Spectrophotometric Characterization essays

Spectrophotometric Characterization essays In this experiment, there were many goals. The first was to determine the wavelength of maximum absorbance for both the basic and acidic forms of Bromcresol Green (BCG). The second goal was to determine the molar extinction coefficient of BCG. The last goal was to determine the dissociation constant for BCG. Before beginning the experiment, the spectrophotometer needed to be calibrated. Setting the absorbance to 0 when there was nothing (only air) in the machine did this. The first step was to produce an absorption spectra of the acidic BCG and the basic BCG over the range of 340-700 nm. D.D.I H2O was used as the blank. The wavelength of maximum absorbance for the acidic form of BCG was 442.5 nm. The wavelength of maximum absorbance for the basic form of BCG was 616.0 nm. The isobestic wavelength was approximately 410 nm. The next step was to prepare 7 different concentrations of the basic BCG. The maximum absorbencies were recorded for each of the different concentrati ons. These absorbencies were plotted along with the concentrations. The molar extinction coefficient of the basic form of BCG was found to be 3.60x10^4. Beers Law was observed because a linear absorbance-concentration relationship was shown on the graph. The last step required different solutions of BCG, each containing different amounts of acid and base. The absorbencies were taken for these solutions. The dissociation constant for BCG was then found to be 1.80x10^-5 M. This experiment was successful. The dissociation constant was found and was close to the average values for the entire class. Within the science of spectrophotometry, there are many important principles. One of them, Beers Law, says that the amount of light absorbed is proportional to the amount of absorbing substance that the light must pass through. In other words, the molar concentration of a solution is directly proportional to the absorption of the solution (S...