======Dichromate Breathalyzer======


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**Alternative titles:** The Breathalyzer Test
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====Summary====                   
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====Procedure====  
  - Place two clean, clear cylinders on a tray in a fume hood and label them “water” and “ethanol.”
  - Add a small volume of water to the first cylinder and an equal volume of 95% ethanol to the second.
  - Using a disposable plastic eyedropper, add a small, identical amount of chromic acid or Acidified Dichromate reagent to each cylinder.
  - Gently swirl each cylinder and compare the colors side by side, noting that the water sample remains orange while the ethanol sample turns green.
  - 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.



====Links==== 
WCLN - Breathalyser demo - Chemistry - WCLN: 
{{youtube>9H5BLWf1ob4?}}\\


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


====Variations====
  * 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.



====Safety Precautions====
  * 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.




====Questions to Consider====
 * 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).)