You will need
  • - the periodic table,
  • calculator.
By definition, the molar mass is the mass of 1 mole of a substance, i.e., one portion of a substance containing 6*10 to the 23rd degree of particles (Avogadro's number). Particles can be atoms, ions or molecules. Molar mass is equal in magnitude to the relative atomic mass of the substance (or its relative molecular mass if the substance has a molecular structure).
Thus, to know the molar mass of the gasthat has atomic structure, it is sufficient to find in the periodic table the relative atomic mass, which is always indicated in the table cell next to the name of the element and rounding it to an integer value. For example, for oxygen On the value of the relative atomic mass of the cell is 15,9994, rounding, will receive a 16 - therefore, the molar mass of oxygen is 16 g/mol.
Consider the case when you want to find the molar mass of a gasthat have a more complex molecular structure.
To do this, determine the chemical formula of gas, which atoms are part of it. For example, the molecule carbon dioxide gas CO2 according to the formula contains one atom of carbon C and two atoms of oxygen O.
Write from the periodic table relative atomic masses of all the chemical elements are included in the formula, and rounded to their nearest integer.In this example, with carbon dioxide has already been found for oxygen On the rounded value is 16; similarly, in the table to find relative atomic mass of carbon equal to 12,011, and rounding it to an integer, we get 12.
Fold now all rounded values of relative atomic masses of elements based on their quantitative ratios in the formula. For carbon dioxide gas it will be:12(one carbon) + 2*16(two atoms of oxygen) = 44Вы will receive a number that represents the relative molecular mass of a substance is numerically equal to the molar mass - this is is the desired value of the molar mass of gas, we need only substitute the correct dimension.Thus, in this example the molar mass of carbon dioxide gas was 44 g/mol.