Sort out the knowledge points of chemical redox reaction in high school

1. The basic concept of redox reaction:

Oxidation and reduction reactions: oxidation reactions are characterized by an increase in the valency of an oxidized element, which is essentially a process in which the atoms of the element lose electrons (or deviate from the common electron pairs); The reduction reaction is characterized by a decrease in the valency of the reduced element, which is essentially the process by which the atoms of the element gain electrons (or share electron pair bias).

2. Oxidation products and reduction products: generated by oxidation. Substances are oxidation products, and the substances that are reduced to form are reduction products.

Common oxidants are O2, Cl2, concentrated sulfuric acid, HNo3, KmNO4, FeCl3, etc.; Common reducing agents are active metal element, H2, C, CO, etc.

3. Representation of electron transfer in redox: the direction and number of electron transfer are expressed by using a two-wire bridge or a single-wire bridge, the difference between the two is that the use of a two-wire bridge needs to mark the gains and losses of electrons, while a single-wire bridge does not.

4. The balancing of the redox reaction equation is a difficult point, and most of the problems can be solved by mastering the skills required for the equalization of valence and elevation of valence.

Common test methods

The basic concepts of redox reactions and the representation of electrons gained and lost are often examined in the form of multiple-choice questions and fill-in-the-blank questions. The trim of redox reactions and related calculations are examined in the form of ** questions.

Misunderstanding warning

This is a method to compare the oxidation and reducibility of substances.

According to the chemical equation of the redox reaction: in a redox reaction, oxidation: oxidant" oxidation product; Reducibility:

Reducing agent》 reducing product. According to the order of metal activity: the stronger the metal activity, the stronger its reducibility, that is:

Reducibility: K>Ca>Na>Mg>Al>ZN>Fe>SN>Pb>(H)>Cu>Hg>Ag

The stronger the reducibility of a metal, the less oxidizing the metal ions formed after it loses electrons, i.e.:

Oxidation: K+

Fe3+ can react with copper: 2Fe3++ Cu = 2Fe2++ Cu2+, so oxidation: Fe3+> Cu2+.

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The essence of the reaction is that there is a change in valency, that is, there is a shift and shift in electrons. The half-reaction in which the oxidation number increases, i.e., the electrons are lost, is an oxidation reaction; The oxidation number decreases, and the reaction to obtain electrons is a reduction reaction. Substances with increased valence reduce each other and are oxidized by themselves, so they are called reducing agents, and their products are called oxidation products; Substances with reduced valency oxidize each other and are reduced themselves, so they are called oxidants, and their products are called reducing products.

Namely: reducing agent + oxidizing agent - oxidation product + reducing product.

Generally speaking, the reducing product in the same reaction is weaker than the reducing agent, and the oxidation of the oxidation product is weaker than the oxidant, which is the so-called "strong reducing agent to weak reducing agent, strong oxidant to weak oxidant".

Example: Hydrogen-chlorine compound.

The total reaction formula of the chemical reaction of hydrogen and chlorine is as follows:

h2 + cl2 → 2hcl

We can write it in the form of two and a half reactions:

Oxidation reaction: H2 2H+ +2E-

Reduction reaction: Cl2 + 2E-2Cl-

The total unit quality is 0 price. In the first and a half reactions, hydrogen is oxidized from 0 valence to +1 valence; At the same time, in the second half reaction, the chlorine element is reduced from 0 to 1 valence. (In this paragraph, "valence" refers to the number of oxidations).

Two properties of redox reactions.

Reducibility: The ability to lose electrons.

oxidation; The ability to get electrons.

For example, a substance is very reducible = has a strong ability to lose electrons.

In a reaction, the reducing substance: 1, reducing agent 2, reducing product.

In a reaction, oxidizing substances: 1, oxidant 2, oxidation products leakage.

Metallicity is reductive in nature, and reductivity is more than just the properties of metal.

Non-metallic properties are oxidizing in nature, and oxidation is not only manifested as non-metallic elemental properties.

The more reducible a particle is, the weaker its oxidation; The stronger the oxidizing nature of the particle, the weaker its reducibility is.

That is, in the order table of metal activity, the metal in the front is highly reducible, and the metal ions in the back are strongly oxidized.

For example, in the periodic table, fluorine, the non-metallic element with the strongest non-re-ignition metallic properties, has the strongest oxidizing properties. Conversely, the more metallic the element, the more reducible it is.

In all redox reactions, the reducing properties of the reducing agent and the reducing properties of the reduction products.

In all redox reactions, the oxidation of oxidants and the oxidation of oxidation products.

The strength of the reductivity is only related to the difficulty of losing electrons, not the number of lost electrons.

The electrons obtained by the metal do not necessarily change to 0 valence Example: 2Fe + Cu = 2Fe2+ + + Cu2+, Fe3+ - Reed coarse Fe2+