Chemistry 111 Exam 3 Name The Mole and Avogadro s Number o A mole is a quantity that contains 6 02 x 1023 items 1 mole of C atoms 6 02 x 1023 C atoms 1 mole of CO2 molecules 6 02 x 1023 CO2 molecules 1 mole of H2O molecules 6 02 x 1023 H2O molecules o The number 6 02 x 1023 is Avogadro s number o It can be used as a conversion factor to relate the number of moles of a substance to the number of atoms or molecules 1mol 6 02 1023atoms 6 02 1023atoms 1mol Subscripts and Moles o The subscripts in a formula give o the relationship of atoms in the formula o the moles of each element in 1 mole of a compound 1 mole C9H8O4 aspirin 9 moles C 8 moles H 4 moles O o Subscripts used for conversion factors relate moles of each element in 1 mole compound for aspirin C9H8O4 can be written as The Mole and Avogadro s Number o How many molecules are contained in 5 0 moles of carbon dioxide CO2 Page 1 Chemistry 111 Exam 3 Name Identify the original quantity and the desired quantity 5 0 mol of CO2 original quantity number of molecules of CO2 desired quantity Write out the conversion factors 6 02 1023atoms 1mol 6 02 1023atoms 1mol Set up and solve the problem 5 0mol 6 02 1023 atoms 1 mol 3 0 1025molecules of CO2 o How many O molecules are contained in 0 150 mole of aspirin C9H8O4 0 150 mol C 9 H 8O4 6 02 1023 atomsC 9 H 8 O4 1 mol C 9 H 8 O4 4 atomsO 1 mol C 9 H 8 O4 3 61 1023 atomsO Mass to Mole Conversions o The formula mass is the sum of the atomic weights of all the atoms in a compound reported in atomic mass units amu It is the mass of one molecule o Calculate the formula mass for FeSO4 Write the correct formula and determine the number of atoms of each element from the subscripts FeSO4 contains 1Fe atom 1S atom and 4O atoms Multiply the number of atoms of each element by the atomic weight and add the results 1 Fe atom x 55 85 amu 55 85amu 1 S atom x 32 07 amu 32 07amu 4 O atoms x 16 00 amu 64 00amu Formula weight of FeSO4 151 92amu add them together o The molar mass is the mass of one mole of any substance reported in grams g It is the mass of 6 02x1023 molecules o The value of the molar mass of a compound in grams equals the value of its formula mass in amu Express the numeric value of the atomic mass of any element in grams and that many grams contains 6 02 1023 atoms Page 2 Chemistry 111 Exam 3 Name o Molar Mass of K3PO4 Determine the molar mass of K3PO4 to 0 1 g Element Number of Atomic Mass Total Mass in K3PO4 Moles K P O K3PO4 3 1 4 1 39 1 g mole 31 0 g mole 16 0 g mole 117 3 g 31 0 g 64 0 g 212 3 g Mass to Mole Conversions Relating Grams to Moles o The molar mass relates the number of moles to the number of grams of a substance o In this way molar mass can be used as a conversion factor o Sample Problem How many moles are present in 100 g of aspirin C9H8O4 molar mass 180 2 g mol Identify the original quantity and the desired quantity o 100 g of aspirin original quantity o mol of aspirin desired quantity Write out the conversion factors o The conversion factor is the molar mass and it can be written in two ways o Choose the one that places the unwanted unit grams in the denominator so that the units cancel 180 2 gaspirin 1mol o 1 mol 180 2 g aspirin Set up and solve the problem o 100 g aspirin 0 555mol aspirin 1 mol 180 2 gaspirin Mass to Mole Conversions Relating Grams to Number of Atoms or Molecules o We can also use the molar mass to show the relationship between grams and number of molecules or atoms Page 3 Chemistry 111 Exam 3 Name o Sample problem How many molecules are in a 325 mg tablet of aspirin C9H8O4 molar mass 180 2 g mol Identify the original and desired quantities o 325 mg aspirin original quantity o molecules aspirin desired quantity Write out the conversion factors o To convert mg to g o Then to convert g to number of moles Set up and solve the problem 1mole 180 2g 325 mgC6 H 8 04 1 g 1000 mg Mole Calculations in Chemical Equations o A balanced chemical equation also tell us 6 02 1023molecules 1 09 1021 1mol the number of moles of each reactant that combine the number of moles of each product formed 1N2 g 1 moles of N2 1 moles of O2 2 moles of NO The coefficient 1 has been written for emphasis 1O2 g 1 moles of N2 1 moles of O2 2moles of NO 2NO g o Coefficients are used to form mole ratios which can serve as conversion factors N2 g o Mole ratios O2 g 2NO g o Use the mole ratios from the coefficients in the balanced equation to convert moles of one compound A into moles of another compound B o Sample Problem Page 4 Chemistry 111 Exam 3 Name Using the balanced chemical equation how many moles of CO are produced from 3 5 moles of C2H6 Identify the original and desired quantities o 3 5 mol C2H6 original quantity o mol CO desired quantity Write out the conversion factors 4 molCO 2molC 2 H 6 2molC 2 H 6 4molCO o Set up and solve the problem o 3 5mol C 2 H 6 4mol CO 2 mol C2 H 6 Mass to Mole Conversions Relating Moles Grams and Molecules o Sample Problem How to convert moles of reactant to grams of product Using the balanced equation how many grams of O3 are formed from 9 0 mol of O2 Convert the number of moles of reactant to the number of moles of product using a mole mole conversion factor Convert the number of moles of product to the number of grams of product using the product s molar mass Set up and solve the conversion 48 0 gO3 1 mol O3 2 mol O2 3 mol O2 9 0mol O2 290 gO3 o Sample Problem How to convert grams of reactant to grams of product Ethanol C2H6O molar mass 46 1 g mol is synthesized by reacting ethylene C2H4 molar mass 28 1 g mol with water How many grams of ethanol are formed from 14 g of ethylene 14 gC 2 H 4 1 mol C2 H 4 28 1 mol C2 H 4 1 mol C 2 H 6 O 1 mol C2 H 4 46 1 gC2 H 6O 1mol C 2 H …