Project 13
Analysis of Cola
Michelle Pryce
Chemistry 101 Laboratory, Section
Instructor: Sabina Maskey
07 November 2007
My signature below indicates that this document represents my own
work. Excluding shared data, the information, thoughts, and ideas are
my own, except as indicated in the references.
Michelle Pryce
Abstract:
This purpose of this experiment is to analyze the phosphate content of three different
colas using a spectrophotometer.
be done.
In order to accomplish this task, several things must
First, proper usage of the spectrophotometer must be determined.
Then the
spectrophotometer must be used in order to determine the relationship between the
color of a compound and the wavelength of light absorbed.
Once a relationship has
been determined, a correlation between the amount of light absorbed and the
concentration of phosphate in the solution must be determined.
Several different
experiments were conducted in order to analyze the phosphoric acid content since
phosphoric acid cannot be directly measured.
After several weeks of investigation, both
goals of the project were met, and it was determined that Diet Coke had the greatest
concentration of phosphate among the three colas tested.
Introduction:
Background:
This research group has been transferred to a major cola company.
The company has decided to engage in industrial espionage in order to look at the
formula for the rival’s cola products.
The major ingredient that the company is
interested in is the phosphate content of the colas, since many people drink cola
because they think the buffering capacity of the phosphate will help to settle their
upset stomach.
The purpose of this research is to analyze as many of the rivals’
coal products as possible
(lab manual, 2005).
There were two goals to this research project.
accurately use the spectrophotometer.
The first goal was to learn how to
In learning to accurately use the
spectrophotometer, two distinct relationships must be determined.
The first relationship
that had to be determined was the relationship between color of a compound and the
wavelength of the light absorbed.
had to be determined.
Once that was determined, a second relationship
The second relationship was the correlation of the amount of
light absorbed with the concentration of the solution.
Once those relationships were
established, then the second goal of determining the amount of phosphate contained in
each sample of the competitor’s cola could be analyzed.
This experiment consisted of four parts.
Part one consisted of determining the proper
use of the spectrophotometer and using it correctly to determine the relationship
between color and wavelength of absorbance.
Part two consisted of making solutions
of different colors and measuring them in the spectrophotometer at several different
wavelengths in order to determine the relationship between color and absorbance.
Once part two was completed, part three could begin.
In part three the determination
of the relationship between absorbance and concentration was established.
Finally,
once the concentration of solutions that contained colors was clarified, then that data
could be used to analyze the phosphoric acid content of the samples of cola.
Results:
Part one:
The first part of this experiment was to learn how to properly use the
spectrophotometer.
A sample with known transmittance and absorbance values was
measured to determine the accuracy of the spectrophotometer.
Once the accuracy of
the known values had been verified, then the actual experiments could begin.
Part two:
In part two of the experiment, the relationship between color and wavelength of
absorbance could be measured.
samples had to be prepared.
In order to perform an analysis of color, the
The samples were prepared as follows:
Sample 1—
blank, consisted only of water, sample 2—one drop of red food color mixed into 100
mL of water, sample 3---one drop of blue food color mixed into 100mL of water,
sample 4---a 1:1 mixture of the red and blue solutions, and sample 5—0.001M KMnO4
from
1mL of 0.004M of KMnO4 and 3ml of water.
The samples were tested in the
spectrophotometer at wavelengths ranging from 350 nm to 700 nm at 25nm increments.
The spectrophotometer was blanked in between each increase of wavelength.
are summarized in table 1and graph1.
Results
Absorbency and molarity at 525nm were
determined and results were summarized in table 2 and chart 2.
Part three:
In part three of this experiment, the relationship between absorbance of light and
concentration of solution was investigated.
The relationship was determined to be
inversely proportional.
increased.
As concentration of a sample was decreased, absorbance
This relationship makes sense because samples that are too heavily
concentrated are much darker in color than diluted samples, and therefore absorb all
light emitted from the spectrometer giving no reading. These results were summarized
in the table and graphs section.
Part four:
In part four of the experiment the phosphate content of the colas could finally be
determined.
In order to accomplish the task, the colas first had to be prepared.
The
carbon dioxide had to be removed, and the cola had to be diluted in order to obtain
meaningful readings.
Since phosphoric acid does not absorb UV light a solution of
AVM was added to the diluted colas so that the phosphoric acid could be measured.
Discussion:
This was a multi faceted experiment to determine the phosphate content in several
varieties of colas.
However, phosphate content could not be directly measured so a
series of experiments were devised in order to assist in the development of the new
cola product.
It was hypothesized that people consume cola because of the phosphate
contained in the product acts as a buffer against stomach acid.
In order to confirm
or deny if this hypothesis is correct, a comparison of phosphate content of known
medications for upset stomach such as pepto bismol and cola should have been done.
In the absence of such a comparison, it cannot be proven or disproven that people
drink cola solely to assuage an upset stomach.
Part one:
Part one of the experiment consisted only of the calibration of the equipment. A
sample with known values was placed in the spectrophotometer and the reading of
absorbance and percent transmittance were taken and compared to the known values.
This was a critical step for the entire project as the calibration of the
spectrophotometer was of vital importance as it was the main piece of equipment used
in this project.
Part two:
In part two of the experiment, the relationship between color and wavelength of
absorbance was determined.
Four samples of four different colors were prepared as
described in the experimental section.
graphs section.
Results are summarized in the tables and
Measurements were taken at several increments of the light spectrum
in order to determine the point of maximum absorbance.
As a reminder, the point of
maximum absorbance is not the same as the color of the sample.
These results
were compared to the table on page 89 of the lab manual (Cooper, 2005) in order to
determine the relationship between color of light and wavelength of light.
Another important aspect of this portion of the experiment was the determination of the
relationship between transmittance and absorbance.
Transmittance is defined as the
number of photons that pass through the sample without being absorbed (Cooper,
2005) while absorbance is usually thought of as the opposite of transmittance.
In fact,
the mathematical relationship between absorbance and transmittance can be expressed
in the following formula:
Part three:
A=2.000-log (%T) (Cooper, 2005).
Part three adds another layer of complexity to the experiment.
In this section of the
experiment, the relationship between the absorbance of light and concentration (molarity)
of solutions were investigated.
Concentrations of most everyday items are way too
concentrated to be analyzed in the spectrophotometer.
For this reason, samples used
to measure concentration must be diluted in order to be measured.
diluted, the molarity of the solution is decreased.
As samples are
This relationship is illustrated in the
tables and graphs section.
Part four:
All previous experiments have produced information needed to measure the phosphate
content in the colas.
spectrophotometer.
The colas must be diluted in order to be analyzed in the
At shelf concentration, the sample is much too concentrated to be
measured by the equipment.
an indicator was added.
vanadomolybdate.
Once the cola was diluted to a useable concentration,
For this experiment, the indicator used was ammonium
AVM was added to the solution because phosphoric acid cannot
absorb ultraviolet or visible light.
However, with the indicator added, the solution
undergoes a chemical reaction that allows phosphoric acid to be measured.
Experimental Section:
Part one:
The spectrophotometer was turned on and allowed to warm up for a minimum of 10
minutes.
Two solutions were prepared.
The first solution prepared was a blank.
The
blank only contained the solvent and the known sample contained the solvent and the
solution.
The difference in the amount of light absorbed between the blank and the
solution is the absorbance amount since the absorbency of the solvent was the same
in both samples.
The blank was placed in the spectrophotometer and % transmittance
(%T) was set to 0.
Then a blank cuvette was placed in the spectrophotometer.
Then % T was set to 100%.
obtained.
Once the machine was calibrated, readings could be
The process had to be repeated for each change in wavelength.
This
process allowed a known sample to be measured in the spectrophotometer to access
the accuracy of the device.
Part two:
Four different colored samples were made and tested in the spectrophotometer.
The
samples were tested at several different wavelengths and the absorbance was recorded
in table 1.
Sample 1 consisted only of water and was used as the ‘blank’.
Sample 2 was made from adding 1 drop of red dye to 100 ml of water. Then the
solution was stirred and poured into a 10ml flask.
solution from the 10ml flask.
100 ml of water.
A cuvette was filled with the red
Sample 3 was made from adding 1 drop of blue dye to
Then the solution was stirred and poured into a 10ml flask.
Sample 4 was made by taking 1:1 ratio of red solution and blue solution and mixing
them together.
Sample 5 was made by diluting 0.004M KmnO4 into 0.001M KmnO4
and then adding 1ml of solution to 3ml of water. These four colored samples were
analyzed at wavelengths ranging from 350nm to 700nm at 25nm increments.
Part three:
The third step of this experiment consisted of two parts.
Part one was
the determination of the analytical wavelength of phosphate and AVM and part two
was the creation of a calibration curve of phosphate/avm using %T vs. molarity and A
vs. molarity.
In order to accomplish this portion of the experiment, the stock KH2PO4
(M=0.101) had to be diluted.
In order to achieve the final concentration of 0.0002M,
the stock was diluted in two separate steps first going from 0.101M to 0.005M and
then going from 0.005M to 0.0002M using the M1V1=M2V2 formula.
Once the final
concentration of 0.0002M KH2PO4 was achieved, then the maximum point of absorbance
could be determined (see table % T 350-650).
Calibration curves were drawn for
phosphate/avm using %T vs. molarity and A vs. molarity values.
Part four:
In order to accomplish the task, the colas first had to be prepared.
In order to
prepare the colas for analysis, dissolved carbon dioxide had to be removed from the
cola.
The colas were boiled for approximately 20 minutes in glass beakers.
glass was placed on top of the beakers in order to minimize evaporation.
A watch
Then the
colas were diluted by a 50:1 ratio (50 mL of water and 1mL of cola) and 10 mL of
diluted cola was mixed with 5mL of AVM.
A sample of each cola/AVM mixture was
placed in four separate cuvettes and each sample was measured in the
spectrophotometer.
(Note:
The results for the 400nm wavelength are summarized in table 8
The wavelength of maximum absorbency was determined to be 350nm, but the
spectrophotometer would not allow the samples to be measured at wavelengths less
than 400nm.
well.
Samples were prepared multiple times and checked multiple times as
The error was determined to be a malfunction of the spectrophotometer and the
experiment was allowed to continue using the closest wavelength available which was
400nm).
Conclusion:
Several experiments were conducted in order for the company to spy on its
competitors.
All goals of the experiment were met including learning to use the
spectrophotometer, determining the significance of relationship between absorbance,
wavelength and concentration, and analyzing the phosphate content of all of the
samples of the competitors’ products.
greatest phosphate content.
It was concluded that Diet Coke had the
In order for the new product to have a greater buffering
capacity against stomach acid than Diet Coke, the new product should have higher
phosphate content than Diet Coke.
The researchers also learned how to effectively
use the new spectrophotometers in order to conduct research and analysis.
References:
Cooper, M M. Cooperative Chemistry Laboratory Manual. 3rd
edition, 2005.
www.msds.gov
-ammonium vanadomolybdate
-potassium permanganate
-KH2PO4
Periodic Table of the Elements. SparkCharts. 2002.