1. Absorption Spectrums
9/18/15

2. Absorption of Copper (II) Nitrate

3. Absorption of Copper (II) Sulfate

4. Absorption of Zinc Nitrate

5. Review the Absorption Spectrum
What do you notice about NO3-1
High absorbance in Cu(NO3)2, but none in Zn(NO3)2; can’t we conclude that the NO3-1 is not absorbing light
We can therefore conclude that Copper is absorbing all of the light at 635 nm

6. Review the Absorption Spectrum
What do you notice about Cu+2
High absorbance in Cu(NO3)2, but none in Zn(NO3)2; can’t we conclude that the NO3-1 is not absorbing light
We can therefore conclude that Copper is absorbing all of the light at 635 nm
Also note, the amount of absorption is the same for both copper solutions, meaning that if the concentration of ions is equal, so will the absorbance no matter the origin of the ions

7. Connections
Beer-Lambert’s law states the amount of light absorbed, A, is related to the concentration of the Cu+2(aq), c, by the equation A = abc
a is the molar absorptivity constant whose value depends on the wavelength used
b is the thickness of the sample
Using the same cuvettes keeps b the same, but changing wavelength will change a

8. Calculations of Molar Absorptivity
Remember – concentration (0.1 M) and thickness (1 cm) don’t change
Since absorptivity values change, it’s easier to determine the concentration of a chemical species by using only 1 wavelength

9. Using Beer’s Law

10. Using Beer’s Law
Using the absorption of known concentrations, you can plot a best fit line.
By comparing the absorption of the unknown amount of copper from your beaker, you can find the concentration
Knowing the concentration will allow you to calculate the amount of grams of copper present, and then the percentage of copper in the shell casing