What is the molar mass of a substance?
The molar mass is the mass of a given chemical element or chemical compound (g) divided by the amount of substance (mol). The molar mass of a compound can be calculated by adding the standard atomic masses (in g/mol) of the constituent atoms.
Molecular mass. It is calculated as the sum of the atomic weights of each constituent element multiplied by the number of atoms of that element in the molecular formula. The molecular mass of small to medium size molecules, measured by mass spectrometry, determines stoichiometry.
- The molecular weight is the mass of one mole of a substance. Usually, the units used for this are grams per mole. In this movie, we show how to calculate the molecular weight of a substance from the atomic weights given on the periodic table.
- Go to periodic table and determine the atomic mass average (atomic weight) of each element. Multiply each atomic mass by the number of atoms in the formula. Add up the results of step three: 2.015+32.066+63.998 = 98.079 = molar mass of sulfuric acid.
- Definition of equivalent weight. : the mass of a substance especially in grams that combines with or is chemically equivalent to eight grams of oxygen or one gram of hydrogen : the atomic or molecular weight divided by the valence.
The molar mass is the mass of all the atoms in a molecule in grams per mole. To calculate the molar mass of a molecule, we first obtain the atomic weights from the individual elements in a periodic table. We then count the number of atoms and multiply it by the individual atomic masses.
- Multiply Moles by the Avogadro Constant. Multiply the number of moles by the Avogadro constant, 6.022 x 10^23, to calculate the number of molecules in your sample. In the example, the number of molecules of Na2SO4 is 0.141 x 6.022 x 10^23, or 8.491 x 10^22 molecules of Na2SO4.
- The molar mass is the mass of all the atoms in a molecule in grams per mole. To calculate the molar mass of a molecule, we first obtain the atomic weights from the individual elements in a periodic table. We then count the number of atoms and multiply it by the individual atomic masses.
- The units are different: * molecular weight is in atomic mass units, because it's the mass of one molecule. * molar mass is in grams per mole, because it's the mass of a mole of molecules. But the numbers are the same, at low precision (typically 1 decimal place).
However, because densities of different substances vary, weight and volume aren't very good guidelines to amount. A small, dense object may weigh a lot, and have more molecules of substance than a large, hollow object. The molar mass of a substance is defined relative to the mole.
- Using a calculator, divide the number of grams by the molar mass. The result is the number of moles in your element or compound. For example, imagine you have 2 g of water, or H2O, and you want to convert it to moles. The molecular mass of H2O is 18g/mol.
- To calculate the atomic mass of a single atom of an element, add up the mass of protons and neutrons. Example: Find the atomic mass of an isotope of carbon that has 7 neutrons. You can see from the periodic table that carbon has an atomic number of 6, which is its number of protons.
- Definition. Molar mass is a ratio that is used to convert a mass measurement to an amount of substance. This amount is expressed as a number of particles, such as atoms, molecules or ions. It is the ratio between the mass of something and the number of particles that form it.
Updated: 21st October 2019