EXPERIMENT 3

Amanda Buchanan – September 20, 2015

Chemistry 1212 – Section 50

OBJECTIVES:

The objectives of this experiment are to understand why and how spectroscopy is used to determine the components and concentrations of a solution, describe various types of spectroscopy, describe the visible and ultraviolet regions of the electromagnetic spectrum, define Beer’s law and define the relationship between absorbance and transmittance. Other learning objectives are to create a Beer’s law plot for a series of samples with known concentrations, collect spectrophotomic data from unknown and known FDC blue dye samples, perform serial dilutions, calculate concentrations, perform linear regression and determine the equation of a best fit line.

DISCUSSION/OBSERVATION

A solution is composed of a solute dissolved into a solvent. The most common solvent is water. Determining the components and concentrations of solutes in a solution is carried out through a variety of techniques known as spectroscopy. Spectroscopy is the analysis of spectra, typically light or mass spectra, where the spectrum of a source is used to determine the composition of a substance. There are many different spectroscopic methods including circular dichroism, mass spectrometry, Raman, spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, and ultraviolet-visible spectroscopy. A UV-Vis spectrophotometer measures absorbance, which is related to the transmittance of light through a solution. Absorbance is the measure of light intensity that is absorbed by a sample. A=log Io/I is the calculation. Beer’s law mathematically expresses the relationship between absorbance and sample concentration. Absorbance and concentration are directly are proportional. A Beer’s law plot is a graph showing the linear relationship between absorbance and concentration that can be fit to a straight line from which the concentration of an unknown sample can be calculated. A colorimeter is a type of