHE106: C h e m i c a l
Gas Chromatography and
Organic Models
S c i e n c e
C o n c e p t s
Name
Partners
Date
Objectives
o To separate two different alcohols using gas chromatography
o To identify the components of a mixture by using both
reference standards and retention time comparison
o Create a calibration curve on graph paper using the
percentage of the ethanol peak for each of the known
mixtures.
o To calculate the percentage composition of the mixture
o Build and analyze models of simple and complex organic
compounds
Gas Chromatography (GC)
EXPERIMENTAL: The GC experiment consists of graphing the GC data
obtained from standard solutions with known concentrations. This
graph is called a calibration graph or calibration curve. It
will be used to determine the ethanol concentration of an
unknown solution. The instrument is a Gow Mac chromatograph
equipped with a thermal conductivity detector and a chart
recorder. The standard solutions have been prepared in advance
(5%,10%,15%, 20%, 25% ethanol in 2-propanol). Every student will
be given the chromatograms of the standard solutions so that the
retention times and peak heights can be measured. The data table
will be completed and a graph of peak height vs. concentration
using this data will be created. Each student will inject a
sample of unknown concentration. The peak height measurement
from this chromatogram will enable you can determine the
percentage composition of your unknown sample.
Lab report: Complete the data sheet, staple the chromatogram and
calibration graph to this handout and complete the organic
models report section.
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GC Data Sheet
1. Measure the distance from the injection point to the middle
of each peak in millimeters (mm) for the 5% solution and the 20%
solution. Record this number in the tables below.
5% solution
Name of
alcohol
Ethanol
Peak
2-Propanol
2
Distance(mm)
Retention
time
Distance(mm)
Retention
time
1
20% solution
Name of
alcohol
Ethanol
Peak
2-Propanol
2
1
.
2. The paper was moving at a speed of 20 mm/min(chart speed).
Use this value to convert the distance (mm) you measured to time
(minutes). This value tells you how many minutes it took for the
sample to travel through the column and it is known as the
retention time. Record this value in the table above. Show your
work for credit.
Conclusion:
Is the retention time of ethanol dependent upon
concentration?__________
Explain.
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GC Data Sheet
3. Measure the height of the first peak on the chromatogram of
each of the different concentration. Record the height in the
table provided below.
Height(mm)
0
% concentration
0
5
10
15
20
25
4. Create a X/Y graph using the website “Create a graph” and the
data in the table above.
The X-axis is height and the y-axis is % concentration, source
is your name. Attach your graph to your report.
http://nces.ed.gov/nceskids/createagraph
5. Measure the height of the ethanol peak (first peak) on the
chromatogram of your unknown. Use your graph to determine the
concentration of ethanol in your unknown sample.
Unknown: _______________
Concentration of ethanol: _______________________________
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Organic Models
Working with molecular models is extremely helpful in
visualizing organic compounds. The arrangement of atoms in space
is quite different from the way we draw them. This spatial
arrangement turns out to be vital (literally); atoms may have
the same sequence, but not the same biological activity. Large
molecules have many possible spatial arrangements. Do not
regard this exercise as child’s play; Watson and Crick won a
Nobel Prize for working out the structure of DNA using models.
Children enjoy it too.
Experimental: The set of model atoms we are using has colored
wooden balls, which are connected with pegs and springs. At the
end of the period, make sure all bonds are removed and the model
kit is in the same condition that you found it. A bin of extra
balls is available so you can adjust the numbers of each.
Pliers are available to remove pegs. Use the appropriate color
ball for the elements when constructing your models.
Carbon:
Hydrogen:
Oxygen:
Nitrogen:
black
yellow
red
blue
Bromine: orange
Chlorine: green
Fluorine: violet
Because hydrogen atoms are so small, use shorter pegs for all
bonds to H atoms (yellow balls). Long pegs are used for all
other single bonds. Two springs are used for a double bond, and
three springs for a triple bond. Do not use a single spring to
represent a single bond.
NOTE: Carbon always forms four bonds, counting double and triple
bonds as two and three bonds each; hydrogen forms one bond;
oxygen forms two bonds and nitrogen forms three bonds. Build the
following compounds and have your instructor initial each
section of your report.
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1.
Methane – Use short pegs to connect four atoms of H
(yellow) to an atom of C (black). The actual shape of a carbon
compound with only single bonds is called tetrahedral. We
represent the structural formula on paper as if it were flat,
square planar, with 90° angles because it is easy and convenient
to draw the compounds this way.
H
H
H
C
H
C
H
H
H
H
Square planar
Tetrahedral
Ethanol and 2-propanol are the alcohols used in the GC
experiment. Although the compounds contain the same functional
group, their biological properties are quite different. Ethanol
is found in alcoholic beverages whereas 2-propanol is rubbing
alcohol and is quite poisonous if ingested.
2.
Ethanol – Build a model of ethanol CH3CH2OH. Connect the
carbon atoms with a long peg. Draw the structural formula (not
a picture of your model) of ethanol in the space provided.
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OH
3.
2-Propanol – Build a model of 2-propanol, CH3CHCH3.
Notice that the carbon chain is not straight, although we draw
it as straight for clarity and the “OH” is connected to the
second carbon of the chain. Draw the structural formula.
Show your models to your instructor before you dismantle them.
Does it matter which carbon has the OH bonded to it?__________
Explain.
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Many organic and biochemical compounds possess the property of
“handedness” and are called stereoisomers. Compounds containing
a carbon atom bonded to four different elements are “handed” and
are easily recognized. The fact that “handed” molecules are
nonsuperimposable mirror images give many of these compounds
special properties. All naturally occurring carbohydrates,
proteins and enzymes are handed. Many drugs such as ibuprofen,
LSD, methamphetamine and antibiotics are “handed” as well.
4. Stereoisomer – Build models of the two compounds that are
shown below paying particular attention to the bond orientation.
Are the compounds nonsuperimposable? _______________
H
F
F
C
C
H
Br
Br
Cl
Cl
a. Replace a bromine atom (Br-orange ball) with a hydrogen atom
(yellow ball) in both of your structures. Are the compounds
nonsuperimposable? ________________ Explain your answer.
Show your models to your instructor for credit.
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5.
Build one compound from the list below (a- f) and show it
to your instructor for credit.
a. Aspartame (also known as Nutrasweet) is a synthetic dipeptide
that is 200 times sweeter than sucrose (table sugar).
O
H
C
HO
O
NH2
H
N
C
C
H2
C
C
H
O
OH
H2C
b. d-Methamphetamine is a stimulant and resembles amphetamine,
the active ingredient in prescription diet pills.The d-isomer,
shown below has the stimulant effect whereas it mirror image
does not.
CH3
H
H2N
C
C
H2
c. Splenda(sucralose) is an artificial sweetner that is 60,000
times sweeter than sucrose
CH2OH
Cl
O
OH
O
OH
OH
O
OH
ClH2C
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d. TNT= 2,4,6-trinitrotoluene is considered a high explosive
used mostly in military and commercial blasting.
CH3
O2N
NO2
NO2
e. Procaine also known as Novacain is a local anesthetic.
O
C
NH2
OCH2CH2N(CH2CH3)2
O
f. Luminol gives off a photon of light in the presence of
hydrogen peroxide, iron and blood. It is used to detect traces
of blood even after the area has been cleaned.
NH2
O
NH
NH
O
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