Unformatted text preview: KH2PO4 was added to a reagent and the absorbencies were recorded. At the lowest wavelength measured, the absorbency is at its greatest. The greatest measured absorbance of KH2PO4 was at 350 nm and the least absorbance was one of the longest wavelengths, at about 530, 590, and 630nm. These results can be viewed in figure 3 directly underneath. 0.6 Figure 3: Wavelength vs. Absorbance in KH2PO4 Absorbence (AU) 0.5
0.4
0.3
0.2
0.1
0.0
350 370 390 410 430 450 470 490 510 530 550 570 590 610 630 650
Wavelength (nm) 5 After determining the absorbency of various molarities of phosphate we were able to devise a calibration curve by graphing the substances and determining a line of best fit. The absorbance of the 0.00002M solution was slightly less than 1. The absorbency of the 0.00005M solution was 0.1811, the 0.0001M solution was absorbed at 0.3516, and the final solution (0.00015) was absorbed at 0.5272. These results are depicted in figure 4 below. Figure 4: Absorbency vs. Concentration
of KH2PO4
0.6000
y = 3528.2x  0.0009 Absorbance 0.5000
0.4000 0.00015, 0.5272 0.0001, 0.3516 0.3000
0.2000
0.1000
0.0000
0.00001 0.00001 0.00005, 0.1811
0.00002, 0.0655 0.00003 0.00005 0.00007 0.00009
Molarity 0.00011 0.00013 0.00015 To determine the phosphate of colas without knowing the concentration to begin with we had to create a calibration curve of KH2PO4 and define the line of best fit. We then extrapolated the values from this curve to come up with the phosphate values of the three colas. Since the colas were diluted down we had to look up their absorbance then multiply its corresponding molarity by 50. Sam’s Cola had an actual phosphate concentration of
0.001102. Pepsi’s phosphate content is 0.003075, and Dr Peppers at the highest of the three: 0.079081. Table 1: Percent Transmittance and Absorbance for Various Colas and Phosphate Content Actual Concentration Cola Type Molarity %T Absorb (M*50)
0.00002204 Sam’s 96 0.017729
0.001102 0.0000615 Pepsi 76 0.119186 0.003075 0.000158162 Dr Pepper 58 0.236572 0.079081 6 Sample Calculation for Diluting KMnO4 Solution M1*V1 = M2*V2 (0.001M)(2.5mL) = (0.0001M)(X) 0.0025M/mL = 0.0001M*X 0.0025 _ = X → 25mL = X 0.0001M (0.001M)(2.5mL) = (0.0001M)(25mL) Discussion For the first experiment, the three colored solutions and the KMNO4 were measured at various wavelengths to determine the solution’s absorbance. The reason for doing this was to determine the relationship between color and wavelength of absorbance. Various solutions and colors have different absorbencies at various wavelengths....
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 Fall '08
 TAYLOR
 pH

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