Avogadro's law

Avogadro announced the following law:

Equal volumes of different gases under the same conditions (temperature and pressure) contain the same number of molecules.

And now let's figure out what he meant... No one knows how to get 1 liter of clean gas in the XIX century, Avogadro was guided at that moment with his vast experience and knowledge in this field, the declared law was nothing more than a hypothesis. Therefore, the law highlighted in the paragraph above must be remembered as it is.

And in order to understand this law, let's define the terms:

Normal conditions

In chemistry, there is a concept of "normal conditions", this is a very friendly term that means normal temperature and pressure, namely - 0 °C (or 273.15 K) and 1 atm. In chemistry , it is always implied, that the experiment is taking place under normal conditions.

Mole

A mole is 6,022 141 29 (27) · 10²³ elements (atoms, molecules or hamsters - it doesn't matter, it's just a number). Then there will be a reduction of 6,022· 10²³, but you understand what I'm talking about.

Molar mass

The molar mass of a substance is the mass of 6,022·10²³ atoms of a chemical element. That is, the molar mass of helium is the mass of 6,022·10²³ helium atoms. The molar mass of nickel is the mass of 6,022·10²³ nickel atoms. And, attention! The molar mass of a water molecule (H₂O) is equal to the mass of 2× 6,022·10²³ hydrogen atoms plus a mass of 6,022·10²³ oxygen atoms.

Where does the molar mass come from? This is a complex chemical experiment, described in the article about the mole, and to solve the tasks will have enough data from the reference book, for example, the molar mass of chemical elements is indicated in the periodic table.

Gas

Gas molecules consist of one or more atoms. Gases helium, neon, argon, krypton consist of one atom, xenon, radon and ohaneson are elements of the last group of the periodic table. The monatomic nature of such gases follows from the structure electron shells of atoms

Diatomic gases are hydrogen, nitrogen, oxygen, fluorine and chlorine. The molecules of such gases consist of two atoms, that is: H₂, N₂, O₂, F₂, Cl₂

Explanation of Avogadro's law

Under normal conditions:

1 liter of hydrogen weighs 0.09 g - this is the result of the experiment, the molar mass of hydrogen gas is 2 - 1.008 g/mol. 1 liter of oxygen weighs 1.429 g - this is also the result of the experiment, the molar mass of oxygen gas is 32 g/ mol.

2.016/0.09 = 22.4 l/mol
32/1,429 = 22.4 l/mol

You can repeat this experiment at home ;)

Thus, 1 mole of gas under normal conditions occupies a volume of 22.4 liters, from where you can make conclusion: 22.4 liters of gas contains 1 mole of molecules.

Task

What mass will 40 liters of oxygen gas have?

To determine the mass from the volume, you will need to find out the number of gas molecules, then calculate their mass.

22.4 liters of gas contains one mole of molecules, from where:

40/22,4 ≈ 1.79
40 liters of gas contains 1.79 mole molecules

Oxygen is a diatomic gas, which means its formula is O₂, that is, one molecule contains 2 atoms oxygen. Hence:

1.79×2 = 3.58
1.79 mole molecules contain 3.58 mole oxygen atoms.

The periodic table shows the molar mass of oxygen and it is equal to 15.999 g/mol, from where:

15.999 × 3.58 ≈ 57.28 g

Answer: 40 liters of oxygen gas has a mass of 57.28 g