Muriatic acid or, as it is better known, hydrochloric acid, is one of the most potent chemicals on the planet. Its chemical structure enables the acid to continue reacting with materials without weakening making the potential damage the chemical can cause should humans be exposed to it, very high. For all its dangers, muriatic acid actually makes an excellent cleaner for some metals including copper, as it is able to remove tarnish and other oxidized portions without destroying the metal altogether.
Copper is often associated with noble metals for its resistance to non-oxidizing acids like muriatic (hydrochloric) acid. Copper is a not a noble metal per se like mercury, sliver, or gold, though it displays some of their properties in that copper will resist the degenerative reactions of muriatic acid in the absence of a catalyst. The catalyst in this case, is oxygen which bonds with copper to form copper oxide. Once bonded, the presence of oxygen enables muriatic acid to attack copper and over time dissolve it.
Cleaning Copper with Muriatic Acid
Muriatic acid may be used to clean copper because of its strong molecular structure and relative resistance to oxidation reduction. The acid is able to react with the oxidized material on the surface of the copper without becoming weaker as a result of the reaction. The result is complete removal of the oxidized material leaving only pure copper which the muriatic acid cannot react with as the oxygen has been used up in the cleaning process.
Compounds Formed with Muriatic Acid
When copper is allowed to react with muriatic acid over time it will form a blue-green colored copper chloride which may then be manipulated to form other copper variants. For example, copper chloride boiled with pure copper undergoes a chemical reaction that unifies the oxidation numbers of both compounds to form white colored copper chloride.