Lead

Lead is a reactive metal, but its reactivity is somewhat inhibited by the formation of an outer skin of protective compounds. For example, when a freshly cut piece of lead metal is exposed to the air, it quickly reacts with oxygen to form a thin outer layer of lead oxide. This outer layer then prevents further reaction between the metal and oxygen and other constituents of the air. A similar phenomenon occurs when lead metal is placed into water. Compounds present in water react with lead to form an outer skin of lead carbonate, lead silicate, or similar compounds that protect the metal from further attack. This property helps to explain the long popularity of lead for the lining of pipes designed to carry many different kinds of liquids.

From its position in a table of electrode potentials, one would expect lead to replace hydrogen from acids. But the difference in electrode potentials between the two elements is so small (0.126 volts), that lead reacts with most acids only very slowly indeed. The element does tend to react with oxygen-containing acids more readily, but only because of oxidation that may take place at the same time.

One application that takes advantage of this property is the use of lead to line containers that hold concentrated sulfuric acid. As long as those containers are kept at temperatures below 140°F (60°C), there is essentially no reaction between the acid and metal lining.

When lead does take part in a chemical reaction, it demonstrates one of two oxidation states, 4+ and 2+. Compounds of the former class are known as lead(IV) or plumbic compounds, while those of the latter class are lead(II) or plumbous compounds. Like aluminum, lead is amphoteric and will react with strong bases. The products of such reactions are known as plumbates and plumbites.