A Kool Reaction from the Fine Print

Food and other consumer products are chemicals, too. Ignoring warnings, implied warnings, or fine-print instructions on consumer product labels may change the products. The Kool-Aid soft drink mix package states "Do not store in a metal container". Why? In this activity, students investigate the reduction of artificial food dyes by citric acid-promoted oxidation of a metal (iron) in the form of fine or coarse steel wool. The artificial red and yellow food dyes present in the beverage contain azo linkages (nitrogen–nitrogen double bonds) that are readily reduced to colorless products under mild reducing conditions. Citric acid, which provides tart flavor in the drink, reacts with iron to create the mild reducing conditions. Comparing the reaction times for equal masses of fine and coarse steel wool allows the faster reaction time of the fine steel wool (with more exposed iron atoms) to be observed.