Summer Research Program for Science Teachers
Jacqueline Kennedy Onassis High School
How can we determine the concentration of an unknown
a. Students will create a standard curve, plotting the relationship between the concentration of a solution and the amount of light that it is able to absorb. [Content Standard Unifying Concepts- Change, constancy, and measurement] [9-12 Content Standard B- Properties of matter]
will be able to use the standard curve they have created to
determine the concentration of an unknown solution.
TI Graphing Calculator
Vernier adapter cable
Five 20 x 150 mm test tubes
Tissues (preferrably lint free)
30 mL of 0.40 M NiSO4
5 mL of NiSO4 of unknown
two 10 ml pipets (or graduated cylinders)
pipet pump or pipet bulb
test tube rack
two 100mL beakers
Using the table below, use the distilled water provided to dilute
the NiSO4 and make 5 solutions with known
Calibrate the colorimeter. Prepare a blank by filling a
cuvette ¾ full of distilled water. With the light source
turned off, enter this absorbance value obtained as 0% transmittance.
With the wavelength knob in the Red LED position (635 nm), enter
the absorbance value obtained as 100% transmittance.
3. In this same manner, collect absorbance data for each of the five standard solutions. When the percent transmittance value for each solution is displayed , enter the molar concentration for that solution.
Using your calculator, construct a graph of absorbance vs.
concentration. Then perform a linear regression on your
data. [9-12 Content Standard A- Use mathematics to improve scientific
communication] If the data you have obtained are
consistent with Beers Law (a direct relationship between
absorbance and concentration), the regression line should closely
fit the five data points and should pass through (or near) the
origin of the graph.
5. Obtain about 5 mL of the unknown solution of NiSO4 . Find the absorbance for the unknown solution. Then use your calculator to interpolate along the regression line on your Beers Law curve.
6. Use the TI Graph link cable and
program to transfer the graph of absorbance vs. concentration
(including the interpolated unknown concentration) to a laptop
computer. Print a copy of the graph.
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