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Absorbance at 540 nm of Bromocresol Purple Dilution Series test tube concentration of sample (ug/mL) A540...

Absorbance at 540 nm of Bromocresol Purple Dilution Series

test tube concentration of sample (ug/mL) A540 nm BcP dilution
1 0 0 n/a
2 0.9375 0.041 1:16
3 1.875 0.08 1:08
4 3.75 0.155 1:04
5 7.5 0.306 1:02
6 15 0.614 0:00

1. The point 0/0 is an important and valid point on this graph. Why? (Explain)  Explain how a hand-drawn graph and excel graph are similar or different.

2. How is the Beer’s Law equation similar to that of a straight line? Explain each component using the letter of the component and using a set of your experimental values. BCP: 0.015M

3. Evaluate your data using the Beer’s Law equation: use the absorbance reading for the highest concentration of a solution, determine the extinction coefficient for the BCP solution you were given. Do you get the same answer if you make this calculation at another concentration?

4. Select 2 random absorbance readings on your line (that you did not actually measure) and explain two different ways you can use your graph to determine the concentration of BCP (µg/mL) of the unknown solutions that might have the selected absorbance values.  ***Provide the results; what values do you determine to be the concentrations of your 2 random absorbance readings?

5. Explain why we refer to a graph such as the one you just constructed as a “standard      curve” or a “calibration curve.” How would a graph such as this one be useful?

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