Oxidation and Reduction

Electrons will travel

Oxidation and reduction reactions are among the most common and important of all chemical processes. Photosynthesis and respiration, combustion of fuels in automobile engines, and the reactions of metal bridges to acid rain are all the result of the movement of electrons from a source to a destination. Anytime you can move particles from one place to another, there is the potential for useful work as a result. These reactions are the basis for how batteries function and the resulting production of a direct current.

Acids and metals

If you examine a box of cereal, you will observe that it includes a reasonable serving of the recommended daily amount (RDA) of iron. Believe it or not, this iron is almost always in the form of powdered iron filings. A simple experiment is to take a bowl of cereal, pour milk over it (or water), and simply stir it with a white clean, plastic-covered magnet. In about 10 minutes, you will collect a noticeable amount of what looks like cast-iron-skillet filings. Iron is magnetic, so as the cereal softens in the solution, the iron is freed from the cereal matrix and is attracted to the magnet. What happens to that iron when it is dumped into the solution of acid in your stomach?

2Fe (s) + 6HCl (aq) → 2 FeCl₃ (aq) + 3H₂ (g)

Two iron atoms give 3 electrons each to 6 hydrogen atoms, which then share a pair of electrons between them to have a stable configuration similar to helium. A total of 6 electrons were exchanged. The iron atoms that have a +3 charge (because they now have 3 more protons than electrons) are attracted to the three chloride ions that have a -1 charge. The iron is said to be oxidized because it has lost electrons. The chlorine has been reduced because it has gained electrons. All the electrons lost are gained by another substance and the iron in the oxidized form can be picked up by hemoglobin to carry oxygen in the blood. Without this transformation, iron cannot perform that duty.