Chem 220L
Orange Coast College
GC Analysis of Cyclohexane/Toluene Mixtures
Name
Date
Lab Section Day/Time
Data Table 1:
Number of GC Used ____________________
Sample
Peak 1 (cyclohexane)
Retention Time
Peak 1 (cyclohexane)
Area
Peak 2 (Toluene)
Retention Time
Peak 2 (Toluene)
Area
SD-1
SD-res
FD-1
FD-res
We would like to use the areas to determine the relative amounts of each substance. However, the FID gives
different areas for the same amount of different substances. The relationship between the area of a peak and the
absolute amount of the substance is called the “Response Factor.” In detailed analytical work, the instrument is
calibrated to determine the absolute response factors for the substance of interest. We will instead use a premade
solution of known composition to determine the “Relative Response Factor” (RRF).
First we will calculate the mol % composition of a known mixture. This mixture will consist of 500.0 ml of
cyclohexane and 500.0 ml of toluene mixed together. We will need to know the density and molar mass of the
two substances. These are provided in the following table:
Substance
Cyclohexane
Toluene
Density
0.779 g / ml
0.865 g / ml
Molar Mass
84.16 g / mol
92.14 g / mol
Chem 220L
GC Analysis
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Using these numbers we can calculate the mol % of cyclohexane and toluene in our standard mixture. Complete
the following table. Show your calculations below. Clearly label each separate calculation, and use proper
significant figures and a vertical dashed line. Truncate your answers to one extra, non-significant figure.
Mol of Cyclohexane
Mol of Toluene
Total Mol (cyc+tol)
Mol % Cyclohexane
Mol % Toluene
The next table has the data from a measurement of our standard solution on each instrument (GC#1 and GC#2):
(ask your professor for these numbers).
Area % Cyc
Area % Tol
GC #1
GC #2
Examining the data, we see that the area % of cyclohexane is not the same as its mol % We will assume that the
relative response factor of toluene is 1.000 and then calculate the relative response factor of cyclohexane.
To do the calculation, we first need to examine the formula for calculating the mol % of toluene:
%
.
100
Below, rearrange the above algebraic equation to solve for the relative response factor of cyclohexane (RRF).
Write your result in the space below:
Chem 220L
GC Analysis
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Now we will use the data from the standard to determine the RRF of cyclohexane for each instrument. Because
the cyclohexane and toluene peaks are so much larger than the other peaks, we can use the area % as if they were
the actual areas. Using the area % value for cyclohexane and toluene given above, and the mol % toluene from
our earlier calculation, substitute into your rearranged equation for the RRF of cyclohexane and calculate a value.
Show the setup and calculation for GC #1 and GC#2 in the space below. Then complete the table below for both
GC’s.
RRF of cyclohexane
RRF of toluene
GC #1
1.000
GC #2
1.000
Now we can correct our measured data and calculate the mol % of cyclohexane and toluene measured in our
samples. Calculate the corrected value of the area of cyclohexane (RRF x Measured Area) and record in the table
below. Then calculate the mol % of cyclohexane and toluene, and record in the table below. Show all work on a
clearly labeled calculation on a separate piece of paper.
Area of
Toluene
Sample
Area of
cyclohexane
Corrected
Area of
Cyclohexane
Corrected
Total Area
Mol %
Cyclohexane
Mol %
Toluene
SD-1
SD-res
FD-1
FD-res
Compare your results using GC to your results from refractometry. Discuss the accuracy of the GC (assume the
refractometry numbers are the best available numbers).
Attach your conclusion, GC reports, and calculation pages to these worksheets and submit to your instructor.
Chem 220L
Conclusion:
GC Analysis
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