Tantalum, like titanium and zirconium, belongs to the reactive metals and its properties can be compared to molybdenum and tungsten. Tantalum has an extremely resistant oxide skin of tantalum pentoxide. The properties of this oxide skin are so extremely good that it is sometimes compared to glass. The reason for this is that tantalum pentoxide is extremely difficult to dissolve with all kinds of chemical reagents, which also explains its excellent corrosion resistance. At room temperature tantalum is resistant to almost all chemical acids with the exception of hydrofluoric acid and fuming sulphuric acid. However, its resistance to strong hot alkaline solutions is lower.