Iron(III) chloride is a yellow solid. It dissolves in water to make a colloid of iron(III) oxide, making the water look muddy. When it is dissolved in an acidic solution, it is bright yellow. When it is very concentrated in a solution, it is dark brown. It is corrosive to skin and metals. It reacts with iron to produce iron(II) chloride. It fumes hydrochloric acid in moist air. It is a weak oxidizing agent. It reacts with copper(I) chloride to make copper(II) chloride. It breaks down when heated to make chlorine and iron(II) chloride.