Middle School Chemistry 8th Grade Test Center 50

In a chemical reaction, the sum of the masses of the substances before participating in the reaction is equal to the sum of the masses of the substances produced after the reaction. This law is called the law of conservation of mass. It is one of the fundamental laws that are prevalent in nature.

In any system that is isolated from its surroundings, the total mass remains the same, regardless of the changes or processes that occur. In other words, any change, including chemical and nuclear reactions, does not eliminate matter, but only changes the original form or structure of matter.

The gases that make up the atmosphere around the Earth. Colorless, odorless, the main components are nitrogen and oxygen, as well as a very small amount of radon, helium, neon, argon, krypton, xenon and other rare gases and water vapor, carbon dioxide and dust.

The normal composition of the Earth's air by volume fraction is: nitrogen 78 08 , oxygen 20 95 , argon 0 93, carbon dioxide 0 03, and trace amounts of noble gases such as helium, neon, krypton, xenon, etc. Ozone, nitrogen oxides, nitrogen dioxide.

Oxygen is a chemical element with an atomic number of 8 and is denoted by the symbol "O". In the periodic table, oxygen is a member of the oxygen group of elements, and it is also a highly reactive phase 2 non-metallic element that readily forms compounds (mainly oxides) with almost all other elements. Under standard conditions, two oxygen atoms combine to form oxygen, which is a colorless, odorless, and tasteless diatomic gas with the chemical formula O2.

Reaction with white phosphorus: P4 + 5O2 = 2P2O5, white phosphorus spontaneously combustifies in the air, emits light and heats, and generates white smoke.

Reaction with hydrogen: 2H2 + O2 = 2H2O (condition: ignition) produces a light blue flame that emits a large amount of heat and water is generated.

1.Heating potassium permanganate, the chemical formula is: 2kmNO4===( )K2mNO4+MNO2+O2

2.Potassium chlorate was heated with catalyst MNO2 with the chemical formula: 2kClO3===( , mNO2) 2kCl+3O2

3.Hydrogen peroxide (hydrogen peroxide) in the catalyst MNO2 (or red brick powder, potato, cement, rust, etc.), to produce O2 and H2O, the chemical formula is: 2H2O2===(Mno2) 2H2O+O2

Atoms refer to the basic particles of chemical reactions, and atoms are inseparable in chemical reactions. The atomic diameter is on the order of 10 -10m. Atoms have very small masses and are concentrated in the nucleus.

Electrons determine the chemical properties of an element.

Read it carefully for yourself, and read one chapter a day. It's okay to stick to it. The practice questions are mainly done at the back of the text, and don't read them outside of the classroom. Wait until you are basically proficient to do the exercises in the exercise book.

You can go to the school to find a teacher and ask the teacher to tell you the key points, or look for ** from the Internet yourself, if you don't understand, ask your classmates and teachers, you can go to Jinghan's huaxuefudao online to find the information you want.

Chemistry books have experiments on oxygen production, which are very important, and they need to be looked at closely.

Read well, it's good for you.

Some of the answers to the short-answer questions are in the book.

From the composition of the elements in the earth's crust, it can be compiled into a smooth slip, so that it is easier to remember: raise (oxygen) boudoir (silicon) female (aluminum) upside down (iron) how should (calcium), which (sodium) family (potassium) is not (magnesium) please (hydrogen) wife (titanium)! It is oxysilicon, aluminum, iron, calcium, sodium, potassium, magnesium, hydrogen and titanium!

The recognition of element symbols can also be made into a smooth mouth:

Hydrogen, nitrogen, oxygen, fluorine, helium, neon, argon, carbon, chloride, manganese, barium, sulfur, silicon, phosphorus!

Potassium, calcium, sodium, magnesium, aluminum, zinc, iron, tin, lead, copper, mercury, silver, platinum!

There are also experiments to collect oxygen:

Potassium manganese chlorate dioxide, mix evenly and add heat!

Potassium permanganate also makes it, and the mouth of the test tube should be blocked with cotton!

Two methods of collecting oxygen, draining downward exhaust method!

Fill up the oxygen cylinder and stand upright, move the catheter light first and then turn it off!

The third year of junior high school exams is generally not too difficult, the last semester is mainly the basic equations in the books, memorize the equations well, and it is best to memorize the valence, so as to prevent some unseen equations.

In the third year of junior high school, there will also be a test to distinguish compounds, mixtures, elemental substances, etc., which is easy to judge if there is a definition, and the general body type is also a multiple-choice question.

Take a look at it a little and note the distinction between chemical and physical changes.

There are also some contents of the common examination are some experimental steps, pay attention, junior high school is only a few experiments, especially pay attention to carbon dioxide, oxygen, limestone calcination, clarified lime water, ironmaking, and that's it, you can find some specific topics to do by yourself, so that you can get started more during the exam.

There is also a general rule of law about microscopic, there will generally be a choice of extranuclear electron configuration, it is best to memorize the first 20 elements in the atomic number table, and be able to apply flexibly.

In the first half of the third semester of junior high school, the focus is generally on equations (understanding displacement reactions, redox reactions, etc.), and most of the experimental questions are equations.

The most difficult thing for junior high school students is the inference problem, but this is almost as long as you memorize the equations.

Calculate the type, some equations, just list the formulas, and half the points will be in hand.

That's how I learned chemistry in junior high school, and it was easy to learn. That's how the high school entrance examination is written.

Unit 1, "Into the World of Chemistry", is mainly to master the basic knowledge;

Unit 2, "The Air Around Us", grasps the main characteristics and characteristics of oxygen, nitrogen and hydrogen;

Unit 3, "Water in Nature", grasps the characteristics and decomposition of water;

Unit 4, "The Mystery of the Composition of Matter", grasps the basic concepts of molecules, atoms, ions, electrons, etc.

Students, take your chemistry book, look at the table of contents, and think about how much energy your teacher spends on lecturing. In fact, junior high school chemistry is very simple, remember that chemistry reflects the characteristics of the equation and their products (whether there is any color, whether it is bubbling, whether there is precipitation); the color of the metal ions; It's okay to make a recipe for the reaction equation or something.

Several categories of equations such as oxidation, reduction, decomposition, etc. are more typical.

Chemistry should be able to write element symbols, memorize valency, balance chemical formulas, master the steps and chemical formulas of experimental questions, calculate chemical equations, be proficient in acid-base salt capacity, and be able to fully grasp the solubility table at the end of the next book, so that chemistry will be very simple.

1. The three types of particles that make up matter are molecules, atoms, and ions.

2. The three reducing agents commonly used to reduce copper oxide: hydrogen, carbon monoxide and carbon.

3. Hydrogen as a fuel has three advantages: abundant resources, high calorific value, and the product after combustion is water that does not pollute the environment.

4. There are generally three kinds of particles that make up atoms: protons, neutrons, and electrons.

5. There are only three kinds of ferrous metals: iron, manganese, and chromium.

6. The elements that make up the substance can be divided into three categories, namely: (1) metallic elements, (2) non-metallic elements, and (3) rare gas elements.

7. There are three kinds of iron oxides, and their chemical formulas are (1) FeO, (2) Fe2O3, (3) Fe3O4.

8. The characteristics of the solution are three (1) homogeneity; (2) stability; (3) Mixture.

9. The chemical equation has three meanings: (1) it indicates what substances participate in the reaction and what substances are produced as a result; (2) the ratio of the number of particles of molecules or atoms of reactants and products; (3) Indicates the mass ratio between each reactant and product. There are two principles of chemical equations:

based on objective facts; Follow the law of conservation of mass.

10. Pig iron is generally divided into three types: white iron, gray iron, and ductile iron.

11. Carbon steel can be divided into three types: high-carbon steel, medium-carbon steel, and low-carbon steel.

12. There are three kinds of iron ore commonly used in ironmaking: (1) hematite (the main component is Fe2O3); (2) magnetite (Fe3O4); (3) Siderite (FeCO3).

13. There are three main types of equipment for steelmaking: converter, electric furnace and open-hearth.

14. The three reaction conditions that are often related to temperature are ignition, heating, and high temperature.

15. There are two ways to turn a saturated solution into an unsaturated solution: (1) heating up, (2) adding solvent; There are three ways to turn an unsaturated solution into a saturated solution: cooling, adding solutes, and evaporating the solvent at a constant temperature.

Note: Substances whose solubility decreases with temperature, such as: calcium hydroxide solution changes from saturated solution to unsaturated solution

Cooling, solvent addition; There are three ways to change unsaturated solution to saturated solution: heating up, adding solutes, and evaporating solvents at constant temperature).

16. There are generally three methods of gas collection: drainage method, upward emptying method, and downward emptying method.

17. There are three main causes of water pollution: (1) waste residue, waste gas and waste water in industrial production; (2) Arbitrary discharge of domestic sewage; (3) Pesticides and fertilizers used in agricultural production flow into rivers with rainwater.

18. There are three types of fire extinguishers commonly used: foam fire extinguishers; dry chemical fire extinguishers; Liquid carbon dioxide fire extinguisher.

19. The solubility of solid substances changes with temperature can be divided into three categories: (1) the solubility of most solid substances increases with the increase of temperature; (2) The solubility of a few substances is not affected by temperature very much; (3) The solubility of a very small number of substances decreases with the increase of temperature.

20. There are three reasons why CO2 can extinguish fires: it cannot burn, it cannot support combustion, and it is denser than air.

Stuffy, shouldn't there be all in the book?

I think it's good not to memorize according to the knowledge points, just memorize the knowledge learned in the book, and remember it in connection with related experiments, etc., science and liberal arts are different.