Dichromate Breathalyzer

An orange chromic acid (or Acidified Dichromate) reagent is added to two cylinders, one with water and one with ethanol. The water sample stays orange, while ethanol is oxidized to acetic acid and the chromium(VI) reagent is reduced to green chromium(III).

1. Place two clean, clear cylinders on a tray in a fume hood and label them “water” and “ethanol.”
2. Add a small volume of water to the first cylinder and an equal volume of 95% ethanol to the second.
3. Using a disposable plastic eyedropper, add a small, identical amount of chromic acid or Acidified Dichromate reagent to each cylinder.
4. Gently swirl each cylinder and compare the colors side by side, noting that the water sample remains orange while the ethanol sample turns green.
5. When finished, quench small test volumes by carefully diluting and transferring all chromium-containing liquids to a labeled hazardous waste container. Rinse glassware into the same waste container.

WCLN - Breathalyser demo - Chemistry - WCLN:

📄 The Breathalyzer Test - University of Washington: https://chem.washington.edu/lecture-demos/breathalyzer-test

• Compare primary (ethanol), secondary (isopropanol), and tertiary (tert-butyl alcohol) samples to show that tertiary alcohols give little to no color change.
• Use potassium dichromate in sulfuric acid (Jones reagent) prepared at demonstration scale, following institutional rules for preparation and storage.
• Feed ethanol vapor from a balloon or gas washing bottle into the reagent to mimic older breath tests, keeping volumes very small and contained.
• Run a parallel control with an aldehyde (e.g., acetaldehyde) to show a rapid positive response compared with a ketone that reacts more slowly.

• Perform the entire demonstration in a fume hood; avoid inhalation of vapors and aerosols.
• Wear splash goggles, lab coat, and appropriate chemical-resistant gloves at all times.
• Chromium(VI) compounds are toxic and carcinogenic; minimize quantities, avoid skin contact, and prevent spills and splashes.
• Ethanol is flammable; keep away from flames, hot surfaces, and sparks. Use only small volumes.
• Use only plastic droppers for dispensing chromic acid reagent and dispose of them as hazardous waste after a single use.
• Collect all chromium-containing solutions, rinses, wipes, and disposables in labeled hazardous waste containers; do not pour to drain.
• In case of skin contact with reagent, rinse immediately with copious water and follow institutional first aid procedures.

* What redox changes occur in this reaction? (Ethanol is oxidized to acetic acid; chromium(VI) is reduced to chromium(III).)

• Why does the water cylinder remain orange while the ethanol cylinder turns green? (Water is not oxidized under these conditions, so Cr(VI) stays orange; ethanol is oxidized, reducing Cr(VI) to green Cr(III).)
• Write a balanced ionic equation for the ethanol test. (3 C2H5OH + 2 H+ + Cr2O7^2− → 3 CH3COOH + 2 Cr^3+ + 4 H2O.)
• Predict the outcome with isopropanol and tert-butyl alcohol. (Isopropanol, a secondary alcohol, is oxidized to acetone and should give a positive green response; tert-butyl alcohol, a tertiary alcohol, typically shows little or no reaction under these conditions.)
• Why is acid present in the reagent? (Acid establishes the dichromate equilibrium and provides conditions for the Jones oxidation, enabling efficient electron transfer from the alcohol to Cr(VI).)