Vinegar, a dilute acetic acid solution, can dissolve some metals, especially those high on the reactivity series, but many metals resist it or develop protective layers.
What makes vinegar reactive
Household vinegar contains about 5% acetic acid, a weak organic acid that releases hydrogen ions in water. These protons enable vinegar to attack metal oxides and tarnishes, turning them into soluble salts.
Metals that dissolve in vinegar
- Zinc – reacts quickly, forming zinc acetate and hydrogen gas.
- Iron and steel – vinegar removes rust (Fe₂O₃) and can eventually eat the underlying metal if left too long.
- Aluminum – normally protected by a thin oxide film, but concentrated vinegar can attack it, especially if the film is damaged.
Metals that resist or form protective layers
- Copper, brass, bronze – vinegar dissolves surface oxides to copper acetate, leaving a green patina rather than fully dissolving the metal.
- Silver, gold, platinum – noble metals stay largely unchanged; any reaction is negligible.
- Nickel, tin – form thin, protective oxides that slow further corrosion.
Practical uses of vinegar on metal
- Rust removal – soak rusty iron or steel for 24–48 hours, then scrub; the acid dissolves the iron oxide layer.
- Cleaning tarnish – vinegar removes copper oxide from pennies or brass items, revealing a bright surface.
- Testing metal reactivity – a drop of vinegar on a piece of metal can show whether it reacts (bubble of hydrogen gas).
When vinegar should not be used
Do not leave iron or steel submerged in vinegar for extended periods, as the acid will eventually dissolve the base metal. Avoid using vinegar on delicate alloys or jewelry that may contain precious metals; the acid can weaken or discolor them.
Safety tips
- Wear gloves and eye protection when handling vinegar with metal objects.
- Ventilate the area, as hydrogen gas can build up during reactions.
- Rinse metal thoroughly after treatment to stop further corrosion.