2 x 10 4 M KMnO 4 and 25 x 10 4 M KMnO 4 After finding the percent

2 x 10 4 m kmno 4 and 25 x 10 4 m kmno 4 after

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2 x 10 -4 M KMnO 4 , and 2.5 x 10 -4 M KMnO 4 . After finding the percent transmittance of each diluted solution and calculating each solution’s absorbance, it was found that as the concentration of KMnO 4 increased, so did its absorbance ( Table 3 and Figure 3 ). This is because absorbance and concentration are directly proportional which means that the higher the concentration, the higher the absorbance 2 . This relationship between absorption and concentration is also supported by the Beer- Lambert Law which states A = ebc, where A is absorbance, e is the molar absorptivity, and c is the concentration of the compound in solution 2 . After achieving the first goal of learning how the Spec 20 works, the second goal of analyzing the phosphate content of rival cola products was set out. The first step in achieving the second goal was to determine the analytical wavelength of phosphate. To do this, two parts potassium phosphate or KHPO 4 were mixed together with one part ammonium vanadomolybdate (AVM). The KHPO 4 was mixed with AVM because phosphate does not absorb UV or visible light. After transferring the solution to a cuvette, the sample’s percent transmittance was found at different wavelengths ranging from 350 nm to 650 nm with intervals of 20 nm so that its analytical wavelength could be determined. Indicated by Table 4 , the analytical wavelength of potassium phosphate was found to be at 370 nm. As shown by Figure 4 and Figure 5 , the Spec 20 was not reading percent transmittance nor absorbance until it was tested at 370 nm. This is because the visible light spectrum only ranges from about 400 nm to around 800 nm 3 . The analytical wavelength was at 370 nm because purple, which is measured at around 400 nm, is the color of potassium phosphate; therefore, potassium phosphate has the highest absorption rate at around 400 nm (370 nm) ( Figure 4 ). After finding the analytical wavelength of potassium phosphate, a series of dilutions were performed to create four solutions with the following concentrations: .0002 M KHPO 4 , .00016 M KHPO 4 , .00012 M KHPO 4 , and .00008 M KHPO 4 ( Table 5 ). Then, the percent transmittance and absorbance of each diluted solution was found to create the calibration curve shown in Figure 6 which also shows that absorbance and concentration are directly proportional.
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  • Fall '06
  • Rillings
  • Chemistry, Light, Electromagnetic spectrum, Visible spectrum, percent transmittance, analytical wavelength

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