Finding the molar mass by means of calculating the sum of the atomic weight of the atoms, which form the compound multiplied by their numbers.įor example, let us calculate the molar mass of the acetic acid.Counting the number of atoms of each element in the compound.Finding the atomic masses of elements in the periodic table.The molar mass of a substance is calculated using three steps: 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. Molecular mass is a dimensionless quantity numerically equal to the molar mass. 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. However, chemists almost always express molar masses in g/mol for convenience. In SI, the unit for molar mass is kg/mol. In other words, it is the mass of one mole of a particular substance. The molar mass is a physical property, which is defined as the mass of a substance divided by its amount of substance in moles. One mole of pure carbon-12 has a mass of exactly 12 grams. 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). 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. An elementary entity may be an atom, a molecule, an ion, an electron, any other particle or specified group of particles.Īvogadro constant N A = 6.02214076×10²³ mol⁻¹ The amount of substance, symbol n, of a system is a measure of the number of specified elementary entities. This number is the fixed numerical value of the Avogadro constant, N A, when expressed in the unit mol⁻¹ and is called the Avogadro number. One mole contains exactly 6.02214076×10²³ elementary entities. The mole, symbol mol, is the SI unit of the amount of substance. The mole is used to express the amounts of reactants and products of chemical reactions. In chemistry, it is important to measure their amounts accurately. All substances consist of atoms or molecules.
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