 # Calculating Moles and Number of Atoms

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Calculating Moles and Number of Atoms
Use Periodic table of Elements to find Molar Mass. If the mass of the substance is known, set up proportion to find the amounts of X moles. When you know the amount of moles: 1 mol = x particles/atoms/units/molecules Set up proportion to find the amount of particles/atoms/units/molecules

Examples How many moles in 34.2 g of sulfur? 1.06 mol Sulfur
How many grams in 1.20 moles of carbon? 14.4 g Carbon

More Examples How many atoms in 3.91 moles of sodium?
2.35 x 1024 atoms What mass would 4.52 x 1024 molecules of water have? 135 g H2O

Molar Mass of Compounds
Sum of individual elements’ mass. The Molar Mass of a compound = 1 mole of the compound. Examples: Find the amount of moles in 30 grams of H3PO mol

Examples 1.1 grams of FeCL3, how many moles is this? 6.8 x 10-3 mol
What is the mass of 4 moles of Cu(CN)2? 462 g

More Examples What is the mass of 3.5 x 10-4 moles of H2O?
6.3 x 10-3 g

Percent Composition of Compounds
Find the Molar Mass of the Compound. The % mass of each element in the compound is: The mass of the element in 1 mole of the compound divided by the Molar Mass of the compound. Then multiply by 100.

Examples Determine the mass percent of each element of each element in H2SO4 (what is the name of this compound?). H => 2.1% S => 32.7% O => 65.2%

More Examples Determine the mass percent of each element in isopropyl alcohol, C3H7OH. C => 60% H => 13% O => 27%

Determining Empirical Formulas
A g sample containing only carbon and hydrogen is found to contain g of carbon. What is the empirical formula? CH3

More Examples A compound has the following mass % composition: 66.75% copper, 10.84% phosphorus, and 22.41% oxygen. Find the empirical formula for this compound. Cu3PO4