Spectrophotometric Characterization

A detailed Summary of Spectrophotometric Characterization

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 concentrations. 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. Beer's Law was observed because a linear absorbance-concentration relationship was sho

Part 1: Absorption Spectra of the Acidic and Basic Forms of BCG

B=] / [HB-] = (Amix- AHB-)/ (AB= - Amix)

Sample # at 616.0 nm 0.003% BCG (mL) 0.2M NaOAc (mL) .0.2M HOAc (mL) 0.2M HCl (mL) [BCG] (M) Absorbance reading

Filled two disposable cuvettes with 1ml of 0.003% BCG each.

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Approximate Word count = 1129
Approximate Pages = 5 (250 words per page double spaced)

Category: Science

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