#LOGGER PRO ABSORBANCE PRO#
#LOGGER PRO ABSORBANCE PORTABLE#
Ed., 2011 88 (5), 637-639.Vernier Spectrometer Ocean Optics Red Tide Spectrometer Ocean Optics USB4000 VIS-NIR Spectrometer (Order Codes: V-SPEC, SPRT-VIS, SP-VIS) The spectrometer is a portable light spectrophotometer, combining a spectrometer and a light source/cuvette holder. Klotz, E., Doyle, R., Gross, E., Mattson, B., J. To improve the results, a more sensitive spectrometer and a single cuvette could be used to gain all solution spectra.
#LOGGER PRO ABSORBANCE PLUS#
Error may have also occurred during the spectrum readings since a SpectroVis Plus reader that correlated with Logger Pro 3 was used instead of a more sophisticated UV-Vis spectrometer. This means that the hydronium concentration calculated may be slightly off, thus throwing off the equilibrium value. The calculated value may have disagreed slightly because the calibration curve of the pH meter used was only 90.0. When compared to the literature pK c value of 7.1, the percent difference is 1.4%. To incorporate errors into this calculation:Īccording to the data, the calculated equilibrium constant of the bromothymol blue indicator was (1.2 ± 0.19) M, which translates to a pK c of 7.0 ± 0.2. With these error values, a total standard deviation associated with K c can be calculated. The error in pH values was determined to be ± 0.03 units, and for all absorbance values, there is an error of ± 0.002. Thus, the calculated equilibrium constant for bromothymol blue is 1.12, with a pK c value of 6.95. The calculated K c value can then be converted to a pK c value for better comparison to a literature source (Equation 3).Įquation 2: Determining the equilibrium constantĮquation 3: Determining the pK c value for literature comparison. With these values, the equilibrium constant can be calculated via the equation that adjusts for alternative absorbance values (Equation 2). The concentration of hydronium ions,, is determined from the initial pH reading of the sodium phosphate buffer made (Equation 1).įigure 1: A graph showing the spectra from 375nm to 750nm of each of the different bromothymol blue solutions.įigure 2: A table of absorbance values for each of the 3 bromothymol blue solutions at 453nm and 616nm.Įquation 1: Determining the concentration of hydronium ions.
This gives a more accurate depiction of the calculated equilibrium constant of bromothymol blue.įrom the spectra of each solution (Figure 1), absorbance values at 453nm and 616nm were collected (Figure 2).
However, to account for the fact that multiple species (different colors) of the bromothymol blue that may exist in the solution at one time, the revised equation below subtracts the absorbance of the invading species from the one of interest. After the spectrum of each solution is taken, the following equation can be used to determine the equilibrium constant (K c). This experiment will determine the equilibrium constant of this indicator by comparing the absorbance of a buffer solution containing bromothymol blue at its yellow, blue and green states. When comparing the calculated value to a literature pK c value of 7.1, there is a percent difference of 1.4%.īromothymol blue is a chemical indicator that appears yellow in very acidic conditions, blue in basic conditions, and green in mid pH ranges. After taking the spectra of each the yellow, the blue and the green solutions, a K c value of (1.2 ± 0.19) M and a pK c value of 7.0 ± 0.2 were calculated. By determining the absorbance values of solutions at all of these extremes, the equilibrium constant (K c) of this indicator can be calculated. In acidic solutions, it appears yellow, in basic solutions it is blue, and in mid pH ranges, it is green. Bromothymol blue is an indicator used to detect weak acids and bases.
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