Experiment 2.doc - EXPERIMENT 2 BEERS LAW ADDITIONAL...

EXPERIMENT 2
BEER’S LAW
ADDITIONAL READING
The concepts in this experiment are discussed below. Read all the background information carefully.
CONTEXT
In experiment 1 you learned how titration can be implemented to determine the concentration of acidic or basic
solutions, provided that one has an appropriate standard and end point indicator. While titration is an essential tool
in your chemistry tool belt, it would not be particularly helpful in determining the concentration of a solution which is
not acidic or basic. It is also likely that, as you pursue independent research in the future, you will have so small an
amount of a precious material (you will have invested a lot in it in terms of either money or time/effort) that you will
not want to compromise the material by adding impurities like indicator, etc. even if it is acidic or basic. It is at
moments like these that spectroscopy (the study of the interaction between light and matter) becomes very
powerful.
In this experiment, you will be studying colored solutions using visible light spectroscopy (colorimetry) that will let
you gain a greater qualitative understanding while doing a quantitative exercise. You will learn about invisible light
spectroscopy like infrared (IR) and ultraviolet (UV) spectroscopy (these are strictly quantitative, as you can’t
“eyeball” transmission of invisible radiation) in greater depth when you study organic, biological, and analytical
chemistry, but they operate on the same fundamental principles.
Like titration, Beer’s Law is not just another box to be checked off on a list and cast off as old science that is no
longer relevant. Every lab doing state-of-the-art research on DNA/RNA research anywhere in the world uses Beer’s
law on a daily basis to determine concentrations of their nucleic acid solutions. It is also a stepping stone to
understanding other interesting chemical behaviors like fluorescence and phosphorescence.
OBJECTIVES
As you will be asked to do some experimental design before the end of the semester, you are encouraged to think
about what each experiment is designed to probe. In addition to (re-)learning lab-related words/phrases like
wavelength , frequency , quantized , photons , absorption , transmission , etc., what concept(s) does this experiment
reinforce? Such reinforcement is the objective of the lab.
SUMMARY
This experiment is divided into three parts to be done in one lab meeting.
Part A: You will prepare a stock solution containing a sample of MiO ® (a liquid water enhancer used to make fruit-
tasting drinks; see ). A spectrophotometer will be used to measure the absorbance
spectrum of the solution from which the wavelength at which it absorbs the maximum amount of light, 
max
, will be
obtained.