Chemical reactions of the 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)

Reaction of lanthanum with bases

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lanthanum atomic number