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. These relative weights computed from the chemical equation are sometimes called equation weights. 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.įormula weights are especially useful in determining the relative weights of reagents and products in a chemical reaction. 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. Thefollowing experimental data are collected: mass of gas, 12.5 mg, pressure of gas, 24.8torr, temperature, 25.0 oC and volume of flask, 125.0 mL. To find its molar mass, youmeasure the pressure of the gas in a known volume at a known temperature. When calculating molecular weight of a chemical compound, it tells us how many grams are in one mole of that substance. A new boron hydride, BxHy has been isolated. 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. The reason is that the molar mass of the substance affects the conversion. To complete this calculation, you have to know what substance you are trying to convert. 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.Ī common request on this site is to convert grams to moles.
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