The Chemistry of Rust Removal

Earlier this week, I was in the bathroom organizing my cabinet when I realized how rusty everything was. Unfortunately, rust is difficult to prevent in humidity-prone areas like the bathroom, and it certainly doesn't look good. However, we can use chemistry to learn how to deal with rust!

The formation of rust is a simple chemical reaction: Metallic Iron reacts with water and oxygen gas to form Iron (III) Oxide, which is the chemical formula for rust. This is why metal objects that come into contact with water or water vapor often are most prone to rust—in fact, this is why it is important to dry your pots and pans after use so that they don't rust. What's critical to understand about the chemistry of rusting is that it is a redox reaction, meaning that electrons are transferred from one atom to another. In this case, metallic Iron donates 3 electrons to become an Iron (3+) ion in a process called oxidation.

So how can we apply this to rust removal? Well, in order to revert Iron back to its natural state, we have to add electrons to it or reduce it. However, this can be difficult to do at home. As such, we resort to using acids that can dissolve the rust altogether. Common rust-removal paints and solutions contain acids capable of dissolving this oxidized form of Iron—in fact, strong, concentrated acids like hydrochloric acid can even potentially dissolve the pure Iron underneath the rust coating. Thus, it is suggested that dilute or weak acids be used in rust removal.

It is important to note that once iron rusts, it is generally considered irrecoverable. After rust-removal using an acidic solution, the top-most layer has been completely dissolved, not converted back to pure Iron. Thus, it is still in your best interest to try to prevent rusting from occurring in the first place!