**Summer
Research Program for Science Teachers**

*Jacqueline Kennedy Onassis High School
*

*Summer 2000*

How can we determine the concentration of an unknown
solution?

**Instructional
Objectives:**__ __

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]

b. Students
will be able to use the standard curve they have created to
determine the concentration of an unknown solution.

**Materials:**__
__

TI Graphing Calculator

Vernier Colorimeter

Vernier adapter cable

TI-Graph Link

One cuvette

Five 20 x 150 mm test tubes

Tissues (preferrably lint free)

30 mL of 0.40 M NiSO_{4
}

5 mL of NiSO_{4 } of unknown
concentration

two 10 ml pipets (or graduated cylinders)

pipet pump or pipet bulb

distilled water

test tube rack

two 100mL beakers

stirring rod

**Procedure:**__
__

1.
Using the table below, use the distilled water provided to dilute
the NiSO_{4 } and make 5 solutions with known
concentrations.

Trial Number | 0.40
M NiSO_{4} (mL) |
_{}H_{2}0 (mL) |
Concentration
(M) |

1 | 2 | 8 | 0.08 |

2 | 4 | 6 | 0.16 |

3 | 6 | 4 | 0.24 |

4 | 8 | 2 | 0.32 |

5 | 10 | 0 | 0.40 |

2.
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.

4.
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 Beer’s 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 NiSO_{4} .
Find the absorbance for the unknown solution. Then use your
calculator to interpolate along the regression line on your
Beer’s 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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