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Intro to Quantities Review Problems

Intro to Quantities Review Problems. These are the calculations you should be able to perform: Sum of molar mass for a compound Convert mass  mole Convert mole  mass Convert mole  number of particles Convert number of particles  mole Convert mole  gas volume at STP

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Intro to Quantities Review Problems

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  1. Intro to Quantities Review Problems • These are the calculations you should be able to perform: • Sum of molar mass for a compound • Convert mass  mole • Convert mole  mass • Convert mole  number of particles • Convert number of particles  mole • Convert mole  gas volume at STP • Convert gas volume at STP  mole • Determine gas density from molar mass at STP • Determine molar mass from gas density at STP • Determine % composition of a compound • Determine empirical & molecular formula given composition data These steps can be combined into 2 step conversions

  2. Intro to Quantities Review Problems One-step conversions Convert 25.5 grams of potassium chloride to moles. Put 1 mole here 1 mol KCl 25.5 g KCl = 0.342 mol KCl 74.551 g KCl ÷ Put molar mass here Divide Convert 0.334 moles of hydrochloric acid to mass in grams. X Multiply Put molar mass here 36.461g HCl 0.334 mol HCl = 12.2 g HCl 1 mol HCl Put 1 mole here

  3. Intro to Quantities Review Problems One-step conversions Convert 3.50x1024 molecules of H2O to moles. 1 mol H2O 3.50x1024 molec. H2O = 5.81 mol H2O 6.02x1023 molecules Convert 5.77 moles of nitric acid to the number of molecules. 6.02x1023 molecules HNO3 5.77 mol HNO3 = 3.47x1024molec. HNO3 1 mol HNO3

  4. Intro to Quantities Review Problems One-step conversions Convert 12.2 liters of carbon dioxide gas at STP to moles. 1 mol CO2 12.2 L CO2 = 0.545 mol CO2 22.4 L CO2 Convert 0.0185 moles of nitrogen gas to volume in liters at STP. 22.4 L N2 0.0185 mol N2 = 0.414 L N2 1 mol N2

  5. Intro to Quantities Review Problems Two-step conversions Convert 4.22 liters of oxygen gas at STP to mass in grams. 1 mol O2 31.9988 g O2 4.22 L O2 = 6.03 g O2 22.4 L O2 1 mol O2 Convert 0.802 grams of chlorine gas to volume in liters at STP. 1 mol Cl2 22.4 L Cl2 0.802 g Cl2 = 0.253 L Cl2 70.906 g Cl2 1 mol Cl2

  6. Intro to Quantities Review Problems Two-step conversions Convert 1.00 liter of sulfur dioxide gas at STP to the number of molecules. 1 mol SO2 6.02x1023molec. SO2 1.00 L SO2 = 2.68x1022 molec. SO2 22.4 L SO2 1 mol SO2 Convert 1.00x1022 molecules of nitrogen dioxide gas to the volume in liters at STP. 1 mol NO2 22.4 L NO2 1.00x1022 molec. NO2 = 0.372 L NO2 6.02x1023 molec. NO2 1 mol NO2

  7. Intro to Quantities Review Problems Two-step conversions Convert 1.00 gram of gold to it’s number of atoms. 1 mol Au 6.02x1023atoms Au 1.00 g Au = 3.06x1021atoms Au 196.96655g Au 1 mol Au Convert 1.00x1023 atoms of mercury to the mass in grams. 1 mol Hg 200.59 g Hg 1.00x1023 atoms Hg = 33.3 g Hg 6.02x1023 atoms Hg 1 mol Hg

  8. Intro to Quantities Review Problems Gas Density Conversions Determine the density of hydrogen sulfide gas at STP. 1 mol H2S 34.081 g H2S = 1.52 g/L H2S 22.4 L H2S 1 mol H2S If a gas has a density of 3.75 g/L at STP, what is its molar mass? 3.75 g 22.4 L = 84.0 g/mol 1 L 1 mol

  9. Intro to Quantities Review Problems Percent Composition Determine the percent oxygen in zinc oxide. O 15.9994 g O % oxygen = X 100 = X 100 = 19.7% O ZnO 81.408 g ZnO Determine the percent nitrogen in ammonium phosphate. N x 3 42.02 g/mol % N = X 100 = X 100 = 28.2% N (NH4)3PO4 149.09 g/mol

  10. Intro to Quantities Review Problems Empirical & Molecular Formula Determine the empirical formula of caffeine if its composition is 49.48% C; 5.19% H; 28.85% N; 16.48% O 49.48%C  49.48gC 5.19%H  5.19gH 28.85%N  28.85gN 16.48%O  16.48gO 1 mol C =4.1196 mol ÷1.0300 mol = 4.00 12.011g C 1 mol H Empirical formula: C4H5N2O =5.1491 mol ÷1.0300 mol = 5.00 1.00794 g H 1 mol N =2.0597 mol ÷1.0300 mol = 2.00 14.0067 g N 1 mol O =1.0300 mol ÷1.0300 mol = 1.00 15.9994 g O Determine the molecular formula if the molar mass is 194.2 g/mol Mol. Mass 194.2 g/mol Molecular Formula = Empirical formula =C4H5N2O = C8H10N4O2 Emp. Mass 97.10 g/mol

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