It reacts with water to make hydrofluoric acid , oxygen , and cobalt ( II ) fluoride . It is made by reacting cobalt ( II ) chloride and fluorine at 350 C. Cobalt ( II ) oxide and cobalt ( II ) fluoride can be used instead of the cobalt ( II ) chloride . Cobalt ( II ) oxide ( CoO ) and cobalt ( II ) fluoride ( CoF2 ) can also be converted to cobalt ( III ) fluoride using fluorine .