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Metal dissolution is a chemical process that occurs when water or strong acids interact with metallic objects. Chemical forces extract metal atoms from the solid, dispersing them into the surrounding solution. The extent of dissolution depends on the specific metal and the reacting acid: reactive metals like lead and iron dissolve readily, whereas noble metals such as platinum and gold resist dissolution.
Physical properties—mass, density, size, ductility, hardness, color—describe an object’s form and behavior. Chemical properties, on the other hand, govern how a substance reacts with others. Key chemical descriptors include electronegativity, pH, and ionization state. Because dissolution hinges on electron transfer between metal atoms and acids, it is fundamentally a chemical property rather than a physical one.
All metals possess an intrinsic “activity” that reflects their tendency to lose electrons. The activity series ranks metals from highly reactive (e.g., sodium, lithium) to inert (e.g., gold). When a metal contacts water or an acid, it donates electrons to hydrogen ions, forming hydrogen gas. The metal atoms, now unbound, migrate into the solution.
Strong acids consist of a proton (H⁺) paired with a conjugate base. Hydrochloric acid (HCl), for instance, dissociates in water to release free hydrogen ions, creating a powerful solvent. It readily dissolves moderately reactive metals like zinc and magnesium, while iron, copper, and other transition metals are more resistant. Nitric acid can dissolve metals that HCl cannot, expanding the range of soluble metals.
Highly reactive metals—sodium, potassium, and the alkali metals—react violently with plain water, liberating hydrogen gas that often ignites and can explode. Because of this extreme reactivity, such metals are stored under mineral oil to prevent accidental exposure to moisture.
Noble metals—including platinum, iridium, gold, and osmium—are notably resistant to attack by conventional acids. However, a mixture of hydrochloric and nitric acids, known as aqua regia, can dissolve gold and, at elevated temperatures, even platinum and osmium, though the process is slower.
