Analysis:

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In junior high school chemistry, we studied atoms, molecules, ions and other particles that make up matter. We know that a single particle is invisible to the naked eye and difficult to weigh. However, substances in the laboratory, whether simple or complex, can be weighed. In production, of course, the amount of substances is larger, often measured in tons. The reaction between substances is not only carried out according to a certain number of atoms, molecules or ions invisible to the naked eye, but actually carried out with measurable substances. Therefore, it is necessary to associate particles with measurable substances.

How to connect? It is the basic unit to establish the quantity of matter, and it is a collection containing the same number of atoms, molecules, ions, etc. Science has established a unit to connect particles with each other. Then, how big a collective should the unit of material quantity be?

In recent years, 12g 12C (that is, 0.0 12kg 12C) has been used to measure collective carbon atoms. 12C is a carbon atom with six protons and six neutrons in the nucleus. The number of carbon atoms contained in 12g 12C is Avon gadeau [1] constant. Avogadro constant is accurately measured by experiments. A very approximate value of 6.02× 1023 is adopted here.

Mole is the unit to express the amount of matter, and each mole of matter contains Avon Gadereau constant particles. Mol is abbreviated as Mo, with the symbol mol. For example:

1 mole of carbon atoms contains 6.02× 1023 carbon atoms,

1 mol hydrogen atom contains 6.02× 1023 hydrogen atoms,

1 mol oxygen molecule contains 6.02× 1023 oxygen molecules,

1 mole of water molecules contains 6.02× 1023 water molecules,

1 mole of carbon dioxide contains 6.02× 1023 carbon dioxide molecules,

1mol hydrogen ions contain 6.02× 1023 hydrogen ions,

1mol hydroxyl ion contains 6.02× 1023 hydroxyl ions.

Avo Gadereau constant is a large value, but it is convenient to use moles as the unit of matter. Because the mass of 1mol 12C is 12g, which is 6.02× 1023 carbon atoms. From this, we can calculate the mass of any atom in 1mol.

The relative atomic weight (atomic weight) of an element ① is based on the mass of 112 of12, and the atomic weights of other elements are compared with it, such as 16 for oxygen,1for hydrogen and 55.85 for iron. The ratio of mass of 1 carbon atom to mass of 1 oxygen atom is 12: 16. The atomic number of 1mol carbon atom and 1mol oxygen atom is the same, which is 6.02× 1023. 1 mol carbon atom is 12g, so 1 mol oxygen atom is 16g. Similarly, the mass of any atom in 1mol is in grams, which is numerically equal to the atomic weight of the atom. From this we can directly infer that:

The atomic weight of hydrogen is 1, 1 mole of hydrogen atom is 1g,

The atomic weight of iron is 55.85, and the mass of 1mol iron atom is 55.85 g.

Since we can calculate the mass of any atom of 1mol, we can also infer that the mass of any molecule of 1mol is in grams, which is numerically equal to the molecular formula of the molecule.

The molecular formula of hydrogen is 2 1 mole, and the mass of hydrogen molecule is 2g.

The molecular weight of oxygen is 32 1 mole, and the molecular weight of oxygen is 32g.

The molecular formula of carbon dioxide is 44 1 mol, and the molecular weight of carbon dioxide is 44g.

The molecular formula of water is 18, and the mass of 1mol water molecule is 18g.

We can also infer the mass of 1mol ion. Because the mass of electrons is too small, the mass of electrons lost or gained can be ignored.

The mass of 1molH+ is 1g,

The mass of 1molOH- is 17g,

The mass of 1 mol Cl- was 35.5 g.

For ionic compounds, we can also infer that the mass of 1molNaCl is 58.5g.

In a word, Moore is like a bridge, connecting a single particle invisible to the naked eye with a large number of particles that can be weighed.

It is very convenient in science and technology to measure the amount of matter in moles. For example, from the ratio of atoms, molecules and other particles between reactants and products in chemical reactions, we can directly know the material ratio between them.

C+O2=CO2

1 mol

Second, about the calculation of molar mass

The mass of a substance 1mol is usually called the molar mass of the substance, and the unit of molar mass is "g/mol" and the symbol is g/mol. The relationship between the mass, molar mass and quantity of a substance can be expressed by the following formula:

[Example1] 90g] How much water does 90g rub?

[Solution] The molecular weight of water is 18, and the molar mass of water is 18g/mol.

A: 90g water is equivalent to 5mol water.

What is the mass of 2.5 moles of copper atom?

[Solution] The atomic weight of copper is 63.5, and the molar mass of copper is 63.5g/mol.

Mass of 2.5 mol of copper = 63.5g/mol× 2.5mol =158.8g.

A: The mass of 2.5 moles of copper atom is equal to 158.8 grams.

[Example 4.9g How many sulfuric acid molecules are contained in sulfuric acid?

[Solution] The dosage of sulfuric acid is 98, and the molar mass of sulfuric acid is 98g/mol.

The molecular number of 4.9g sulfuric acid = 6.02×1023/mol× 0.05mol.

=3.0 1× 1022

Answer: 4.9g sulfuric acid contains 3.0 1× 1022 sulfuric acid molecules.