Product Details
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.
Correlation to Next Generation Science Standards (NGSS)†
Science & Engineering Practices
Planning and carrying out investigations
Using mathematics and computational thinking
Analyzing and interpreting data
Disciplinary Core Ideas
HS-PS1.B: Chemical Reactions
Crosscutting Concepts
Systems and system models
Energy and matter
Performance Expectations
HS-PS1-1: Use the periodic table as a model to predict the relative properties of elements based on the patterns of electrons in the outermost energy level of atoms.
HS-PS1-2: Construct and revise an explanation for the outcome of a simple chemical reaction based on the outermost electron states of atoms, trends in the periodic table, and knowledge of the patterns of chemical properties.