Report Lab 8: Standard Curves and Volumetric Glassware Chemistry 1 Teddy Portney June 25, 2007 Summer 1, 2007
1. Purpose: The purpose of this experiment was to practice using different glassware, as well as refresh our memory as to the production of different concentrations of solutions. We also created a standard curve to aid in the conversion between concentration of solutions and the absorbance of light of the solutions.
2. Experimental Methods: The procedure was followed as described in the handout from Chemistry 1, Summer 2007 at Tufts University for experiment 8; Standard Curves and Volumetric Glassware.
3. Data and Observations: For this lab, we made a table of absorbance versus concentration for six samples of diluted food dye, each with different concentration. Plotting these six data points on a graph, we create a standard curve, with which we can find the concentration of some unknown samples. Here is a table of our samples for the Red #40 dye, as well as the corresponding standard curve.
Sample # Concentration (mg/L) Absorbance at 500nm 0 0 0 1 2 0.044 2 5 0.181 3 10 0.384 4 15 0.585 5 20 0.803
When we took the unknown samples of Kool-aid and Gatorade, the absorbances of 500 nm light by the red dye were too high for our standard curve, so we diluted them. The Gatorade, originally with an absorbance of 1.573, was diluted to , making the new sample's absorbance 0.695. Then, the Kool-aid, originally 1.564, was diluted to 1/5, making the new absorbance 0.612.
4. Results and calculations: Results for parts 1-4 are reported in the data section above. Part 5 asks us to analyze the two commercial beverages by determining concentrations the of Red #40 dye. Using the equation displayed on the graph above, we can convert the known absorbencies into concentrations. These values come out to be 17.08 mg/L for the diluted Gatorade, and 15.16 mg/L for the diluted Kool-aid. Multiplying these values by the inverse of the dilution ratio (1/4 for Gatorade and 1/5 for Kool-aid), we get that the concentrations for the actual undiluted beverages are 68 mg/L for Gatorade and 75.75 mg/L Kool-aid.
5. Discussion and Conclusion: These results make sense, as these commercial beverages rely heavily on food coloring dyes. Looking at the full 20 fluid ounce bottle of Gatorade, the red color overpowers any other ingredients. The dye in these drinks is so concentrated that many tend to stain the tongues and teeth of the people who drink them. This lab could have been better if the results were more accurate. When making solutions, it would have been better if we had prepared one liter of solutions, as opposed to the 100 mL asked for in this lab. This is because one drop of food dye in approximately one liter of water doesn't make as much of an impact as it did in 100 mL.
6. Questions: 1.) The importance of the water-blank sample is that when the sample is put in the absorbency reader, it is possible that the absorbency reads a non-zero number. This would be because the water we used was impure or the container was dirty. 2.) When preparing the standard curve, the concentration was the independent variable, because no matter what the absorbency came out to be, we knew the concentration of a certain sample. This makes the absorbency the dependent variable.