Molar Extinction Coefficient Lab Report

Determining the Absorbance Maximum Wavelength and Molar Extinction Coefficient to Find the Molarity of the Unknown DCPIP
Background Information:
A spectrophotometer is an instrument used to help determine the absorption spectrum of chemicals. It does this by reading the absorbance of the chemical at different wavelengths. All chemicals absorb light in their own distinct way. This distinction helps to identify unknown chemicals. The absorption of light within a chemical is also very important because that amount of light is used to perform work within its system. To help find the absorption of a chemical, the Beer-Lambert law is used. The law states that A=e × c × l; A standing for absorbance, e for the molar extinction coefficient, c for concentration,
To calculate its concentration, we measured its absorbance at 610nm in the spectrophotometer. When we obtained its absorbance, we used the Beer-Lambert law to help calculate the concentration and we rearranged the equation to:
C=A/(e×l)
Results:
The data from determining the absorption spectrum is illustrated in figure 1. The graph shows that it increases up to the absorption maximum, which came out to be at 3.318 at 610 nm, then decreases, creating a curve on the graph. The maximum wavelength was then used to find standard curve which shows the absorbance levels of various concentrations of DCPIP. That data is shown in figure 2. It can be seen that as concentration increases, so does absorbance. Excel traced a line of best fit on the standard curve and the slope of the line was used as the molar extinction coefficient. Now that the absorbance maximum and the molar extinction coefficient are found, they can be plugged into the Beer-Lambert law to find the concentration of unknown
In other words, the higher the concentration, the higher the absorbance. This relationship was shown on the standard curve in figure 2. The Beer-Lambert law was also shown to help us find the concentration of our unknown. We first had to find the absorbance maximum, which ended up being 3.318 at 610 nm. After obtaining that data, we used the wavelength to create the standard curve alongside the absorbance values of several different concentrations of DCPIP. A line of best fit was traced on the standard curve and the slope was used as our molar extinction coefficient (e). After finding our e, we also used our absorbance maximum and the measure of our path length to find the concentration of the unknown by plugging it into the Beer-Lambert