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Calculating Moles and Number of Atoms

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 = 6.022 x 10 23 particles/atoms/units/molecules

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Calculating Moles and Number of Atoms

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  1. 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 = 6.022 x 1023 particles/atoms/units/molecules • Set up proportion to find the amount of particles/atoms/units/molecules

  2. 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

  3. 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

  4. 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 H3PO4 0.31mol

  5. 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

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

  7. 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.

  8. 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%

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

  10. Determining Empirical Formulas • A 1.500 g sample containing only carbon and hydrogen is found to contain 1.198 g of carbon. What is the empirical formula? CH3

  11. 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

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