what causes the rusting of iron nails

Rusting is the process of corrosion of iron and its alloys, such as steel. The "rust" is actually iron oxide and forms when the iron in the nail reacts with the oxygen in the air or in liquids. The causes of rusting are chemical and involve reactions with water and oxygen. Water can combine with carbon dioxide in the air to form carbonic acid, a weak acid. When this acidic solution reaches iron, two reactions occur. First, the acidified water will dissolve some of the iron by removing electrons. Then, the water will begin to break down into hydrogen and oxygen. Free oxygen reacts with dissolved iron to form iron oxide, and iron oxide is rust. Therefore, the presence of water and oxygen are the main conditions needed for iron nails to rust. Other factors that can affect the rusting process include the presence of salt, which can speed up the process, and the finish of the nail, which can affect the rate of rusting.