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. The formula weight is simply the weight in atomic mass units of all the atoms in a given formula. In each of these moles of substances, there are 6. A single unit of NaCl has a mass of 58.45 amu NaCl has a molar mass of 58.45 g. A molecule of H 2 O has a mass of about 18.01 amu 1 mol H 2 O has a mass of 18.01 g. When calculating molecular weight of a chemical compound, it tells us how many grams are in one mole of that substance. One molecule has a mass of 1.0079 + 1.0079 2.0158 amu, while 1 mol H 2 has a mass of 2.0158 g. For bulk stoichiometric calculations, we are usually determining molar mass, which may also be called standard atomic weight or average atomic mass.įinding molar mass starts with units of grams per mole (g/mol). 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. This site explains how to find molar mass. There are two types of molar pregnancy complete molar pregnancy and partial molar pregnancy. That organ also is known as the placenta. These cells typically become the organ that feeds a growing fetus. It involves unusual growth of cells called trophoblasts. The reason is that the molar mass of the substance affects the conversion. A molar pregnancy is a rare complication of pregnancy. To complete this calculation, you have to know what substance you are trying to convert. 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.Ī common request on this site is to convert grams to moles. Learn more about calculating the weight of H 2 O on our water weight calculator. The formula to calculate the molecular weight based on the atomic weights looks like this: molar mass 1.00794 (H) + 1.00794 (H) + 15.9994 (O) Therefore, the molar mass of H 2 O is 18.01528 g/mol. If the formula used in calculating molar mass is the molecular formula, the formula weight computed is the molecular weight. The atomic mass of hydrogen is 1.00794 and oxygen is 15.9994. These relative weights computed from the chemical equation are sometimes called equation weights. 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.įormula weights are especially useful in determining the relative weights of reagents and products in a chemical reaction.
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