Molar Mass vs Molecular Mass
Atoms can join together in various combinations to form molecules and other compounds. Molecular structures give the exact ratios of atoms, thus we can write molecular formulas for compounds. These are important in determining the molecular masses or molar masses. Molecules are characterized with their masses. Knowing this is really useful in laboratory work, when measuring the compounds for reactions.
Molecular mass of a compound is the mass of a one molecule. This is measured by atomic mass units (amu). 1 atomic mass unit is the one twelfth of the mass of a C-12 isotope. When a mass of a molecule is divided by the mass of one twelfth of the mass of a C-12 isotope, its relative mass is obtained. Molecular mass differs due to the isotopes in which molecule is made up of. When calculating the molecular mass, the relevant isotopic mass should be considered.
This is also known as molecular weight. It is the mass of a substance for a given amount. The SI unit for the molar mass is g mol-1. This gives the amount of the atoms/molecules/compounds present in one mole of the substance. In other words, it is the mass of Avogadro number of atoms/molecules or compounds. It is important to measure the weight of atoms and molecules in the practical scenario. But it is difficult to weigh them as individual particles, since their masses are really small according to the normal weighing parameters (such as grams or kilograms). Therefore, to fulfill this gap and to measure the particles in a macroscopic level molar mass concept is useful. The definition of molar mass is directly related to the carbon-12 isotope. The mass of one mole of carbon-12 atoms is exactly 12 grams, which is its molar mass, it is exactly 12 grams per mole. Molar mass of molecules containing the same atom like O2 or N2 is calculated by multiplying the number of atoms by the molar mass of the atoms. Molar mass of the compounds like NaCl or CuSO4 is calculated by adding the atomic masses of each atom.
What’s the difference between Molar Mass and Molecular Mass?
- Molecular mass gives the mass of a single molecule (sum of the atomic masses in the molecule), whereas molar mass gives the average mass of the molecule (mass of Avogadro number of molecules).
- Therefore, the molecular mass of a molecule containing heavier isotopes can be few units higher than the molar mass.
- Otherwise, the value of the molar mass and molecular mass is quiet the same for a similar molecule; only the units are different. The unit of the molecular mass is amu, and the unit of the molar mass is gmol-1.
- It is accurate to use the molecular mass in calculations of higher amounts of molecules than using the molar mass.
- Molar mass is a measurement, which can be given to atoms, molecules or compounds. But molecular mass is only determined in the molecules. If it is the mass of an atom, a different terminology called atomic mass is used.