Lanthanum: reactions of elements
Reaction of lanthanum with air
Lanthanum metal tarnishes slowly in air and burns readily to form lanthanum (III) oxide, La2O3.
4La + 3O2 → 2La2O3
Reaction of lanthanum with water
The silvery white metal lanthanum is quite electropositive and reacts slowly with cold water and quite quickly with hot water to form lanthanum hydroxide, La(OH)3, and hydrogen gas (H2).
2La(s) + 6H2O(g) → 2La(OH)3(aq) + 3H2(g)
Reaction of lanthanum with the halogens
Lanthanum metal reacts with all the halogens to form lanthanum(III) halides. So, it reacts with fluorine, F2, chlorine, Cl2, bromine, I2, and iodine, I2, to form respectively lanthanum(III) bromide, LaF3, lanthanum(III) chloride, LaCl3, lanthanum(III) bromide, LaBr3, and lanthanum(III) iodide, LaI3.
2La(s) + 3F2(g) → 2LaF3(s)
2La(s) + 3Cl2(g) → 2LaCl3(s)
2La(s) + 3Br2(g) → 2LaBr3(s)
2La(s) + 3I2(g) → 2LaI3(s)
Reaction of lanthanum with acids
Lanthanum metal dissolves readily in dilute sulphuric acid to form solutions containing the aquated La(III) ion together with hydrogen gas, H2. It is quite likely that La3+(aq) exists as largely the complex ion [La(OH2)9]3+
2La(s) + 3H2SO4(aq) → 2La3+(aq) + 3SO42-(aq) + 3H2(g)