Final answer:
Potassium dichromate (K2Cr2O7) was the oxidizing agent used in older breathalyzer tests to oxidize ethanol into acetic acid, with a color change indicating the presence of alcohol.
Step-by-step explanation:
The oxidizing agent that was used in older versions of the Breathalyzer test is K2Cr2O7 (potassium dichromate). When the potassium dichromate reacts with ethanol during the test, it gets reduced from the orange dichromate to the green chromium sulfate. Simultaneously, ethanol is oxidized to form acetic acid. This redox reaction takes place in an acidic environment provided by sulfuric acid, which also assists in transferring ethanol from the breath to the test solution.
The chemical equation for this redox reaction is as follows:
8 H+ + Cr2O7^2- + 3 C2H5OH → 3 CH3COOH + 2 Cr^3+ + 7 H2O
This reaction is fast and efficient due to the presence of Ag+ ions, which serve as a catalyst, allowing the determination of ethanol content in the suspect's breath by colorimetric analysis.