Mystery in the Lab: Forensic Chromatography & Poison Analysis

Part 1: Engage (The Case)

Customs agents have intercepted a shipment of “Imported Gummy Bears” (Candy B) suspected of containing Rhodamine B, a toxic, polar fluorescent dye used in industrial coloring but banned in food. As a forensic chemist, your job is to separate the mixture and determine if the $R_f$ value of any component matches the known profile of Rhodamine B.

Initial Investigation:

  1. Look at the Microscopic View in the simulation. What are the grey “fibers” and how do they interact with the colorful dye molecules?
  2. If a molecule is “sticky” and stays at the bottom of the paper, does it have a stronger attraction to the Stationary Phase (the paper) or the Mobile Phase (the solvent)?

Part 2: Explore (Optimizing the Investigation)

Chromatography only works if you choose the right solvent. Test the three available solvents using Candy A (Cosmic Skittles).

Solvent Type Separation Success (Yes/No) Observation (Describe the bands)
Highly Polar (Water)    
Moderately Polar (Isopropyl)    
Non-polar (Hexane)    

Analysis:

  1. Which solvent provided the best separation (the largest gap between colors)?
  2. In Highly Polar (Water), which color had the highest $R_f$ (moved the furthest)?

Part 3: Explain (The Chemistry of Speed)

  1. Intermolecular Forces: Paper is made of cellulose, which is highly polar. Using the Microscopic View, explain why a polar dye (like Rhodamine B) moves differently when using a non-polar solvent vs. a highly polar solvent.
  2. Mathematical Modeling: Calculate the $R_f$ for Red 40 in Water. $R_f = \frac{\text{Distance of Dye}}{\text{Distance of Solvent Front}}$ Show your work using the values from the Experimental Results table.

Part 4: Elaborate/Evaluate (The Verdict)

Objective: Is Candy B Safe?

Run a final investigation on Candy B: Imported Gummy Bears using the Moderately Polar (Isopropyl) solvent.

  1. Collect Data: Record the $R_f$ values for all three bands found in Candy B.
  2. Evidence-Based Verdict: Compare your calculated $R_f$ values to the FDA Reference Database provided in the simulation.
    • Band 1 $R_f$: ___ Identification: ___
    • Band 2 $R_f$: ___ Identification: ___
    • Band 3 $R_f$: ___ Identification: ___
  3. Formal Report: Based on your data, should the shipment of Gummy Bears be seized or sold? Justify your answer by explaining how the electrical forces between the dye molecules and the solvent determined the outcome of your test.