![]() 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. 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. 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. That means the percent by mass of each of the elements is:Ħ.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.įinding molar mass starts with units of grams per mole (g/mol). The percent by mass of each element is given by the combined molar mass of the atoms of the element in 1 mole of H 3PO 4 divided by the molar mass of H 3PO 4, then multiplied by 100 percent. Grams of urea → moles of urea → moles of H → atoms of HĪssume that you have 1 mole of H 3PO 4. We first need to calculate the molar mass of urea: 60.06 g There are eight C atoms, ten H atoms, four N atoms, and two O atoms in caffeine, so the molecular mass is given by:Ĩ(12.01 amu) + 10(1.008 amu) + 4(14.01 amu) + 2(16.00 amu) = 194.20 amu We can find the atomic masses on the periodic table. For each element, we multiply the atomic mass of the element by the number of atoms of that element in the molecule. To calculate molecular mass, we need to sum all the atomic masses in the molecule. Grams of S → moles of S → number of S atoms ![]() We need two conversions: first from grams to moles and then from moles to number of particles (atoms). Multiplying the mass of an isotope by its fractional abundance will give the contribution to the average atomic mass of that isotope. How many grams of oxygen are needed to make 550 grams of CO 2? Possible AnswersĮach isotope contributes to the average atomic mass based on its relative abundance. Consider the following reaction: C 6H 12O 6+ 6 O 2 → 6 CO 2 + 6 H 2O. If 849.2 g of NH 3 is treated with 1223 g of CO 2 how much (NH 2) 2CO is formed?ġ0. Consider the following equation: 2 NH 3 + CO 2 → (NH 2) 2CO + H 2O. How many grams of Li are needed to produce 7.79 g of H 2?ĩ. Consider the following reaction: 2 Li + 2 H 2O → 2 LiOH + H 2. If 968 g of C 6H 12O 6 is consumed, what is the mass of CO 2 produced?Ĩ. Consider the reaction: C 6H 12O 6 + 6 O 2 → 6 CO 2+ 6 H 2O. Balance the following equation with smallest whole number coefficients:ħ. Calculate the percent composition by mass of H, P, and O in this compound.Ħ. How many hydrogen atoms are present in 43.8 g of urea ?ĥ. Calculate the molecular mass (in amu) of caffeine (C 8H 10N 4O 2).Ĥ. How many atoms of sulfur are in 25.1 g of S?ģ. Calculate the average atomic mass of copper.Ģ. Copper has two stable isotopes 63 29Cu (atomic mass = 62.93 amu 69.09% natural abundance) and 65 29Cu (atomic mass = 64.9278 amu 30.91 % natural abundance).
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