This lab procedure requires a UV/Vis Spectrometer which is not available in lab kits. For this lab you will be given the Procedures and data for an actual experiment. It will be your job to analyze the data and write a report on it as if you performed the lab yourself.
Lab format: this lab is a simulated lab activity.
Relationship to theory: This activity is designed to be done after a basic introduction to the BeerLambert Law. It introduces the idea of solving simultaneous equations for multiple unknowns.
LEARNING OBJECTIVES
- Solve simultaneous equations for multiple unknown concentrations.
- Determine and report the concentrations of two food dyes in a sports drink, along with associated experimental uncertainty (error)
- Determine the major sources of uncertainty in this experiment.
DATA
Shown below is a photo of the three drinks that were analyzed.
Figure - Drink samples from left to right Drink #1, Drink #2 and Drink #3
These solutions were analyzed with a spectrophotometer that had been blanked with distilled water. The path length was 1.0 cm. Absorbance values were recorded at 629 nm and 427 nm.
Data from three trials is presented in Table I.
| Drink #1 |
Abs at 629 nm |
Abs at 427 nm |
| Trial 1 |
0.005 |
0.317 |
| Trial 2 |
0.008 |
0.324 |
| Trial 3 |
0.01 |
0.322 |
| Drink #2 |
|
|
| Trial 1 |
0.355 |
0 |
| Trial 2 |
0.358 |
0.001 |
| Trial 3 |
0.339 |
0.001 |
| Drink #3 |
|
|
| Trial 1 |
0.257 |
0.206 |
| Trial 2 |
0.253 |
0.21 |
| Trial 3 |
0.258 |
0.199 |
Data from three trials is presented in Table I on the next page.
1. Use this data and the equations and information given on pages 4 and 5 of this handout to find the AB1 and AY5 values for each trial and for each drink. (Do not average the values before calculating or at this point)
2. Use the individual AB1and AY5 values to find the concentration (M) of yellow dye and blue dye in each of the drinks.
3. Convert the concentrations to μM.
4. Average the three trials for each dye and find the standard deviation. (You may use Excel for the average and standard deviation calculation). Correctly report these values in your lab report.
Questions (show all necessary calculations):
1. How are the dyes called Blue #1 and Yellow #5 similar to each other? How are they different? (Be sure to discuss functional groups.)
2. What ionic group does Yellow #5 have that Blue #1 does not?
3. Describe in your own words what the "molar absorptivity" of a molecule is.
4. Record the average concentrations of the dyes (in μM) from each drink including uncertainty. (Be sure to show work for these in your calculation section of your report.)
5. If Drink #3 contains 2.5 μM Blue #1 and 7.5 μM Yellow #5, calculate the percent error.
6. How many significant digits can you report in the concentration of the unknown sample? What limits the number of significant digits in this result?
7. Use Figure 3 to determine what color light is being absorbed at λmax for each dye. Is this what you would expect based on the color of the drinks in Figure 3?
Color at Blue#1's λmax: _________________________________
Color at Yellow #5's λmax: ___
Figure - Visible portion of EM Spectrum