Now you try it...
John and Suzy want to measure the strength of various mixtures of red koolaid. After finding the proper wavelength, they run 10, 20, 40, and 80% solutions through a spec, and get the following data:
Then they go to the State Fair and get samples of red koolaid from 3 different vendors. These samples have absorbances of 0.7, 1.5, and 2.6 OD. How strong is each glass of koolaid?
First, what is “e”?
- I need a hint ... : Remember that “e” is the rate at which stuff in the water absorbs light.
- ...another hint ... : Slope = rate, so find the slope of the graph
- ...another hint ... : How much does the absorbance change as you go from 0 to 10% koolaid?
- ...another hint ... : Since Beer's Law says the relationship is DIRECTLY PROPORTIONAL,
then the absorbance will change 1/10 th as much from 0 to 1% as from 0 to 10%.
I think I have the answer: e = 0.03 OD / percent koolaid.
So far, we know that e = 0.03 OD / percent koolaid. Fitting that into our equation, we get
OD = 0.03 c
Now that you have “e”, what are the concentrations of the three koolaid samples
(their OD's were 0.7, 1.5, and 2.6 AU's)
- I need a hint ... : you can write an equation for concentration based on absorbance.
- ...another hint ... : To get the equation for concentration, solve for c...
- ...another hint ... : Solving for c...
OD = e c
c = OD / e
c = OD / 0.03
- ...another hint ... : Use Google as a calculator!
I think I have the answer: 0.7/0.03 = 23%
2.6/0.03 = 87%
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