Reaction of chromium with air

Chromium metal does not react with air or oxygen at room temperature.

Reaction of chromium with water

Chromium metal does not react with water at room temperature.

Reaction of chromium with the halogens

Chromium reacts directly with fluorine, F₂, at 400°C and 200-300 atmospheres to form chromium(VI) fluoride, CrF₆.

Cr(s) + 3F₂(g) CrF₆(s) [yellow]

Under milder conditions, chromium(V) fluoride, CrF₅, is formed.

2Cr(s) + 5F₂(g) 2CrF₅(s) [red]

Under still milder conditions, chromium metal reacts with the halogens fluorine, F₂, chlorine, Cl₂, bromine, Br₂, and iodine, I₂, to form the corresponding trihalides chromium(III) fluoride, CrF₃, chromium(III) chloride, CrCl₃, chromium(III) bromide, CrBr₃, or chromium(III) iodide, CrI₃.

2Cr(s) + 3F₂(g) 2CrF₃(s) [green]

2Cr(s) + 3Cl₂(g) 2CrCl₃(s) [red-violet]

2Cr(s) + 3Br₂(g) 2CrBr₃(s) [very dark green]

2Cr(s) + 3I₂(g) 2CrI₃(s) [very dark green]

Reaction of chromium with acids

Chromium metal dissolves in dilute hydrochloric acid to form solutions containing the aquated Cr(II) ion together with hydrogen gas, H₂. In practice, the Cr(II) is present as the complex ion [Cr(OH₂)₆]²⁺. Similar results are seen for sulphuric acid but pure samples of chromium may be resistant to attack. Chromium metal does not react with nitric acid, HNO₃ and in fact is passivated.

Cr(s) + 2HCl(aq) Cr²⁺(aq) + 2Cl^-(aq) + H₂(g)

Reaction of chromium with bases