Food Dye Spectroscopy Lab Result | Lab Reports Chemistry

FOOD DYE SPECTROPHOTOMETRY

Revised 10/24/18

OBJECTIVE(S):

• Work individually to apply concepts and use lab skills that have been previously practiced in the

Che-1A laboratory.

• Prepare a series of dilutions

• Prepare a standard absorbance curve using spectrophotometry and identify the concentration of an

unknown solution.

• Introduce concepts of Green Chemistry

INTRODUCTION:

Background

This experiment is designed to allow you more freedom to create your own procedures and to test your

skills on solution preparation and analysis. A procedure will need to be written for the experiment in

order to determine the concentration of a colored food dye, Erythrosin B (Acid Red #3), in an unknown

solution. This is a food dye that is certified by the Food and Drug Administration (FDA) and is

commonly used in coloring maraschino cherries.

Concepts and skills to be used in this experiment that have already been practiced and applied are:

• Using molarity units

• Making solutions

• Doing dilution calculations

• Performing dilutions in the lab

• Using spectrophotometry as an analysis tool to determine absorbance of solutions

• Creating a standard calibration curve

• Determining the concentration of an unknown using a standard absorbance calibration curve

This experiment has been selected as it reflects a goal in the Chemistry Department to change experiments

in order to comply with Green Chemistry objectives in order to be greater stewards of the environment.

According to the Environmental Protection Agency, “Green Chemistry consists of chemicals and

chemical processes designed to reduce or eliminate negative environmental impacts. The use and

production of these chemicals may involve reduced waste products, non-toxic components, and improved

efficiency.” In this experiment, the solutions can be poured down the drain. The savings from the use of

a food dye are both direct and indirect (costs, exposure, and other environmental consequences).

Erythrosin B solution is red in color and absorbs light strongly in the visible region of the electromagnetic

spectrum. Remember that the color seen is the complement of the color absorbed. For example, the

complimentary color of red is green. Therefore, this solution absorbs strongly in the green region of the

spectrum (515-555 nm) and the color seen is its complement, red. The wavelength of maximum

absorbance is 525 nm for the red dye solution.

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Revised 10/24/

OBJECTIVE(S):

Work individually to apply concepts and use lab skills that have been previously practiced in the Che-1A laboratory.
Prepare a series of dilutions
Prepare a standard absorbance curve using spectrophotometry and identify the concentration of an unknown solution.
Introduce concepts of Green Chemistry INTRODUCTION: Background This experiment is designed to allow you more freedom to create your own procedures and to test your skills on solution preparation and analysis. A procedure will need to be written for the experiment in order to determine the concentration of a colored food dye, Erythrosin B (Acid Red #3), in an unknown solution. This is a food dye that is certified by the Food and Drug Administration (FDA) and is commonly used in coloring maraschino cherries. Concepts and skills to be used in this experiment that have already been practiced and applied are:
Using molarity units
Making solutions
Doing dilution calculations
Performing dilutions in the lab
Using spectrophotometry as an analysis tool to determine absorbance of solutions
Creating a standard calibration curve
Determining the concentration of an unknown using a standard absorbance calibration curve This experiment has been selected as it reflects a goal in the Chemistry Department to change experiments in order to comply with Green Chemistry objectives in order to be greater stewards of the environment. According to the Environmental Protection Agency, “Green Chemistry consists of chemicals and chemical processes designed to reduce or eliminate negative environmental impacts. The use and production of these chemicals may involve reduced waste products, non-toxic components, and improved efficiency.” In this experiment, the solutions can be poured down the drain. The savings from the use of a food dye are both direct and indirect (costs, exposure, and other environmental consequences). Erythrosin B solution is red in color and absorbs light strongly in the visible region of the electromagnetic spectrum. Remember that the color seen is the complement of the color absorbed. For example, the complimentary color of red is green. Therefore, this solution absorbs strongly in the green region of the spectrum ( 515 - 555 nm) and the color seen is its complement, red. The wavelength of maximum absorbance is 525 nm for the red dye solution.

Measurement of Absorbance A spectrophotometer (Spec 20) will be used in this experiment to determine the absorbance of light absorbed by the colored Erythrosin B solution (Figure 1). Figure 1 Spec 20 Beer’s Law and the Determination of Concentration of an Unknown In order to find the concentration of an unknown, you will need to make a calibration curve using a set of solutions with known concentrations. Beer’s law shows the relationship between absorbance and concentration as follows: A = e l C where A = Absorbance (no unit) e = molar absorptivity (M-^1 cm-^1 ) l = path length (1.00 cm in this experiment) C = concentration (in mol/L) Some books refer to Beer’s law as just A = b C where “b” combines both the molar absorptivity and path length. When plotting absorbance versus concentration, a calibration curve or standard absorbance curve is established in the form of a straight line since the molar absorptivity (e) is constant for a given substance and the path length ( l ) of the cuvette is constant. The (0,0) point is included in the data when generating the calibration curve as the solvent was used to calibrate the Spec 20 at 100% transmittance which is equivalent to 0 absorbance. Therefore, for 0 concentration of solute zero absorbance is measured. The equation of the line will then be used to calculate the concentration of an unknown upon measuring the absorbance of the unknown. Wavelength filter lever

Figure 2 Example of an absorbance curve with the trend-line forced through zero The slope of the line in Figure 2 is 70, 193 M-^1 cm-^1 and the molar absorptivity times the pathlength is 70,193 M-^1 since the path length is 1.00 cm. The calibration curve shows good linearity as R^2 is very close to 1 (R^2 =0.99556). Figure 2 is an EXAMPLE not necessarily the concentration values needed to generate the curve in this experiment. The calibration curve in Figure 2 shows 6 data points, one at (0,0) and the others uses different solutions of known concentration. Although it is better to have more points on a calibration curve than just two, one must consider time required to do the experiment. Therefore, think of what would be the minimum number of points to generate a decent calibration curve. Also, the absorbance of your unknown must fall within the range of your calibration points. Limit to Linearity of the Spec 20 One must also be aware that instruments have a limit to their linearity. For example, it is common for absorbance measurements to “level off” and no longer remain linear beyond a certain concentration of solution. For the red dye solution, this usually occurs around 0.8 or higher absorbance. For example, in Figure 2, the absorbance starts to level off and the relationship between absorbance and concentration no longer is linear beyond 0.8 absorbance. Figure 3 shows what would happen if one were to continue making more solutions of higher concentration beyond 0.8 absorbance for a red dye solution.

0 2 4 6 8 10 12 Absorbance Concentration (x10-^3 M) y = 70,193 x R^2 = 0.

Figure 3 Calibration curve no longer linear beyond an absorbance of 0.8. When developing your procedure in your lab notebook, it is important to be considerate of a few things. Keep in mind that your procedure has to be detailed enough for someone else to duplicate your experiment even if they have never seen this experiment before. In addition, careful thought must be exercised in your procedure to consider limitations on precision of glassware as this ultimately affects the precision of the standard calibration curve, and hence, your determination of the concentration of your unknown. In addition, the accuracy will be affected by the quality of lab skills and tools utilized. When scientists look at others’ published experimental work, they think about using select procedures and lab glassware that will yield the best precision and accuracy to yield quality results so that the results from the experiment can be trusted. In addition, one might first measure the absorbance of the stock solution used in this experiment to see if it is even near 0.8 absorbance. If it is much higher, a dilution may be required to get the stock solution within range of the linearity of the Spec 20. This can be a difficult task. Therefore, a hint to doing this is to make a solution that is 5 or 10 times less concentrated than the stock solution. Your grade for this experiment may depend on your notebook recording and quality of results (precision and accuracy). Your professor may also require a typed lab report in part or in full. Ask your professor for specific grading criteria.

0 5 10 15 20 25 Absorbance Concentration (x10-^3 M)

CHEMICALS AND MATERIALS

Erythrosin B (Acid Red 3) Stock Solution (molarity approximately 8 .00x10-^5 M) EQUIPMENT TO BE CHECKED OUT 100 mL, 50 mL, 25 mL, and/or 10 mL volumetric flasks can be used (only one type of volumetric flask is allowed per student) 2, 5, 10 mL graduated pipets can be used Pipet bulb or pipet pump Cuvets for the spectrophotometer SAFETY Goggles must be worn at all times in the bench and working areas of the laboratory whenever anyone is working. If goggles become clouded, go to the non-bench area of the lab, remove goggles, and clear them. Goggles may be removed in the seating area of the laboratory. Keep solutions away from skin or face, and wash off immediately if chemicals touch the skin. WASTE DISPOSAL All solutions may be poured down the drain EXPERIMENTAL PROCEDURE: This experiment is designed for students to work independently from one another. Do not consult with students during this lab experiment. Be aware that you may only have two lab periods to make a calibration curve and determine the concentration of an unknown. Therefore, you will need to be efficient and work quickly. Rinse any glassware that was used with the dye solution immediately when you are finished using it as the dye can be difficult to clean from glassware. Part 1: Calibrate the Spec 20 and Check absorbance of a diluted red dye solution Write a procedure for part 1 for calibrating the Spec 20, making a dilution and measuring the absorbance of the diluted red dye solution. Use the following to help you write your procedure:

What is the solvent used in this experiment?
Review prior experiments for further details for a. calibrating the Spec 20 b. how to generate a calibration curve
Record the true molarity of the stock solution from the label on the bottle.
Make a dilution of the stock solution so that the concentration is about 8 .00x10-^6 M.
Measure the absorbance of the diluted red dye solution about 8.00 x10-^6 M.

All information needs to be recorded in your notebook (observations, notes, calculations, units, etc.). Remember, more detail is better than too little detail.
Have your instructor check your procedure before starting the experiment. Part 2: Creation of a Calibration Curve (Standard Absorbance Curve) Write a procedure for part 2 for creating a calibration curve using the dilute red dye solution that you made in part 1. Use the following to help you write your procedure:
Decide on how many data points you wish to have to create your calibration curve. a. Two calibration points are too few as any line is perfectly linear with just two points. It does not show any degree of error and is not appropriate. Five is probably too many as you only have one period to finish this experiment. b. You may use the diluted red dye solution ( about 8 .00 x 10-^6 M) for your first calibration point if it is appropriate. If not, make any necessary dilution. c. For the other calibration points, make appropriate dilutions of the diluted dye solution about 8.00 x 10 -^6 M) or the solution that was used to make your first calibration point using appropriate glassware to cover a broad range of absorbance values between 0.0 and 0.8.
All information needs to be recorded in your notebook (observations, notes, calculations, units, etc.). Remember, more detail is better than too little detail.
Have your instructor check your procedure before starting the experiment. Part 3: Molarity of Unknown Solution Write a procedure for part 3 for measuring the absorbance of your unknown as well as determining the concentration of your unknown. Use the following to help you write your procedure:
Ask your instructor how many unknowns will be used for your experiment. Obtain your unknown(s) from your instructor by providing them with a clean, dry test tube(s) labeled with your first name and last initial with the tape from the instructor bench. The instructor will return your test tube(s) to you containing your unknown solution with the unknown number written on the test tube. Or your instructor may provide you with the unknown. Either way, it is crucial to record your unknown number in your lab notebook.
Measure and record the absorbance of the unknown. If it is outside the calibration range, you may need to perform a dilution on the unknown. A rule of thumb for dilutions is using factors of
In other words, try diluting your unknown by making it 10 times more dilute and measure the

Are there any health concerns when consuming food dyes? You may have to look at other sources to answer this question. Be sure to cite all references used. Comment on the validity of the resources if they are from the internet.
Identify why it might be better to use a food dye instead of another type of colored solution such as a Na 2 Cr 2 O 7 solution from an environmental or green chemistry perspective. You may have to research this with additional resources from books and/or the internet. If you use additional resources, be sure to cite the resource(s) at the end of your answer. If internet resources were used, how reliable is/are the resource(s)? In addition, identify which green chemistry principles might apply to your answer. See green chemistry principles below (from http://www.epa.gov/sciencematters/june2011/principles.htm): 1. Prevention It’s better to prevent waste than to treat or clean up waste afterwards. 2. Atom Economy Design synthetic methods to maximize the incorporation of all materials used in the process into the final product. 3. Less Hazardous Chemical Syntheses Design synthetic methods to use and generate substances that minimize toxicity to human health and the environment. 4. Designing Safer Chemicals Design chemical products to affect their desired function while minimizing their toxicity. 5. Safer Solvents and Auxiliaries Minimize the use of auxiliary substances wherever possible make them innocuous when used. 6. Design for Energy Efficiency Minimize the energy requirements of chemical processes and conduct synthetic methods at ambient temperature and pressure if possible. 7. Use of Renewable Feedstocks Use renewable raw material or feedstock rather whenever practicable. 8. Reduce Derivatives Minimize or avoid unnecessary derivatization if possible, which requires additional reagents and generate waste. 9. Catalysis Catalytic reagents are superior to stoichiometric reagents. 10. Design for Degradation Design chemical products so they break down into innocuous products that do not persist in the environment. 11. Real-time Analysis for Pollution Prevention Develop analytical methodologies needed to allow for real-time, in-process monitoring and control prior to the formation of hazardous substances. 12. Inherently Safer Chemistry for Accident Prevention Choose substances and the form of a substance used in a chemical process to minimize the potential for chemical accidents, including releases, explosions, and fires.
What part(s) of the experiment was the most difficult to?
What part(s) of the experiment was the easiest to do?
Did you experience any problems during this experiment? If so, identify the problems.
Did you feel that the prior experiments in Che-1A prepared you for this experiment? If so, which experiments helped the most? If not, what could be done differently for us to improve the experiments in this course to better prepare you for the lab practicum.

REFERENCES:

Written by Jody Williams Tyler with helpful contributions from discussions with Tatiana Lopez, Kamran Golestaneh, and Terri Beam and review comments by Terri Beam and Kamran Golestaneh from the Chemistry Department at Mt. San Antonio College. Stock, J.L., J. Chem. Ed ., 1995, 72 (10), p. 926. Beam, T., “Copper Concentration”, Chemistry 50 Laboratory Manual, Mt. San Antonio College, Fall 2012, p. 129.

Attach the calibration curve and any table(s) of data.
Identify any sources of error in the experiment:
Identify any possible areas for improvement:
Attach the answers to your post-lab questions to this sheet.

Food Dye Spectroscopy Lab Result, Lab Reports of Chemistry

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OBJECTIVE(S):

CHEMICALS AND MATERIALS

REFERENCES: