ANDREW LAMBERT PHOTOGRAPHY / SCIENCE PHOTO LIBRARY ANDREW LAMBERT PHOTOGRAPHY / SCIENCE PHOTO LIBRARY
Alcohol test. Demonstration of the colour change that accompanies the oxidation of an alcohol by potassium dichromate solution (K2Cr2O7, orange). The dichromate turns green (right) as oxidation of the alcohol (turning it into a carboxylic acid) occurs, along with the reduction of the chromium (Cr). The orange colour is produced by chromium in its +6 oxidation state. The green colour arises as the chromium is reduced to a +3 oxidation state. Here, the alcohol is ethanol (CH3.CH2.OH). This is the alcohol that is found in alcoholic drinks, and this is the test used in some breathalyzers to see if there is ethanol on someone's breath.
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