When to use 3 valent iron in chemistry and when to use 2 valent

First of all, the +2 valence is called ferrous steel, and the +3 valence is called iron (that is to say, it says that xx ferrous iron is to use +2 valence, and if it is said to be xx iron, it is called +3 valence); In addition, it should be noted that the product produced in the displacement reaction can only be ferrous iron (I don't know why, the teacher said) (for example: Fe+CuSo4=FeSo4+Cu); Finally, it should be noted that iron is burned in oxygen to produce Fe3O4, not iron oxide (which can be seen as a synthesis of iron oxide and ferrous oxide). Of course, it can only be seen, but it is not the same).

In both the electrolytic cell and the galvanic cell, iron becomes +2 valence. Iron reacts with acids other than nitric acid to produce hydrogen at +2 valence, and with nitric acid, regardless of dilute nitric acid or concentrated nitric acid, it is to +3 valence. Iron reacts with very strong oxidants generally to +3 valence, such as Br2, Cl2, (Note:

Iodine elemental iron oxide to +2 valence) acid potassium permanganate ......

The trivalent is the most stable.

The main minerals of iron are hematite (Fe2O3), magnetite (Fe3O4), pyrite (FeS2).

Oxide: Feo, black; Fe2O3, brick red.

hydroxide: Fe(OH)2, white; Fe(OH)3, reddish-brown. Fe(OH)2 is very unstable and easily oxidized, and it is easily oxidized in air.

Salts: Mainly complexes, you don't need to master them.

Fe3+ is a strong oxidizing agent that can oxidize many substances, for example, 2Fe3+ +H2S=2Fe2+ +S+2H+;

2fe3+ +2i-=2fe2+ +i2;

2fe3+ +cu=2fe2+ +cu2+;

That is to say, cry oxidation S2-, iodine ions, Cu.

Fe2- has weak reducibility.

Iron reacts with dilute acid to form Fe2+;

That's pretty much it.

When iron reacts with dilute acid, it produces 2 of iron. Such as:

fe+h2so4=feso4+h2↑

Iron reacts with chlorine to form 3 of iron.

2fe+3cl2=2fecl3

In the compound, the name is so-and-so iron, which is 3 iron, such as ferric chloride, iron oxide is trivalent iron. The name is a certain ferrous iron, such as ferrous chloride and ferrous sulfate are 2-valent iron.

Look and react with the object is not strongly oxidized.

For example, when it reacts with HCl, it is +2, and nitric acid is 3.

Iron reacts with sulfur, dilute hydrochloric acid, dilute sulfuric acid, copper sulfate, iron sulfate, etc. to form divalent iron.

Iron reacts with chlorine, heated concentrated sulfuric acid, nitric acid, bromine, etc. to form ferric iron.

Because Menghui is that the valency of oh in Fe(OH)3 is -1 valence, according to the principle of the algebraic sum of positive and negative valencies in the compound is zero, x+(-1)*3=0

x = +3, i.e., in iron hydroxide, the valency of iron is +3 valence instead of Yuanbi +2 valence.

In ferric tetroxide, the valency of oxygen is 2 valence, according to the positive and negative valency algebra of each element in the compound, the valency of iron is equal to zero is 8 3 valence, but the valency of iron is only 2 valence, 3 valence, and 8 3 valence is exactly between 2 valence and 3 valence, so the valency of trioxide with Mori iron (triferric) has both 2 valence and 3 valence.

If the 2-valent iron is a, then the 3-valent iron is (3 a), (2) a (3) (3) (3 a) 3= 8 3a=1 The valence of iron in iron in ferric tetroxide is two + one of 3 + 2 valence.

When iron encounters strong oxidants, such as chlorine and nitric acid, it generates +3 valence; When iron encounters weak oxidants, such as hydrochloric acid, elemental sulfur, etc., it generates +2 valence. In FeO, FeCl2, FeCo3, Fes, FeSo4 and other substances, iron is +2 valence; In Fe2O3, FeCl3, Fe(OH)3, Fe2(SO4)3, etc., iron is +3 valence.

Iron

Iron is a metallic element with atomic number 26, elemental iron chemical formula: Fe, and an average relative atomic mass of . Pure iron is white or silvery-white with a metallic luster.

Melting point 1538, boiling point 2750, soluble in strong acid and medium strong acid, insoluble in water. Iron has 0, +2, +3, +4, +5 and +6 valences, of which +2 and +3 are more common, and +4, +5 and +6 are rare.

Iron is widely distributed in life, and the content of the crust is second only to oxygen, silicon and aluminum, ranking fourth in the high crust content of the earth. Pure iron is a flexible and malleable silvery-white metal, used to make generators and motors of iron stupid hand cores, iron and its compounds are also used to make magnets, drugs, inks, pigments, abrasives, etc., is one of the so-called "ferrous metals" in the industry (the other two are chromium and manganese) (in fact, pure pig iron is silvery-white, and the iron element is called "black metal with suspicion" because the surface of iron is often covered with a protective film with the main component of black ferric tetroxide). In addition, the human body also contains iron, and +2-valent ferrous ions are an important component of hemoglobin and are used for oxygen transport.