Muriatic acid is the common name for dilute hydrochloric acid (HCl). Historically, it was the term used before Joseph Louis Gay‑Lussac coined “hydrochloric acid” in the early 19th century. The acid is widely used in steel pickling to remove rust and surface oxidation before the metal is sold.
When applied to corroded steel, two reactions occur:
1. 6 HCl + Fe₂O₃ → 2 FeCl₃ + 3 H₂O – iron(III) chloride dissolves, taking rust with it.
2. Fe + 2 HCl → FeCl₂ + H₂ – iron(II) chloride and hydrogen gas form, which can continue to corrode the metal if the acid is left on the surface.
To maximize rust removal while minimizing further corrosion, use only the amount of acid needed for the first reaction and rinse promptly.
Because muriatic acid is a strong corrosive, wear nitrile gloves, safety goggles, and protective clothing. Always add acid to water, never water to acid, to avoid violent splashing. Keep the area well ventilated and have a neutralizing solution ready.
1. Dilute the store‑bought muriatic acid to a 1:10 ratio (acid to water).
2. Apply the solution to the rusted area with a stiff brush, scrubbing until rust flakes away.
3. Rinse thoroughly with clean water and dry immediately.
4. Neutralize any residual acid by applying a paste of baking soda and water, then rinse again.
Phosphoric acid is milder and is the active ingredient in many commercial rust removers. Its reaction with rust is:
2 H₃PO₄ + Fe₂O₃ → 2 FePO₄ + 3 H₂O – iron(III) phosphate is soluble, so rust dissolves without attacking the base metal.
Because it’s less aggressive, phosphoric acid is easier to handle and can be used on a wider range of metals, including cast iron and stainless steel.
