![]() ![]() The molar mass of a compound is the mass in grams of 1 mole of that substance, a property expressed in units of grams per mole (g/mol)īecause the definitions of both the mole and the formula mass are based on the same reference substance, 12C, the molar mass of any compound is numerically equivalent to its formula weight in amu. The masses of 1 mole of different compunds, however, are different, since the masses of the individual molecules are drastically different. Similar to atoms, 1 mole of any compound contains the same number of molecules as 1 mole of any other compund. These relative weights computed from the chemical equation are sometimes called equation weights.\). The periodic table lists the atomic mass of carbon as 12.011 amu the average molar mass of carbonthe mass of 6.022 × 10 23 carbon atomsis therefore 12. Using the chemical formula of the compound and the periodic table of elements, we can add up the atomic weights and calculate molecular weight of the substance.įormula weights are especially useful in determining the relative weights of reagents and products in a chemical reaction. The molar mass of any substance is its atomic mass, molecular mass, or formula mass in grams per mole. The percentage by weight of any atom or group of atoms in a compound can be computed by dividing the total weight of the atom (or group of atoms) in the formula by the formula weight and multiplying by 100. If the formula used in calculating molar mass is the molecular formula, the formula weight computed is the molecular weight. The formula weight is simply the weight in atomic mass units of all the atoms in a given formula. When calculating molecular weight of a chemical compound, it tells us how many grams are in one mole of that substance. This site explains how to find molar mass.įinding molar mass starts with units of grams per mole (g/mol). The reason is that the molar mass of the substance affects the conversion. Our final answer is expressed to four significant figures. The calculated value makes sense because it is almost four times times the mass for 1 mole of aluminum. Element Symbol Atomic weight Atoms Mass percent Potassium: K: 39.0983: 1: 100. Compound Moles Weight, g K: Elemental composition of K. To complete this calculation, you have to know what substance you are trying to convert. 3.987 molAl × 26.98gAl 1 molAl 107.6gAl 3.987 mol Al × 26.98 g Al 1 mol Al 107.6 g Al. Enter a chemical formula to calculate its molar mass and elemental composition: Molar mass of K (Potassium) is 39.09830 ± 0.00010 g/mol. For bulk stoichiometric calculations, we are usually determining molar mass, which may also be called standard atomic weight or average atomic mass.Ī common request on this site is to convert grams to moles. This is not the same as molecular mass, which is the mass of a single molecule of well-defined isotopes. This is how to calculate molar mass (average molecular weight), which is based on isotropically weighted averages. The atomic weights used on this site come from NIST, the National Institute of Standards and Technology. In chemistry, the formula weight is a quantity computed by multiplying the atomic weight (in atomic mass units) of each element in a chemical formula by the number of atoms of that element present in the formula, then adding all of these products together. ![]()
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