Erbium

Erbium dissolves readily in dilute sulphuric acid, forming Er(III) ions and hydrogen gas, H₂. The solution is yellow and is most likely the complex [Er(H₂O)₉]³⁺.

2 Er(s) + 3 H₂SO₄(aq) 2 Er³⁺(aq) + 3 SO₄²⁻(aq) + 3 H₂(g)

Erbium tarnishes slowly in air, and burns readily, forming erbium(III) oxide, Er₂O₃.

4 Er(s) + 3 O₂(g) 2 Er₂O₃(s)

Erbium reacts with all the halogens, forming the corresponding erbium(III) halides.

2 Er(s) + 3 F₂(g) 2 ErF₃(s) [pink]
2 Er(s) + 3 Cl₂(g) 2 ErCl₃(s) [violet]
2 Er(s) + 3 Br₂(g) 2 ErBr₃(s) [violet]
2 Er(s) + 3 I₂(g) 2 ErI₃(s) [violet]

Erbium reacts slowly with cold water, and quickly with hot water, forming erbium hydroxide, Er(OH)₃, and hydrogen gas (H₂).

2 Er(s) + 6 H₂O(g) 2 Er(OH)₃(aq) + 3 H₂(g)