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Calculating the Equilibrium Constant of a FeSCN Complex

Calculating the Equilibrium Constant of a FeSCN Complex


This 4-wavelength Colorimeter measures the amount of light transmitted through a sample at a user-selectable wavelength in order to determine the concentration of a solution.  Features such as automatic sensor identification and one-step calibration make this sensor easy to use.  The colorimeter can be used for colored solutions and provides an alternative to the more expensive UV-Vis instrument.  Unlike the UV-Vis instrument, the colorimeter measures within the visible range of the electromagnetic spectrum.    

In this laboratory experiment, your students will use the Vernier colorimeter to calclulate the equilibrium constant of an FeSCN complex.  The equilibrium concentrations of all reactants and products will be calculated and students will use these values to calculate a Keq for the reaction.  Throughout the analysis, students will be required to make a series of standards and generate a calibration curve.  


    This U-PIK will include enough materials for six student groups.  Suggested group size is 2-3 students.  The U-PIK will include the following:


    • 6 colorimeters 
    • 6 LabQuest 2 interfaces
    • 7 vials of 0.0020 M KSCN solution
    • 7 vials of 0.0020 M Fe(NO3)3 solution
    • 7 vials of 0.200 M Fe(NO3)3 solution
    • 7 vials of 1.0 M HNO3
    • 6 sets of 1-, 2-, 3-, 4-, and 5-mL pipettes
    • 7 sets of plastic cuvettes
    • 7 pipette bulbs
    • 7 50-mL volumetric flasks
    • 21 100-mL beakers
    • 6 boxes of Kimwipes
    • 28 50-mL conical tubes
    • 35 15-mL concial tubes
    • 6 bags of transfer pipettes

    You will be required to provide your own water (distilled or deionized) needed for the experiment.  Tap water is not recommended and could have an impact on the laboratory experiment.    


    The colorimeter can be easily used to support the concept of the visible spectrum and chemical equlibrium.  All solutions will be colored and analyzed in the visible portion of the electromagnetic spectrum.     


    Due to the mathematical concepts presented (slope, linear regression line, and chemical equilibrium), the laboratory should be introduced in a high school science classroom.  It should be suitable for any chemistry or AP chemistry course discussing chemical equilibrium.    


    Time:  Two laboratory periods.  Many instructors allow students to make the standards on one day (and analyze them to obtain an absorbance value) and the samples on a different day.    


    Student Level:  

    ADVANCED (Grades 11-12)

  • Colorimeter User Manual

  • Lab Experiment: Preview Document

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