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Moles and Compounds

Moles and Compounds. Chemistry Ch.11 Lesson 2. Moles of Compounds. Chemical formulas are used to determine the number of each atom that make up a compound. Chemical formulas can also be used to determine the number of moles of each type of atom that make up a compound.

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Moles and Compounds

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  1. Moles and Compounds Chemistry Ch.11 Lesson 2

  2. Moles of Compounds • Chemical formulas are used to determine the number of each atom that make up a compound. • Chemical formulas can also be used to determine the number of moles of each type of atom that make up a compound. • The subscripts that identify the number of atoms in a compound can also be used to identify the number of moles.

  3. Practice Problems • Determine the number of moles of chlorine ions in 2.50 molZnCl. • Calculate the number of moles of each element in 1.25 mol glucose (C6H12O6). • Determine the number of moles of sulfate ions present in 3.00 mol iron (III) sulfate (Fe2(SO4)3). • How many moles of oxygen atoms are present in 5.00 mole diphosphoruspentoxide (P2O5)?

  4. Molar Mass of Compounds • The mass of a mole of a compound equals the sum of the mass of every particle that makes up the compound. • Use the information given by the chemical formula to determine the molar mass of a compound. • Number of moles x molar mass = number of grams. • Example Potassium chromate (K2CrO4) 2 moles potassium: 2 x 39.1 g = 78.2 g 1 mole chromium: 1 x 52.0 g = 52.0 g 4 moles oxygen: 4 x 16.0 g = 64.0 g Total: 194.2 g = molar mass of Potassium chromate

  5. Practice Problems • What is the mass of 3.25 moles of sulfuric acid (H2SO4)? • What is the mass of 4.35 x10-2 moles of zinc chloride (ZnCl2)? • How many grams of potassium permanganate (K2MnO4) are in 2.55 moles?

  6. Converting the Mass of a Compound to Moles • Determine the molar mass of each element in the compound; add them together to get the molar mass of the compound. • Divide the mass of the sample by the molar mass of the compound.

  7. Practice Problems • Determine the number of moles present in each of the following: • 22.6 g AgNO3 • 6.50 g ZnSO4 • 35.0 g HCl • 25.0 g Fe2O3 • 254 g PbCl4

  8. Converting Mass of a Compound to Number of Particles • Determine the molar mass of the compound. • Use the molar mass to determine the number of moles of the compound. • Multiply the number of moles of the compound by Avogadro’s number (6.02 x1023). • Multiply the number of each element to the previous answer. • To determine the mass of one formula unit, divide the molar mass by Avogadro’s number (6.02 x1023).

  9. Practice Problems • A sample of silver chromate (Ag2CrO4) has a mass of 25.8 g. • How many silver ions are present? • How many chromate ions are present? • What is the mass of one formula unit of silver chromate? • A sample of ethanol (C2H5OH) has a mass of 45.6 g. • How many carbon atoms does the sample contain? • How many hydrogen atoms does it contain? • How many oxygen atoms does it contain?

  10. Percent Composition • Determine the percent composition by dividing the mass ofthe element by the mass of the compound. • Multiply the number of moles by the molar mass to determine the mass. • Divide the mass of the element by the mass of the compound.

  11. Practice Problems • Determine the percent by mass of each element in calcium chloride. • Calculate the percent composition of sodium sulfate. • Which as a larger percent by mass of sulfur: H2SO3or H2S2O8? • What is the percent composition of phosphoric acid (H3PO4)?

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