Lab 10 - Lab 10 Report PDF

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Lab 10 Report ...

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Chem 125 Lab 10- Chemical Dye: An introduction to spectroscopy Introduction: A spectrophotometer is used by selecting a wavelength which changes the intensity of light shone upon a substance and then reports the absorbance of light by that substance. High levels of absorbance (A) mean that the sample absorbed a lot of light and small values of A mean that the sample did not absorb much light at all. The level of absorbance can indicate the particular concentration of a solution. An equation, the Beer-Lambert Law, A = εlc can be used along with the recorded absorbance levels to find the extinction coefficient (ε) which then can be used to calculate unknown concentrations of samples based on their absorbance.

Hypothesis: Chemical dyes can be characterized by calculating their extinction coefficient (ε) and 𝜆max values. Using these values along with the Beer-Lambert Law can allow for the calculation of unknown concentrations of dye. Experimental Methods: Groups used four dye samples: erioglaucine, sunset yellow, fast green, or allura red.The dye in each stock solution was at a concentration of 0.01, but the samples were diluted with deionized water to obtain concentrations of 0.0001M, 0.00001 M, 0.00008 M, 0.00005 M, 0.00003 M for each type of dye. The first experiment was to determine the wavelength at which each dye absorbed the light most strongly. This was done by repeatedly alternating between placing a blank sample of demonized water in a spectrophotometer and zeroing the absorbance, and then placing a 0.00001 M sample of the dye in the spectrophotometer to get a reading at that wavelength. The wavelength started at 400 nm and was increased in increments of 20 nm up to 700 nm. From this, the maximum absorbance of each dye was able to be found. Next, using the wavelength corresponding to the maximum absorbance of each dye, absorbance levels were measured for each dye at all of the varying concentrations.

Finally, each dye was combined with a specified amount of bleach, a 6% solution of sodium hypochlorite. Absorbance of light was measured over a period of 20 minutes for each of these solutions. 0.00001 M Erioglaucine was combined with 10 drops of NaOCl (the bleach), 0.0001 M sunset yellow was combined with 2 drops, 0.0001 M fast green was combined with 1 mL NaOH, and 0.001 M allure red was combined with 1 drop of NaOCl.

Data: Figure 1- Absorbance of dyes at given wavelengths Wavelength

Absorbance of 0.00001 M Erioglaucine

Absorbance of 0.0001 M Sunset Yellow

Absorbance of 0.0001 M Fast Green

Absorbance of 0.0001 M Allura Red

400 nm

0.052 A

0.054 A

0.047 A

0.038 A

420 nm

0.040 A

0.060 A

0.068 A

0.043 A

440 nm

0.016 A

0.073 A

0.054 A

0.051 A

460 nm

0.009 A

0.116 A

0.024 A

0.078 A

480 nm *

0.004 A

0.154 A

0.011 A

0.123 A

500 nm

0.005 A

0.149 A

0.012 A

0.153 A

520 nm

0.015 A

0.093 A

0.021 A

0.145 A

540 nm

0.031 A

0.020 A

0.061 A

0.111 A

560 nm

0.067 A

0.007 A

0.107 A

0.390 A

580 nm

0.138 A

0.005 A

0.202 A

0.006 A

600 nm

0.213 A

0.005 A

0.334 A

0.002 A

620 nm *

0.424 A

0.003 A

0.627 A

0.002 A

640 nm

0.424 A

0.002 A

0.381 A

0.002 A

660 nm

0.110 A

0.002 A

0.074A

0.004 A

680 nm

0.015 A

0.00 A

0.012 A

0.003 A

700 nm

0.003 A

0.00 A

0.002 A

0.002 A

Figure 2- Graph of Absorbance of dyes at given wavelengths

Erioglaucine Sunset Yellow Fast green Allura Red

Figure 3- Absorbance over time for Erioglaucine and Sunset Yellow Time

Absorbance of 0.00001 M Erioglaucine at 620 nm

Absorbance of 0.01 Sunset Yellow at 480 nm

0s

0.085 A

0.720 A

10 s

0.055 A

0.273 A

20 s

0.025 A

0.115 A

30 s

0.012 A

0.042 A

40 s

0.006 A

0.018 A

50 s

0.003 A

0.007 A

60 s

0.002 A

0.003 A

70 s

0.001 A

0.001 A

80 s

0.001 A

0.00 A

90 s

0.001 A

0.00 A

100 s

0.00 A

0.00 A

Figure 4- Absorbance over time for Allura Red and Fast Green Time

Absorbance of 0.00001 M Allura Red at 500 nm

Absorbance of Time (CONT.) 0.00001 M Fast Green at 620 nm

Absorbance of 0.00001 M Allura Red at 500 nm

Absorbance of 0.00001 M Fast Green at 620 nm

0:00

3.015 A

1.520 A

5:30

0.036 A

0.343 A

0:10

3.017 A

1.515 A

6:00

0.034 A

0.320 A

0:20

3.017 A

1.429 A

6:30

0.032 A

0.300 A

0:30

3.016 A

1.347 A

7:00

0.031 A

0.281 A

0:40

3.014 A

1.265 A

7:30

0.030 A

0.264 A

0:50

2.947 A

1.119 A

8:00

0.029 A

0.248 A

1:00

2.857 A

1.126 A

8:30

0.028 A

0.233 A

1:10

2.405 A

1.070 A

9:00

0.027 A

0.219 A

1:20

1.857 A

1.015 A

9:30

0.026 A

0.206 A

1:30

1.381 A

0.962 A

10:00

0.025 A

0.193 A

1:40

0.947 A

0.904 A

10:30

0.024 A

0.181 A

1:50

0.670 A

0.890 A

11:00

0.024 A

0.170 A

2:00

0.477 A

0.876 A

11:30

0.023 A

0.159 A

2:10

0.329 A

0.828 A

12:00

0.022 A

0.149 A

2:20

0.231 A

0.788 A

12:30

0.022 A

0.130 A

2:30

0.161 A

0.750 A

13:00

0.022 A

0.121 A

2:40

0.117 A

0.718 A

13:30

0.021 A

0.119 A

2:50

0.086 A

0.687 A

14:00

0.021 A

0.112 A

3:00

0.068 A

0.659 A

14:30

0.021 A

0.110 A

3:10

0.057 A

0.580 A

15:00

0.020 A

0.108 A

3:20

0.051 A

0.560 A

15:30

0.020 A

3:30

0.047 A

0.541 A

16:00

0.020 A

3:40

0.045 A

0.522 A

16:30

0.020 A

3:50

0.044 A

0.504 A

17:00

0.019 A

4:00

0.042 A

0.488 A

17:30

0.019 A

4:10

0.041 A

0.473 A

18:00

0.019 A

4:20

0.040 A

0.458 A

18:30

0.019 A

4:30

0.040 A

0.445 A

19:00

0.019 A

4:40

0.039 A

0.432 A

19:30

0.019 A

4:50

0.038 A

0.397 A

20:00

0.019 A

5:00

0.037 A

0.368 A

Figure 5- Graph of absorbance over time for all 4 dyes

Erioglaucine Sunset Yellow Fast Green Allura Red

Figure 6- Absorbance of all 4 dyes at varying concentrations Concentration of dye

Absorbance of Erioglaucine at 620 nm

Absorbance of Sunset Yellow at 480 nm

Absorbance of Allura Red at 500 nm

Absorbance of Fast Green at 600 nm

0.0001 M

1.772 A

0.162 A

1.409 A

2.792 A

0.00008 M

2.701 A

1.382 A

1.294 A

2.781 A

0.00005 M

0.884 A

0.885 A

0.897 A

2.730 A

0.00003 M

0.785 A

0.563 A

0.477 A

2.024 A

Figure 7- Graph of the absorbance of all 4 dyes at varying concentrations

Erioglaucine Sunset Yellow Allura Red Fast Green

Calculations: Finding the extinction coefficients Erioglaucine: 2.701= ε (1cm)(0.00008 M) ε = 2.701/ (1cm x 0.00008 M) ε = 33,762.5 Sunset Yellow: 1.382= ε (1cm)(0.00008 M) ε = 1.382 / (1cm x 0.00008 M) ε = 17,275 Allura Red: 1.409= ε (1cm)(0.0001 M) ε = 1.409 / (1cm x 0.0001 M) ε = 14,090

Fast Green: 2.792= ε (1cm)(0.0001 M) ε = 2.792 / (1cm x 0.0001 M) ε = 27,920 Data Analysis: There were several errors that could have taken place during this lab and altered the data. First in the dilution of the concentrated samples of dyes, there could have been errors making the resulting samples too dilute, or not dilute enough. This would in turn alter the amount of light absorbed for each concentration. Another error could have come from the spectrophotometers themselves— if there was a substance on the cuvette that blocked light, the spectrophotometers could have mistakenly read the sample as if there was more light absorbed than actually was. For future experiments, it would be most accurate to have students compare the data they found and average it out to minimize the effect of a random error, and students being more cautious in the use and readings of the spectrophotometers.

Conclusion: The experiment was successful in proving the hypothesis to be true— one can characterize a chemical or dye by discovering its extinction coefficient and λmax. Although there was the potential for error, those that may have occurred did not appear to significantly alter the data. For erioglaucine, it was found that it absorbs the most light at a concentration of 0.00008 M and 620 nm. For sunset yellow, it was found that it absorbs the most light at a concentration of 0.00008 M as well and at a wavelength of 420 nm. For fast green, it was found that it absorbs the most light at a concentration of 0.0001 M and at a wavelength of 500 nm. Finally, Allura Red, it absorbed the most light at a concentration of 0.0001 and a wavelength of 600 nm. Overall, fast green seemed to absorb light the best with an optimum absorption of 2.792 A, however erioglaucine had the highest extinction coefficient of 33,792.5....