A few questions about the first few chapters of chemistry in the third year of junior high school

1) It is not that no air can enter at all, but it is necessary to minimize the air ingress and affect the experimental results.

2) Phosphorus pentoxide is a solid. Because of the reaction with oxygen, the oxygen is consumed, the air pressure in the bottle decreases, and the liquid level rises.

3) Decreased, as for how much, that has to be calculated.

5) Reduce. Reactions follow the conservation of mass, and the amount of reaction that decreases is generated accordingly.

1) It is only related to the concentration of oxygen, and the concentration of oxygen in the air is small.

3) Pure matter, and oxygen are allotropic forms.

4) In other words, there is no need to consider the influence of air when analyzing.

Time is limited, ditto, I won't write it.

2 (2) Are you sure mercury burns? I don't remember exactly, but the mercuric oxide is a red powder anyway. However, mercury oxide decomposes when heated, so it is suspected that it cannot be burned in the air.

4) It is only isolated from the outside air, not that there is no air, and the gas exchange with the outside world is not considered. In other words, there is less gas in it than you use, and it will not be replenished, and the gas generated will not run out of the bottle as much as it is generated.

To figure out what those do.

1-c 2-a 3- The flame ignites immediately, and the paraffin under the flame softens The flame gradually grows larger, with occasional black smoke There is a layer of black object under the white porcelain plate (it is carbon, which is produced by incomplete combustion) There is white smoke (it is smoke, the smoke is solid, and it is produced due to the condensation of paraffin vapor) The conclusion is (properties): low melting point, low ignition point, incomplete combustion will produce carbon Basis: The flame ignites immediately, the paraffin under the flame softens, and there is a layer of black object under the white porcelain plate.

4- Flame core, inner flame, outer flame 5-1 3 (one-third) Alcohol lamp, test tube clamp (or iron frame) Bottom Move Direction of someone 6- Fan to the nose with your hand at the mouth of the bottle (can dilute the concentration of gas) 7-b 8-a

[No new matter has been generated].

Option C can only be said to be partially the same, that is, carbon is produced by combustion. A is composed of C elements, but the other elements are not certain. 】

3.[None] [There is white smoke] [There is water mist] [There is black smoke coming out] [None] [The conclusion is that the same kind of object reflects different phenomena under different conditions and at different times] [Observed experimental phenomena and experimental records].

4.[Outer Flame, Inner Flame, Flame Heart].

5.[1 3] [ Alcohol lamp, test tube clamp] [Bottom] [Move] [Person or yourself] 6[Keep waving your hand at the mouth of the test tube, and then sniff the gas around the mouth of the test tube] The value from the bottom is larger than the actual value, and the value from the top is smaller than the actual one

Test tubes are used for reactions and short heating times, flasks and evaporation dishes are liquid

3.The question will not be.,Nonsensical.。。 Here's a question very similar to 4Flame Heart, Inner Flame, Outer Flame.

Warm up the bottom and move people.

6.Fan it slightly with your hand and smell it again.

3.Outline.

4.[Outer Flame, Inner Flame, Flame Heart].

The bottom of the alcohol lamp shakes people.

6.Breathe into the nose.

c a3.Sweat... No.

4. Outer flame, middle flame, inner flame.

5 third, alcohol lamp, bottom, shaking, person.

6 Slowly stir up the air flow with your hands and smell it a little. 7b8a

Beakers cannot heat solids!

Chemical equation.

1. The law of conservation of mass

1. Content: The sum of the masses of the substances participating in the chemical reaction is equal to the sum of the masses of the substances generated after the reaction.

NOTE: The law of conservation of mass only applies to chemical changes, not to physical changes;

The mass of a substance that does not participate in the reaction and the mass of a substance that is not a product cannot be counted in the "sum";

Consider whether a substance in the air participates in the reaction or if a substance (e.g. gas) is missing.

2. Microscopic explanation: before and after the chemical reaction, the type, number and mass of atoms remain unchanged (the "three invariants" of atoms).

3. Before and after the chemical reaction:

1) It must not change.

Macroscopic: the total mass of reactant products remains unchanged; The element type remains the same.

Microscopic: The type, number, and mass of atoms remain unchanged.

2) Be sure to change.

Macro: The type of substance must change.

Microscopic: The type of molecule must change.

3) May change: The total number of molecules may change.

2. Chemical equations.

1. Follow the principle: Abide by the law of conservation of quality based on objective facts.

2. Writing: (Note: A, trim B, condition C, arrow).

3. The meaning is to take 2H2+O2 igniting 2H2O as an example.

Macroscopic significance: Indicates reactants, products, reaction conditions, hydrogen and oxygen to produce water under ignition conditions.

Microscopic significance: Indicates the ratio of the number of molecules (or atoms) between reactants and products.

For every 2 hydrogen molecules combined with 1 oxygen molecule, 2 water molecules are formed (for gases, the ratio of the number of molecules is equal to the ratio of volume).

The ratio of mass between substances (coefficient ratio to molecular mass).

Every 4 parts of hydrogen is completely combined with 32 parts of oxygen to produce 36 parts of water.

4. The information provided by the chemical equation includes:

which substances participate in the reaction (reactants); Under what conditions the reaction takes: what substances (products) are produced by the reaction; the relative number of individual particles participating in the reaction; Conservation of mass before and after reaction, and so on.

5. Calculation using chemical equations.

3. Type of chemical reaction.

1. Four basic types of reactions.

Chemical reaction: A reaction in which two or more substances produce another substance.

Decomposition reaction: A reaction in which two or more other substances are produced from one reactant.

Displacement reaction: A reaction in which one element and one compound react to produce another element and another compound.

Metathesis reaction: A reaction in which two compounds exchange components with each other to form two other compounds.

2. Redox reaction.

Oxidation reaction: A reaction in which a substance gets oxygen.

Reduction reaction: A reaction in which a substance loses oxygen.

Oxidizing agent: A substance that provides oxygen.

Reducing agent: a substance that captures oxygen (common reducing agents: H2, C, CO).

3. Neutralization reaction: the reaction of acid and alkali to produce salt and water.

The teaching materials are different and can't help you.