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The Breathalyzer Test

Summary

Orange chromic acid reagent is added to two cylinders, one containing water, the other ethanol. The reagent does not react with water and the resulting solution is orange. Ethanol, however, is oxidized to acetic acid, and the orange chromium (VI) is reduced to green chromium (III).

Hazards

  • Chromium compounds are considered carcinogenic: Use care! Wear gloves!
  • Ethanol is flammable.

Chemicals and Solutions

  • Chromic acid reagent
  • 95% Ethanol
  • Water

Materials

  • Two smallish hydrometer cylinders
  • Plastic eyedropper

Procedure

  1. Add ethanol to one cylinder and water to the other.
  2. Add a small amount of chromic acid reagent to each cylinder using a disposable plastic eye dropper.

Discussion

The hydrometer containing water will remain orange (from the chromium (VI) ion).

The hydrometer containing ethanol will turn dark green from the chromium (III) ion).

\(\ce{$\underset{\text{orange}}{\ce{3C2H5OH + 2H+_{(aq)} + Cr2O72-_{(aq)}}}$->$\underset{\text{green}}{\ce{3CH3COOH + 2Cr3+ + 4H2O}}$}\)

Ethanol is oxidized to acetic acid. Chromium (VI) is reduced to chromium (III).

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