Atoms of elements and molecules of substances have a negligible mass. To study the quantitative relations characteristic of chemical reactions, several physical quantities are used. One of them is the molar mass, which can be calculated for atoms, ions and molecules. One of the most important elements on Earth is oxygen, with its participation many reactions and processes occur. To perform calculations according to the formulas of the compounds, the reaction equations, the molar mass of oxygen is used, which is numerically equal to the relative mass of its atom or molecule.
Oxygen
General information about oxygen (chemical element):
- Latin name - Oxygenium;
- chemical symbol - O;
- located in the upper part of the 16th group (formerly - group VI A) of the periodic table;
- located in the second period immediately after nitrogen, in front of fluorine;
- belongs to the chalcogen family;
- the number of the element in the periodic table and the charge of the nuclei of its atoms is 8.
Oxygen as one of the components of the atmosphere for a long time could not be distinguished in its pure form. Gas was called "life-giving," "elixir of life." The honor of the discovery of oxygen is shared among world-famous scientists: K. Scheele, J. Priestley, A. Lavoisier. The term "oxygen" was proposed by A. Lavoisier, based on the important role of matter, its atoms in the formation of oxides and acids.
How is the molar mass of an element or substance found?
When performing chemical calculations, one needs to know the masses of the atoms and molecules of the substances involved in the reactions. But they are too small, which makes it difficult to use units such as grams and kilograms. A solution was found: other quantities were proposed that facilitate calculations. For example, in chemistry, the relative values of atomic and molecular masses are used. The relative atomic mass (Ar) as a physical quantity was introduced in 1961. Its value is 1/12 of the mass of the carbon atom (isotope 12 C).
To perform calculations using formulas and equations using this and other quantities, you need to remember a few rules:
- The mass of the atom is indicated in the periodic system next to the chemical sign. The molar mass has the same numerical value, but with g / mol units.
- The mass of one mole of substance is determined by the formula of the compound, for which the sum of the molar masses of all particles in the molecule is found.
- If the chemical formula has an index indicating the number of structural units, then it is necessary to multiply the molar mass by this coefficient.
Atomic and molecular mass of oxygen
The mass of the oxygen atom was obtained taking into account the number and distribution of its three natural isotopes: Ar (O) = 15.999 (in a.u.m.). In calculations, this value is usually rounded, it turns 16. For each element its atomic mass is a constant value. From the known mass of atoms of the element with serial number 8, the molar mass of the oxygen element can be found. M (O) = 16. Another dimensionless physical quantity - the molecular mass of oxygen - refers to a simple substance. The mass of the oxygen molecule is calculated by multiplying the mass of the atom by a stoichiometric coefficient in the formula: Mr (O 2 ) = Ar (O) . 2 = 16 . 2 = 32. In practice, there is no need to find out what is the molar mass of oxygen, because its value is numerically equal to the mass of the molecule of the substance, but with a unit of measurement g / mol. For a particular compound, its molecular weight is a constant, and is widely used in calculating the amount and mass of a substance.
Amount of substance
In chemistry, for the convenience of calculations, one of the most important physical quantities is used - the amount of substance. It refers not to mass, but to the number of structural units. The unit of measurement of the amount of substance in the International System (SI) is 1 mol. Knowing that 1 mol includes as many particles as they are contained in 12 g of the 12 C carbon isotope, you can calculate the number of atoms, molecules, ions, electrons contained in a sample of any substance. Another constant value was named after the great Italian scientist Avogadro (denoted by N A ). It characterizes the number of structural particles that a substance contains if its quantity is 1 mol. The numerical value of the Avogadro constant is 6.02 . 10 23 1 / mol. It is this number of atoms (molecules, ions) that has a molar mass. The designation of this physical quantity is M, the unit of measurement is 1 g / mol, the formula for calculation is M = m / n (m is mass (g), n is the amount of substance (mol)).
What is the molar mass of oxygen
In practice, there is no need to use the formula M = m / n to calculate the molar mass of oxygen. When solving problems, it is often necessary to determine what the mass is equal to, or to find the amount of substance. In the first case, the formula m = n is used for calculations . M, in the second - n = m / M. The numerical value of the molar mass of the element coincides with the mass of the atom, and for the substance - the molecule. For example, a mass of 16 g has 1 mol of an oxygen element. M (O 2 ) is the molar mass of the oxygen molecule , which is 32 g / mol.
Molar mass of oxygen equivalent
Equivalent is a value equal to the mass of 1 mole of atoms of any monovalent element. In the general case, it is possible to determine the equivalent mass by dividing the molar mass of atoms of a chemical element by its valency, found by the formula of a particular compound. In most of its compounds, oxygen, as a chalcogen chemical element, is divalent. The molar mass of oxygen can be found from the periodic table, its rounded value is 16. The equivalent mass is 2 times less - 8. In chemistry, the law of equivalents is applied, which states that substances react with each other in quantities equal to their equivalents. When performing the calculations, you can use the molar mass of the oxygen equivalent to determine the mass of the equivalent of the substance for which it is unknown.
Oxygen is one of the most important elements in the earth's crust, it accounts for 46.6% of the mass. A simple compound of the same name is the second most abundant in the Earth’s atmosphere. The content of molecular oxygen in the air is 20.947% by volume. With the participation of the atoms of the element and the molecules of the substance, many reactions and processes occur in engineering, industry, living and non-living nature. It is important to take into account quantitative relations in these processes, which greatly facilitates the use of physical quantities, including the molar mass of oxygen.