Calculate the molar mass of P2O5.

Molecular weight is designated bMr, measured in g / mol (gram per mole)
In order to calculate the molecular weight of the compound, let’s turn to the translation system. Near each element in the table there is a number with a comma – the atomic mass of the element. (The atomic mass of all elements, except for chlorine, is rounded to the nearest whole number (atomic mass of chlorine = 35.5 g / mol.)
Molecular mass of a substance = the sum of the atomic masses of all the elements that make up the substance.
Mr (P2O5) = 31 * 2 (since two phosphorus atoms) + 16 * 5 (since 5 oxygen atoms) = 142 g / mol