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

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

Intro to Quantities Review Problems One-step conversions Convert 3.50x10 24 molecules of H 2 O to moles. Convert 5.77 moles of nitric acid to the number of molecules. 3.50x10 24 molec. H 2 O 6.02x10 23 molecules 1 mol H 2 O = 5.81 mol H 2 O 5.77 mol HNO x10 23 molecules HNO 3 1 mol HNO 3 = 3.47x10 24 molec. HNO 3

Intro to Quantities Review Problems One-step conversions Convert 12.2 liters of carbon dioxide gas at STP to moles. Convert moles of nitrogen gas to volume in liters at STP L CO L CO 2 1 mol CO 2 = mol CO mol N L N 2 1 mol N 2 = L N 2

Intro to Quantities Review Problems Two-step conversions Convert 4.22 liters of oxygen gas at STP to mass in grams. Convert grams of chlorine gas to volume in liters at STP L O L O 2 1 mol O g O 2 = 6.03 g O g Cl g Cl 2 1 mol Cl L Cl 2 = L Cl 2

Intro to Quantities Review Problems Two-step conversions Convert 1.00 liter of sulfur dioxide gas at STP to the number of molecules. Convert 1.00x10 22 molecules of nitrogen dioxide gas to the volume in liters at STP L SO L SO 2 1 mol SO x10 23 molec. SO 2 = 2.68x10 22 molec. SO x10 22 molec. NO x10 23 molec. NO 2 1 mol NO L NO 2 = L NO 2

Intro to Quantities Review Problems Two-step conversions Convert 1.00 gram of gold to it’s number of atoms. Convert 1.00x10 23 atoms of mercury to the mass in grams g Au g Au 1 mol Au 6.02x10 23 atoms Au = 3.06x10 21 atoms Au 1.00x10 23 atoms Hg 6.02x10 23 atoms Hg 1 mol Hg g Hg = 33.3 g Hg

Intro to Quantities Review Problems Gas Density Conversions Determine the density of hydrogen sulfide gas at STP. If a gas has a density of 3.75 g/L at STP, what is its molar mass? 22.4 L H 2 S 1 mol H 2 S g H 2 S = 1.52 g/L H 2 S 1 L 3.75 g 1 mol 22.4 L = 84.0 g/mol

Intro to Quantities Review Problems Percent Composition Determine the percent oxygen in zinc oxide. Determine the percent nitrogen in ammonium phosphate. % oxygen = ZnO O X 100= g ZnO g O X 100= 19.7% O % N = (NH 4 ) 3 PO 4 N x 3 X 100= g/mol g/mol X 100= 28.2% N

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 Determine the molecular formula if the molar mass is g/mol 49.48%C  49.48gC 5.19%H  5.19gH 28.85%N  28.85gN 16.48%O  16.48gO 1 mol C 1 mol H 1 mol N 1 mol O g C g H g N g O = mol = mol = mol = mol ÷ mol = 4.00 = 5.00 = 2.00 = 1.00 Empirical formula: C 4 H 5 N 2 O Molecular Formula = Empirical formula Mol. Mass Emp. Mass =C 4 H 5 N 2 O g/mol g/mol = C 8 H 10 N 4 O 2