1. Spectroscopy and Beer’s Law
Unit 2
Spectroscopy and Beer’s Law

2. This is a spectrophotometer.
Spec-20D+

3. Spectrophotometers work similarly to this device.
Vernier Colorimeter

4. The spectrophotometer is meant to measure the absorbance of light in a sample.

5. What is absorbance?
A measure of how much light (or electromagnetic radiation) does NOT go through the sample.
This means the sample is typically colored.

6. In the case of the Spec-20D+, or a colorimeter, the portion of the electromagnetic spectrum must be…

7. the visible light wavelengths.
400 nm
700 nm
the visible light wavelengths.

8. So, what is Beer’s Law?
a measurement of the amount of absorption at the wavelength of greatest absorption can determine the concentration of the absorbing species present
A = d c
A = Absorbance
= characteristic absorptivity of the strength of the species
d = thickness of the sample
c = concentration
Create a single number that is constant, k.

9. So, what is Beer’s Law? A = k c
This shows that absorbance (A) is directly proportional to concentration (c).
This relationship will allow you to measure the absorbance of known concentrations and plot them.
You will then measure the absorbance of an unknown concentration. Your graph will allow to interpolate that absorbance to determine the sample’s concentration.
Absorbance
Concentration