Seek the knowledge of junior high school chemistry and sort out the key knowledge of junior high sch

1. Chemical change: changes in other substances are generated.

2. Physical change: no change in other substances.

3. Physical properties: properties that do not need to undergo chemical changes to manifest themselves.

Such as: color, state, density, odor, melting point, boiling point, hardness, water solubility, etc.).

4. Chemical properties: the properties of substances in chemical changes.

Such as: flammability, combustibility, oxidation, reduction, acidity and alkalinity, stability, etc.).

5. Pure substance: composed of a substance.

6. Mixture: It is composed of two or more pure substances, and each substance retains the properties of the original late lead.

7. Element: A general term for a class of atoms with the same number of nuclear charges (i.e., the number of protons).

8. Atom: It is the smallest particle in chemical change, and it cannot be divided in chemical change.

The color of the solid

1. Red solid: copper, iron oxide.

2. Green solid: basic copper carbonate.

3. Blue solid: copper hydroxide, copper sulfate crystals.

4. Purple-black solid: potassium permanganate.

5. Light yellow solid: sulfur.

6. Colorless solids: ice, dry ice, diamond.

7. Silver-white solid: silver, iron, magnesium, aluminum, mercury and other metals.

8. Black solid: iron matan powder, charcoal, copper oxide, manganese dioxide, ferric tetroxide, (carbon black, activated carbon).

9. Reddish-brown solid: iron hydroxide.

10. Platinum white solid: sodium chloride, sodium carbonate, sodium hydroxide, calcium hydroxide, calcium carbonate, calcium oxide, copper sulfate, phosphorus pentoxide, magnesium oxide.

Acids are compounds composed of hydrogen and acid groups such as sulfuric acid (H2SO4), hydrochloric acid (HCl), and nitric acid (HNO3).

Alkali is a compound composed of metal elements and hydroxides, such as sodium hydroxide, calcium hydroxide, ammonia (NH3·H2O).

Salt is a compound composed of metallic elements, elements (or ammonium) and acid groups, such as sodium chloride and sodium carbonate.

Aqueous solutions of acids, alkalis, and salts can conduct electricity (reason: dissociate to form free-moving anions and cations when dissolved in water).

1) The higher the position of the metal, the more likely it is to lose electrons and become ions in aqueous solution, and the stronger its activity;

2) The metal in front of hydrogen can replace the hydrogen in the acid, but the metal behind the hydrogen cannot replace the hydrogen in the acid;

3) The metals in front can displace the metals in the back from their salt solution.

The above is the key knowledge of the junior high school chemistry common exam that I have compiled for you.

What are the important knowledge points that must be tested in chemistry in the third year of junior high school, and I will introduce the chemistry knowledge points in detail for you below, I hope it can be helpful to you.

Summary of chemistry knowledge points in the third year of junior high schoolUses of common gases

1) Oxygen: for breathing (e.g. diving, medical emergency).

Support combustion (e.g. fuel combustion, steelmaking, gas welding).

2) Nitrogen: protective gas (chemically inactive), important raw materials (nitric acid, Soyukuan fertilizer), liquid nitrogen freezing.

3) Noble gases (He, Ne, Ar, Kr, XE, etc.): shielding gas, electric light source (light of different colors when energized), laser technology.

Classification of substances

Mixture: Composed of two or more pure substances, each of which retains its original properties.

Pure: Consists of a substance.

Elemental: A pure substance composed of the same elements.

Compounds: Pure substances composed of different elements.

Oxide: A compound made up of two elements, one of which is oxygen.

In junior high school chemistry, you must memorize knowledge pointsBurning conditions: (indispensable).

1) Combustibles (2) Oxygen (or air) (3) The temperature reaches the ignition point.

2. The principle of fire extinguishing: (as long as any one of the combustion conditions is eliminated).

1) Eliminate combustibles (2) Isolate oxygen (or air) (3) Cool down below the ignition point.

Determination of oxygen content in air

a. Combustible requirements: sufficient amount and the product is solid.

b. Device requirements: good air tightness.

c. Phenomenon: A large amount of white smoke is generated, and the liquid level in the jar rises by about 1 5 volume.

d. Conclusion: Air is a mixture; O2 accounts for about 1 5 and can support combustion; N2 accounts for about 4 5, does not support combustion, cannot be burned, and is insoluble in water.

e、**: The liquid level rises less than 1 5 Reasons: The device is leaking, the amount of red phosphorus is insufficient, and the spring clamp is opened before it is cooled to room temperature.

What are the answering skills for non-multiple-choice questions in chemistry in the high school entrance examinationAround the core issues

When reviewing chemistry questions in the high school entrance examination, it is necessary to clarify the design of the test questions, find out the direction of the answers, and organize the answers around the core of the questions. For example, experimental design questions, experimental questions, and even comprehensive calculation questions all involve the purpose of the experiment or the purpose, everything you do must serve the purpose of the experiment or the purpose, and do not deviate from the core.

Answer in the most common way

There is no only answer to the open test questions, and the most appropriate answer should be chosen when answering the chemistry questions in the high school entrance examination, and it is not easy to lose points by answering in the most common way. If you can answer with a specific substance, you should use a specific substance, so that the expression is more accurate. You should try your best to write the answers that you are most sure of, have no controversy, and can be recognized by everyone, and do not give others the opportunity to deduct points.