Paraphrasing

The goal of the experiment performed in the lab was to determine the factors that affect the intensity of the color of a solution as measured by a spectrophotometer (colorimeter) and to develop an equation that relates the amount of light transmitted through a solution to the concentration of the solution. For the purposes of this lab, knowledge of certain concepts was necessary. The use of the spectrophotometer (colorimeter) was especially pertinent in the lab because it was the primary tool of use. A spectrophotometer is an instrument that measures the amount of light through a specific wavelength that passes through a medium. The mediums through which the light passed during the lab were capsules or cuvettes with varying concentrations of dye solution. The spectrophotometer measured the percent of transmittance of light through the dye solutions rather than the absorbance of the light through the dye solutions. Partial absorption is also important, which describes the relationship between light and matter, explaining that some colors of light are absorbed by an object while others are transmitted through or reflected by the object. The colors that are not absorbed by an object are the colors that people can see. Thus, the color of a solution is determined by which wavelengths of light (which colors of light) it will absorb and which ones it will transmit or reflect. The solutions used during the experiment where diluted to different concentrations in order to test the percent transmittance through the solution using constant wavelength. Dilution, in this case, is in reference to weakening the dye solution by adding water resulting in a lesser concentration or amount of the dye solution.

Procedure:

Materials:

· Red dye

· Blue dye

· Green dye

· Spectrophotometer (colorimeter)

· Test tube holder

· 5 large test tubes

· 20mL Graduated cylinder

· 2 cuvettes

· Pipette

· Deionized (DI) water

· 10mL 100% concentration red dye solution

· 10mL 80% concentration red dye solution

· 10mL 60% concentration red dye solution

· 10mL 40% concentration red dye solution

· 10mL 20% concentration red dye solution

· 10mL 10% concentration red dye solution

· 10mL 0% concentration red dye solution

Steps:

PART 1

To begin the first part of the lab, all of the necessary materials were acquired. First, one cuvette was filled with DI water and used to calibrate the spectrophotometer. The same cuvette of water would be used between every reading taken with the cuvette filled with a dye solution. The second cuvette was then filled with red dye and placed into the spectrophotometer at 470nm wavelength. The results were then recorded as percent transmittance and the spectrophotometer was recalibrated. The red dye would then be tested twice more with the same process using 565nm wavelength and 635nm wavelength respectively. All three trials done with the red dye would then be performed with the green dye and the blue dye respectively.

PART II

To begin the second part of the lab, the necessary materials were again gathered. First, the spectrophotometer was set at a constant wavelength of 470nm and a cuvette was filled with DI water to calibrate the spectrophotometer initially and between trials with the red dye solution. The 100% concentration red dye solution was then placed in a cuvette and analyzed for percent of transmittance with the spectrophotometer. To create the various concentrations of red dye solution to be analyzed, DI water was used to dilute the 100% concentration red dye. The 80%, 60%, 40%, 20%, and 10% concentrations of red dye solution were made by combining 8mL of red dye and 2mL of DI water, 6mL of red dye and 4mL of DI water, 4mL of red dye and 6mL of DI water, 2mL of red dye and 8mL of DI water, and 1mL of red dye and 9mL of DI water respectively to a 20mL graduated cylinder. Each of the solutions was transferred to a different large test tube and a portion of each of the solutions from the test tubes was then transferred into a cuvette for analysis by the spectrophotometer. Two trials were conducted for each of the concentrations of red dye solution.

Discussion:

It was found in this experiment that the transmittance of light when it was passed through the same dye at 100% concentration was always near 100%. This meant that no matter what concentration dye was used, it was likely that little to no light would be absorbed by the dye. Also, the red and blue dyes at 100% yielded the lowest transmittance numbers when the opposite color was passed through. Given that these two colors are farther apart from each other on the visible light spectrum than they are from green; this means that the farther apart two colors are the greater amount of light will be absorbed. Also as the percent concentration of dye increased, the transmittance of light decreased in all of the experiments conducted except one. The one experiment where this did not occur truly anomalous, it occurred when red light was passed through green dye, and the results did not follow the pattern set by all of the experiments. The reason for the low transmittance numbers could be any number of things, such as contamination of dyes in the corvettes, spilled dye in the colorimeter, or some other factor that would absorb light. However the high transmittance numbers when the dye concentration was at 100% must be due to some operator or mechanical error, given that 100% concentration, transmittance should be relatively low and there is no source that would emit more light into the colorimeter.

References

Bauer, Birk, & Sawyer (2009). Laboratory Inquiry in Chemistry, 3rd Edition. Brooks/Cole.

Brown, LeMay, Bursten, & Murphy (2011). Chemistry, The Central Science, 12th Edition.