Quantitative Composition of Compounds Chapter 7Chapter Outline7.1 The MoleThe mass of a single atom is too small to measure on a balance.Slide 5Slide 6Slide 7Slide 8Slide 9If 10,000 people started to count Avogadro’s number and counted at the rate of 100 numbers per minute each minute of the day, it would take over 1 trillion years to count the total number.Slide 11Slide 12Slide 13ExamplesSpecies Quantity Number of H atomsSpecies Quantity Number of H2 moleculesSpecies Quantity Number of Na atomsSpecies Quantity Number of Fe atomsSpecies Quantity Number of C6H6 moleculesSlide 20Slide 21Slide 22ProblemsHow many moles of iron does 25.0 g of iron represent?Slide 25Slide 26What is the mass of 0.365 moles of tin?Slide 287.2 Molar Mass of CompoundsThe molar mass of a compound can be determined by adding the molar masses of all of the atoms in its formula.Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37In dealing with diatomic elements (H2, O2, N2, F2, Cl2, Br2, and I2), distinguish between one mole of atoms and one mole of molecules.Slide 39Slide 40Slide 41Slide 42Slide 43Slide 447.3 Percent Composition of CompoundsPercent composition of a compound is the mass percent of each element in the compound.Slide 47Slide 48Slide 49Slide 50Slide 51Slide 52Slide 53Slide 54Slide 557.4 Empirical Formula versus Molecular FormulaSlide 57Slide 58Slide 59Slide 61Slide 62Slide 63Two compounds can have identical empirical formulas and different molecular formulas.Slide 657.5 Calculating Empirical FormulasSlide 67Slide 68Slide 69Slide 70Slide 71Slide 72Slide 73Slide 74Slide 75Slide 76Slide 77Slide 78Slide 797.6 Calculating the Molecular Formula from the Empirical FormulaSlide 81Slide 82Slide 831Quantitative Composition of Compounds Chapter 7 Quantitative Composition of Compounds Chapter 7 Hein and Arena Eugene Passer Chemistry Department Bronx Community College© John Wiley and Sons, IncVersion 2.012th Edition2Chapter Outline7.1 The Mole 7.2 Molar Mass of Compounds7.3 Percent Composition of Compounds7.4 Empirical Formula versus Molecular Formula7.5 Calculating Empirical Formulas7.6 Calculating the Molecular Formula from the Empirical Formula37.17.1The MoleThe Mole4The mass of a single atom is too small to measure on a balance.mass of hydrogen atom = 1.673 x 10-24 g5This is aninfinitesimal mass1.673 x 10-24 g6•Chemists have chosen a unit for counting atoms.•That unit is the•Chemists require a unit for counting which can express large numbers of atoms using simple numbers.MOLE71 mole = 6.022 x 1023 objects8LARGE6.022 x 1023is a verynumber96.022 x 1023isnumberAvogadro’s Number10 If 10,000 people started to count Avogadro’s number and counted at the rate of 100 numbers per minute each minute of the day, it would take over 1 trillion years to count the total number.111 mole of any element contains 6.022 x 1023 particles of that substance.12The atomic mass in grams of any element23 contains 1 mole of atoms.13This is the same number of particles6.022 x 1023 as there are in exactly 12 grams of C12614ExamplesExamplesExamplesExamples15 Species Quantity Number of H atomsH1 mole6.022 x 102316 Species Quantity Number of H2 moleculesH21 mole6.022 x 102317 Species Quantity Number of Na atomsNa1 mole6.022 x 102318 Species Quantity Number of Fe atomsFe1 mole6.022 x 102319 Species Quantity Number of C6H6 moleculesC6H61 mole6.022 x 1023201 mol of atoms = 6.022 x 1023 atoms6.022 x 1023 molecules6.022 x 1023 ions1 mol of molecules =1 mol of ions =21•The molar mass of an element is its atomic mass in grams.•It contains 6.022 x 1023 atoms (Avogadro’s number) of the element.22ElementAtomic massMolar massNumber of atomsH 1.008 amu 1.008 g 6.022 x 1023Mg 24.31 amu 24.31 g 6.022 x 1023Na 22.99 amu 22.99 g 6.022 x 102323ProblemsProblemsProblemsProblems24Atomic mass iron = 55.85How many moles of iron does 25.0 g of iron represent?Conversion sequence: grams Fe → moles Fe1 mol Fe(grams Fe)55.85 g Fe� �� �� �1 mol Fe(25.0 g Fe)55.85 g Fe� �=� �� �0.448 mol FeSet up the calculation using a conversion factor between moles and grams.25Atomic mass iron = 55.85Conversion sequence: grams Fe → atoms Fe236.022 x 10 atoms Fe(grams Fe)55.85 g Fe� �� �� �How many iron atoms are contained in 25.0 grams of iron?236.022 x 10 atoms Fe(25.0 g Fe)55.85 g Fe� �=� �� �232.70 x 10 atoms FeSet up the calculation using a conversion factor between atoms and grams.26Molar mass Na = 22.99 gConversion sequence: atoms Na → grams Na2322.99 g Na(atoms Na)6.022 x 10 atoms Na� �� �� �What is the mass of 3.01 x 1023 atoms of sodium (Na)?232322.99 g Na(3.01 x 10 atoms Na)6.022 x 10 atoms Na� �=� �� �11.5 g NaSet up the calculation using a conversion factor between grams and atoms.27Atomic mass tin = 118.7What is the mass of 0.365 moles of tin?Conversion sequence: moles Sn → grams Sn1 molar mass Sn(moles Sn)1 mole Sn� �� �� �118.7 g Sn(0.365 moles Sn)1 mole Sn� �=� �� �43.3 g Sn Set up the calculation using a conversion factor between grams and atoms.282(2.00 mol O )23226.022 x 10 molecules O1 mol O� �� �� �22 atoms O1 molecule O� �� �� �Conversion sequence: moles O2 → molecules O → atoms O23226.022 x 10 molecules O1 mol O� �� �� �How many oxygen atoms are present in 2.00 mol of oxygen molecules?Two conversion factors are needed:22 atoms O1 mol O� �� �� �24= 2.41 x10 atoms O297.27.2Molar Mass of Molar Mass of CompoundsCompounds30The molar mass of a compound can be determined by adding the molar masses of all of the atoms in its formula.312 C = 2(12.01 g) = 24.02 g6 H = 6(1.01 g) = 6.06 g1 O = 1(16.00 g) = 16.00 g 46.08 gCalculate the molar mass of C2H6O.321 Li = 1(6.94 g) = 6.94 g1 Cl = 1(35.45 g) = 35.45 g4 O = 4(16.00 g) = 64.00 g106.39 gCalculate the molar mass of LiClO4.33Calculate the molar mass of (NH4)3PO4 .3 N = 3(14.01 g) = 42.03 g12 H = 12(1.01 g) = 12.12 g1 P = 1(30.97 g) = 30.97 g4 O = 4(16.00 g) = 64.00 g149.12 g34Avogadro’s Number of Particles6 x 1023 ParticlesMolar Mass1 MOLE351 MOLE CaAvogadro’s Number ofCa atoms6 x 1023 Ca atoms40.078 g Ca361 MOLE H2OAvogadro’s Number ofH2O molecules6 x 1023 H2O molecules18.02 g H2O37H Cl HCl6.022 x 1023 H atoms6.022 x 1023 Cl atoms6.022 x 1023 HCl molecules1 mol H atoms 1 mol Cl atoms1 mol HCl molecules1.008 g H 35.45 g Cl 36.46
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