Project 13



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. In order to accomplish this task, several things must be done. 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. The first goal was to learn how to accurately use the spectrophotometer. 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. Once that was determined, a second relationship had to be determined. 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. In order to perform an analysis of color, the samples had to be prepared. 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. Results are summarized in table 1and graph1. 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. As concentration of a sample was decreased, absorbance increased. 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. Results are summarized in the tables and graphs section. 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: A=2.000-log (%T) (Cooper, 2005).

Part three:

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. As samples are diluted, the molarity of the solution is decreased. 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. The colas must be diluted in order to be analyzed in the spectrophotometer. At shelf concentration, the sample is much too concentrated to be measured by the equipment. Once the cola was diluted to a useable concentration, an indicator was added. For this experiment, the indicator used was ammonium vanadomolybdate. 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%. Once the machine was calibrated, readings could be obtained. 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. A cuvette was filled with the red solution from the 10ml flask. Sample 3 was made from adding 1 drop of blue dye to 100 ml of water. 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. A watch glass was placed on top of the beakers in order to minimize evaporation. 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. The results for the 400nm wavelength are summarized in table 8 (Note: 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. Samples were prepared multiple times and checked multiple times as well. 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. It was concluded that Diet Coke had the greatest phosphate content. 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.



-ammonium vanadomolybdate

-potassium permanganate

-KH2PO4

Periodic Table of the Elements. SparkCharts. 2002.

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