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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 (FeSCN
2+), 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 FeSCN
2+ ions. The second set of solutions is then analyzed, and the FeSCN
2+ 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 K
eq for FeSCN2+ Inquiry Guidance and AP
® Chemistry Curriculum Alignment Transition Guide available! Follow the link in Resources to find this valuable publication that lets you adapt this classic AP Chemistry experiment for guided-inquiry and correlate with the AP Chemistry curriculum framework.
XXInquiry Guidance and AP* Chemistry Curriculum Alignment Transition Guide available! Follow the link in Resources to find this valuable publication that lets you adapt this classic AP Chemistry experiment for guided-inquiry and correlate with the AP Chemistry curriculum framework.