ME
Name
Lab partner(s)
Date
GSA’s name
Section
PROCEDURE
The procedure was followed as written.
RESULTS
As depicted in the TABLE 1, the stock dye solutions were prepared using the given procedure and their absorbance was measured through absorbance spectrophotometry. The experimental values of the wavelengths at which maximum absorbance of the stock dye solutions was witnessed, were duly recorded in the TABLE 1. The values of Absorbance for four different dilutions of red color chosen for our experiment were recorded in the TABLE 2.
Table 1: Stock Dye Solution Data
|
Dye solution |
Peak (max) wavelength (nm) |
Absorbance |
|
Red |
513.20 nm |
0.011 |
|
Blue |
629.00 nm |
0.888 |
|
Yellow |
427.80 nm |
0.972 |
Table 2: Beer’s Law Data Table
|
Concentration (M) |
Wavelength(nm) from Table 1 |
Absorbance |
|
0.1 |
629.00 nm |
0.083 |
|
0.2 |
629.00 nm |
0.184 |
|
0.4 |
629.00 nm |
0.372 |
|
0.5 |
629.00 nm |
0.436 |
|
Best-fit line equation |
Y=0.921X-0.010 |
Table 3: Concentration of Extracted Dye
|
Primary color |
Wavelength (nm) from Table 1 |
Absorbance |
Concentration (M) |
|
Red |
629.00 nm |
0.397 |
0.443 M |
|
Secondary color Blue |
Wavelength (nm) from Table 1 |
Absorbance |
Concentration (M) |
|
purple |
blue 629.00 nm |
0.217 |
0.247M |
|
|
purple 513.70 nm |
0.229 |
|
Sample calculations:
For primary color (Red):
From the Beer’s law, we can observe that:
y = mx + intercept
By putting the values for the red dye, the above equation can be written as follows:
0.397= (0.921)x + (-0.0108)
x= 0.4078/0.921
x= 0.443M
Therefore, as calculated from the Beer’s law, the unknown concentration (M) for the red dye is 0.222M.
From the Beer’s law, we can observe that:
y = mx + intercept
By putting the values for the purple dye, the above equation can be written as follows:
Since, x= y-b/m
x= 0.060+0.0307/1.159
x= 0.07826M
Therefore, as calculated from the Beer’s law, the unknown concentration (M) for the purple dye is 0.07826M.
The experimental values of the red and orange colors have been shown in the TABLE 3 given above.
Analysis of results:
The spectrometer was used to analyze the absorbance of light at a specific wavelength by the extracted food dye from Froot Loops. The 3 dyes i.e. red, blue and yellow, were chosen for checking their maximum absorbance using the spectrophotometer. The obtained values of absorbance were used to determine the exact concentration of the color/chemical present in the dyes. These concentration values were obtained using the Beer-Lambert Law, according to which the absorbance of a substance depends on the light path length, molar concentration and molar coefficient. As shown above, the results of Beer’s law for red dye were shown in the form of a linear equation.
By plotting the absorbance of chosen food dye on the y- axis and by plotting the values of concentration on the x-axis, we were able to obtain the linear plot. Using the calibration curve, the relationship between A and c can be determined easily.
For example, the graph below is a calibration curve for red dye in Froot loops. Four dilutions of the red dye solution were prepared, and their absorbance was measured experimentally using a spectrophotometer. As depicted by the graph, the intercept is nearly 0, which confirms the linear relationship between the two variables. Since the concentration is 0, therefore the value of absorbance at intercept is nearly 0. Moreover, the linear relationship has been exhibited by the Beer’s law graph drawn and displayed above. This shows that the values of concentration (M) and absorbance are related linearly to each other, which obeys Beer’s law.
DISCUSSION
1. Did your solutions in Part I obey Beer’s Law? How do you know?
Yes, a direct linear relationship has been exhibited by the Beer’s law graph drawn and displayed above by the solutions in part 1. This shows that the values of concentration (M) and absorbance are related linearly to each other, which obeys Beer’s law. This relationship is in accordance with the Beer’s law.
2. Compare and contrast the features of a primary color spectrum with those of a secondary color spectrum.
The secondary color spectrum exhibits the opposite wavelengths as opposed to the primary color spectrum. This is evident by the fact that the orange appears on one side of the color wheel, whereas red appears on the other side of the color wheel. Moreover, there is a stark difference in the wavelengths of peaks exhibited by both the primary and secondary colors. Orange dye (secondary color dye) shows the wavelength of about 600-640nm, where the Red color (primary color dye) shows the wavelength of 320-350 nm approximately.
3. Without using a spectrometer or any other instrument, how could you estimate the concentration of an unknown dye solution?
Yes, in case there is no option to use any instrument in the lab, then color wheel can be used for the estimation of the approximate concentration of the unknown dye solution. All the primary and secondary colors with their wavelengths are shown on the color wheel, which can help us in the estimation of the concentration of an unknown dye solution.
4. Would you be able to use your Beer’s Law equation to calculate an unknown concentration of another primary color? Justify your answer.
Yes, the unknown concentration of another primary color can be calculated by using the Beer’s Law equation. Since, according to Beer’s law, the Absorbance is given by the equation:
A = e L c
Therefore, in case we have the quantities of A, L and e, it is possible to find out the unknown concentration of another primary color.
REFLECTION
In the experiment discussed above, the stock solutions of the three dyes were prepared by me. The other two members were responsible for checking the absorbance values obtained from the spectrophotometer. A joint effort was made for measuring the experimental values for calculation using Beer’s law and making the graph.
The main limitation faced during the performance of this experiment was the fact that due to the presence of unknown impurities, the absorbance values of the stock dyes and the dilutions fluctuated. Moreover, the temperature could not be kept constant due to the varying environmental conditions which might have affected the absorbance values. However, the major advantage of performing this experiment was the fact that using the Beer’s Law equation, we can calculate an unknown concentration of any unknown dye and identify it as well.