Absorbance and Spectrometry

Topics: Spectroscopy, Analytical chemistry, Electromagnetic radiation Pages: 3 (903 words) Published: November 10, 2012
This report investigates the absorbance of methylene blue and carmine red using a spectrophotometer to determine the absorption spectra of both solutions. The concentration of the unknown solution of methylene blue was found to be 1.07 x 10-5 M by using the molar extinction coefficient, with absorption of 0.547. It was also found that the results concluded confirmed beer’s law with an R2 value of 0.9989. Introduction

Spectrophotometry is the quantitative measurement of the absorbance or transmittance properties of an analyte as a function of wavelength.

Beer's law states that the absorbance is directly proportional to the concentration of the analyte. A straight line should be observed on an absorbance vs. concentration graph if the experiment is to confirm to Beer’s law.

[The range of where the maximum peak occurred was identified and analysed in detail using smaller increments to fully establish the wavelength at maximum absorption (methods section)]

The aims of this experiment were to confirm Beer’s law as well as apply the molar extinction coefficient. The molar extinction coefficient was used to predict the concentration of the unknown solution of methylene blue from the collected data that was utilized to plot an absorbance against concentration graph. Spectrophotometry spans a wide range of scientific fields, such as biochemistry, molecular biology, materials science and physics, therefore it is important to familiarise the techniques and uses of the spectrophotometer.

Materials and Methods
The absorbance of methylene blue and carmine red were measured using an Ultrospec 1100 Pro spectrometer. Absorbance of the several diluted methylene blue solutions were recorded at the wavelength at which maximum absorbance occurred using the spectrometer, this data was then used to calculate the concentration of the unknown solution of methylene blue. Results

Figure 1 shows the absorption spectrum of black filled dots; carmine red...
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