Chem Mole Review Key

The Mole Review Honors Chemistry Show your work AND include units. 1. Determine the number of moles in 3.25 x 10^24 atoms of lead. 3.25 x 10^24 atoms Pb x 1 mol Pb / 6.02 x 10^23 atoms = 5.4 mol Pb 2. How many formula units are in 2.24 mol of KNO₃? 2.24 mol KNO₃ x 6.02 x 10^23 formula units / 1 mol = 1.35 x 10^24 formula units KNO₃ 3. Calculate the molar mass of ammonium nitrate. NH₄NO₃ 1N: 1(14.01) = 14.01 4H: 4(1.01) = 4.04 1N: 1(14.01) = 14.01 3O: 3(16) = 48 → 80.06 g/mol 4. What is the mass of 1.25 mol Ca(OH)₂? 40.08 + 2(16) + 2(1.01) = 74.1 g/mol 1.25 mol x 74.1 g / 1 mol = 92.6 g Ca(OH)₂ 5. How many moles of AgNO₃ are contained in 24 g? 107.9 + 14.01 + 3(16) = 169.91 g/mol 24 g AgNO₃ x 1 mol / 169.91 g = 0.14 mol AgNO₃ 6. Determine the number of atoms in 3.20 g of copper. 3.20 g Cu x 1 mol Cu / 63.55 g Cu x 6.02 x 10^23 atoms Cu / 1 mol Cu = 3.03 x 10^22 atoms Cu 7. What is the mass of 2.34 x 10^24 molecules of H₂O₂? 2.34 x 10^24 molecules H₂O₂ x 1 mol H₂O₂ / 6.02 x 10^23 molecules x 34.02 g H₂O₂ / 1 mol H₂O₂ = 132.29 g H₂O₂ 8. Calculate the percent composition of sucrose (C₁₂H₂₂O₁₁). %C = (144.1/342.32) * 100 = 42.1% %H = (22.22/342.32) * 100 = 6.5% %O = (176/342.32) * 100 = 51.4% 9. When an 88-g sample of a compound containing only Mg and Cl is decomposed, 22.4 g of Cl is obtained. What is the percent composition of this compound? %Cl = (22.4/88) * 100 = 25.5% %Mg = 100 - 25.5 = 74.5% Formula for this compound: MgCl₂ 10. Determine the empirical formula for a compound that contains 174.86 g Fe and 75.14 g O. 174.86 g Fe x 1 mol Fe / 55.85 g Fe = 3.13 mol Fe 75.14 g O x 1 mol O / 16 g O = 4.70 mol O (Fe₁₀₅O₁₅)₂ → Fe₂O₃ 11. Determine the molecular formula of a compound whose molar mass is 92.0 g/mol and empirical formula is NO₂. (NO₂)₂ = N₂O₄ 12. Explain how to decide which representative particle is used to describe a substance. atoms - element molecules - covalently bonded compound formula units - ionically bonded compound 13. Explain the difference between atomic mass (amu) and molar mass (g). atom ↔ mole