Iron is a grey, silvery metal. It is magnetic, though different allotropes of iron have different magnetic qualities. Iron is easily found, mined and smelted, which is why it is so useful. Pure iron is soft and very malleable
Iron is reactive. It reacts with most acids like sulfuric acid. It makes ferrous sulfate when reacted with sulfuric acid. This reaction with sulfuric acid is used to clean metal.
Iron reacts with air and water to make rust. When the rust flakes off, more iron is exposed allowing more iron to rust. Eventually, the whole piece of iron is rusted away. Other metals like aluminum do not rust away. Iron can be alloyed with chromium to make stainless steel, which does not rust under most conditions.
Iron powder can react with sulfur to make iron(II) sulfide, a hard black solid. Iron also reacts with the halogens to make iron(III) halides, like iron(III) chloride. Iron reacts with the hydrohalic acids to make iron(II) halides like iron(II) chloride.
Iron makes chemical compounds with other elements. Normally the other element oxidizes iron. Sometimes two electrons are taken and sometimes three. Compounds where iron has two electrons taken are called ferrous compounds. Compounds where iron has three electrons taken are called ferric compounds. Ferrous compounds have iron in its +2 oxidation state. Ferric compounds have iron in its +3 oxidation state. Iron compounds can be black, brown, yellow, green, or purple.
Ferrous compounds are weak reducing agents. Many of them are green or blue. The most common ferrous compound is ferrous sulfate.
Ferric compounds are oxidizing agents. Many of them are brown. The most common ferric compound is ferric oxide, the same thing as rust. One reason why iron rusts is because ferric oxide is an oxidizing agent. It oxidizes iron, rusting it even under paint. That is why if there is a small scratch in the paint, the whole thing can rust.
Compounds in the +2 oxidation state are weak reducing agents. They are normally light colored. They react with oxygen in air. They are also known as ferrous compounds.
- Iron(II) sulfide, a shiny chemical that reacts with acids to release hydrogen sulfide, found in the ground
- Iron(II) sulfate, a blue-green crystalline chemical made by reacting sulfuric acid with steel, used to reduce poisons like chromate in concrete
- Iron(II) chloride, a pale green crystalline chemical made by reacting hydrochloric acid with steel
- Iron(II) hydroxide, a dark green powder made by electrolyzing water with an iron anode, reacts with oxygen and turns brown
- Iron(II) oxide, black, flammable, rare
Mixed oxidation state
These compounds are rare; only one is common. They are found in the ground.
Compounds in the +3 oxidation state are normally brown. They are oxidizing agents. The are corrosive. They are also known as ferric compounds.
- Iron(III) oxide, rust, red-brown, dissolves in acid
- Iron(III) chloride, poisonous and corrosive, dissolves in water to make dark brown acidic solution. Made by reacting iron with hydrochloric acid and an oxidizing agent
- Iron(III) nitrate, light purple, corrosive, used in etching
- Iron(III) sulfate, rare, light brown, dissolves in water. Made by reacting iron with sulfuric acid and an oxidizing agent.