Absorption Spectrums 9/18/15

Absorption of Copper (II) Nitrate

Absorption of Copper (II) Sulfate

Absorption of Zinc Nitrate

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

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

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

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

Using Beer’s Law

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