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The Determination of Keq for FeSCN2+—AP* Chemistry Classic Laboratory Kit

By: The Flinn Staff

Item #: AP6352

Price: $25.05

In the Determination of Keq for FeSCN2+ Classic Lab Kit for AP* Chemistry, students find the equilibrium constant for a reaction of iron(III) ions and thiocyanate ions. Students learn of quantitative transfer and colorimetric determination.

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Classic AP Requirement #17—Colorimetric or Spectrophotometric Analysis

In this two-part lab, students will determine the equilibrium constant for the reaction of iron(III) ions with thiocyanate ions (SCN-). In Part 1, a series of reference solutions containing the product ion, iron(III) thiocyanate (FeSCN2+), is prepared. Students then make up test solutions containing a fixed amount of iron(III) ions and different amounts of the SCN- ion. These solutions are analyzed in Part 2 using a colorimeter. The first set of solutions is used to generate a calibration curve of absorbance versus the concentration of FeSCN2+ ions. The second set of solutions is then analyzed and the FeSCN2+ ion concentration of each solution is determined. The students use the data to calculate the equilibrium constant for the reaction of iron(III) ions with thiocyanate ions (SCN-). Students gain valuable experience in the techniques of quantitative transfer, along with the process of colorimetric determination.

Complete for 24 students working in pairs.

Determine Keq for FeSCN2+ Inquiry Guidance and AP* Chemistry Curriculum Alignment Transition Guide available! Adapt this classic AP Chemistry experiment for guided-inquiry and correlate with the AP Chemistry curriculum framework with the Flinn Scientific Inquiry Guidance and AP* Chemistry Curriculum Alignment Guide. Follow the link in Resources to find this valuable publication!


Materials Included in Kit (for 24 students working in pairs): Iron(III) nitrate, potassium thiocyanate.
Additional Materials Required (for each lab group): Beakers or large test tubes, buret or volumetric pipet (shared), colorimeter sensors with computer interface system and data collection software (or spectrophotometers to share), cuvets with lids, labeling or marking pens, pipet bulb or pipet filler, serological pipets, stirring rod, thermometer, lint-free tissues or lens paper, volumetric pipet (shared), wash bottle with distilled or deionized water.

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