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Tamara Bojanic Chemistry Lab CH227 Lab report #7

Determining the Concentration of a Solution: Beer's Law

Abstract: The task for this lab was to prepare Allura Red standard solutions and using colorimeter to measure the absorbance of each of them. The other task was to find the relationship between absorbance and concentration of a solution and using that relationship to determine the concentration of Allura Red in commercially available beverage (in this case red Gatorade). The result of the experiment showed that the concentration of Allura Red in red Gatorade is 3.88*10^-6 M.

Introduction: The task for this lab was to prepare five solutions of Allura Red with different concentrations. The next step was to determine the concentration of each solution. After that, each standard solution was transferred to a small, rectangular cuvette that is placed into the colorimeter. The amount of light that passes through the solution and strikes the photocell was used to compute the absorbance of each solution. After the absorbance of each solution was known, it was used to make a graph of absorbance vs. concentration. Next step was to find the equation of the graph, namely calibration curve. Calibration curve is a general method for determining the concentration of a substance in an unknown sample by comparing the unkown to a set of standard samples of known concentration. From the graph, the linear realtionship between absorbance and concentration for a solution was determined. That relationship is also known as Beer's law.

Data: Concentration (M)

Absorbance

6.0*10^-6

0.0958161552324

1.0*10^-5

0.150068397374

1.3*10^-5

0.208606600104

1.6*10^-5

0.250680082768

2.0*10^-5

0.328320484486

Results: Volume of Allura Red (mL)

Concentration of Allura red (M)

Volume of the solution Concentration of the (mL) solution (M)

1.

6

1.0*10^-4

100

6.0*10^-6

2.

10

1.0*10^-4

100

1.0*10^-5

3.

13

1.0*10^-4

100

1.3*10^-5

4.

16

1.0*10^-4

100

1.6*10^-5

5.

20

1.0*10^-4

100

2.0*10^-5

To determine concentration of solutions, formula M1V1 = M2V2 was used: Volume of Allura Red * Concentration of Allura Red = Volume of the solution * Concentration of the solution

Absorbance = m*x + b m = 16630 x – concentration of Allura Red b = -0.009524 Absorbance of red Gatorade is 0.055. So, the concentration of Allura Red is: x = (Absorbance – b) / m = 3.88*10^-6 M Concentration of Allura Red in red Gatorade is: 3.88*10^-6 M.

Discussion: The purpose of this lab was to determine the concentration of Allura Red in commercially available beverage, in this case red Gatorade. In order to do that, five solutions with different concentration of Allura Red were made. After the concentrations were calculated, the next step was to determine the absorbance of each of the solution in order to find linear equation between absorbance and concentration, also known as Beer's law. When the absorbance of red Gatorade was determined, simply by putting it into the equation, the concentration of Allura Red was calculated. Since it is really important to be precise in this experiment, possible sources of errors were in measuring parts of the experiment. If in any of the solutions the volume of the solution was different than it was supposed to be, the results would be wrong. In order to maximize accuracy, changeable optics filters are used in the colorimeter to select the wavelength of light which solution absorbs the most. In this experiment, the colorimeter should be set to a wavelength of 470 nm.

Further questions: 1. How many molecules of Allura Red would you consume if you drank one 20 ounce bottle of Gatorade? Concentration of Allura Red: 0.0001 mol/mL M = 0.0001 mol/mL V = 20 oz = 0.591 L = 591 mL n = M*V = 0.0001 mol/mL * 591 mL = 0.0591 molecules There are 0.0591 molecules of Allura Red in one 20 ounce bottle of Gatorade.

2. What mass of Allura Red you would consume if you drank one 20 ounce bottle of Gatorade? If you value is greater than the mass of one 20 ounce bottle, be sure to recheck your calculations. Molar mass of Allura Red: 496.42 g/mol 0.0591 mol * 496.42 g/mol = 29.34 g There are 29.34 grams of Allura Red in one 20 ounce bottle of Gatorade. Since the mass of one 20 ounce is equal to 567 grams, the calculations are reasonable....