Mole
All substances consist of atoms or molecules. In chemistry, it is important to measure their amounts accurately. The mole is used to express the amounts of reactants and products of chemical reactions. The mole, symbol mol, is the SI unit of the amount of substance. One mole contains exactly 6.02214076×10²³ elementary entities. This number is the fixed numerical value of the Avogadro constant, NA, when expressed in the unit mol⁻¹ and is called the Avogadro number. The amount of substance, symbol n, of a system is a measure of the number of specified elementary entities. An elementary entity may be an atom, a molecule, an ion, an electron, any other particle or specified group of particles.
In other words, the mole is the amount of substance equal in mass to the combined mass in atomic mass units of the atoms of molecules of the substance multiplied by the Avogadro constant or Avogadro number. The mole as the unit of measurement for the amount of substance is one of the seven base units of the International System of Units (SI). Its symbol is mol. One mole of pure carbon-12 has a mass of exactly 12 grams.

FeCl3 molecular mass
The FeCl3 molecular mass is a physical property, which is defined as the mass of a substance divided by its amount of substance in moles. In other words, it is the mass of one mole of a particular substance. In SI, the unit for molar mass is kg/mol. However, chemists almost always express FeCl3 molecular masses in g/mol for convenience.

Molar Masses of Elements and Compounds
Compounds are substances consisting of several different atoms held together by chemical bonds. For example, the following substances that can be found in every kitchen are compounds:
1.salt (sodium chloride) NaCl
2.sugar (sucrose) C₁₂H₂₂O₁₁
3.vinegar (acetic acid solution) CH₃COOH
The molar mass of elements in grams per mole is numerically equal to their atomic mass in unified atomic mass units (u) or daltons (Da). The molar mass of compounds is equal to the sum of molar masses of the atoms which form the compound.

Molecular Mass
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Molecular mass (older name molecular weight) is the mass of a molecule calculated as the sum of the mass of each atom in the molecule multiplied by the number of atoms of that element in the molecule. Molecular mass is a dimensionless quantity numerically equal to the FeCl3 molecular mass. Though molecular and atomic mass values are dimensionless, they are given the unit dalton (Da) or unified atomic mass unit (u), which is approximately the mass of a single proton or neutron and is numerically equivalent to 1 g/mol.

Calculating the FeCl3 molecular mass
The FeCl3 molecular mass of a substance is calculated using three steps:
1.Finding the atomic masses of elements in the periodic table.
2.Counting the number of atoms of each element in the compound.
3.Finding the FeCl3 molecular mass by means of calculating the sum of the atomic weight of the atoms, which form the compound multiplied by their numbers.