6.02 x 1023 CHAPTER 10. Mole. Avogadro s Number. Chemical Quantities The Mole: A Measurement of Matter Matter is measured in one of three ways:
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1 Chapter 10 Notes CHAPTER The Mole: A Measurement of Matter Matter is measured in one of three ways: Chemical Quantities Mole SI unit that measures the amount of a substance A mole of a substance represents 6.02 x 1023 representative particles of that substance. 1. Counting (How many?) 2. Weighing 3. Volume Avogadro s Number 6.02 x mole of substances 1
2 Representative Particle Refers to the species present in a substance: usually atoms, molecules, or formula units Types of Representative Particles Atoms: Fe, Ag, Au, Ni, Mg 7 atoms exist only as molecules. Diatomic: H 2, O 2, N 2, Cl 2, F 2, Br 2, I 2 Molecules: H 2 O, SO 2, CO 2, SCl 6 Formula Units: Ionic Compounds CaCl 2, MgSO 4, Al(OH) 3, Pb(CO 3 ) 2 Ions: Ca 2+, Br, Al 3+ Not bonded to anything Dozen = Case = Gross = Ream = Mole = What does a dozen mean? Substance How many? 1 dozen Au atoms 1 dozen H 2 O molecules 1 dozen NaCl formula units 1 dozen bananas vs. 1 dozen oranges How many are there? Do they have the same mass? 1 mole bananas vs. 1 mole oranges How many are there? One mole of Fe = 6.02 x atoms H 2 O = 6.02 x molecules CaCl 2 = 6.02 x formula units Al 3+ = 6.02 x ions 2
3 Chapter 10 Notes 1 mole of formula units Comparing Atoms Comparing Molecules 1 mol H2O Comparing Ionic Compounds 1 mol H2O2 1 mol CaCl2 1 mol Al2(CO3) x 1023 molecules 6.02 x 1023 molecules 6.02 x 1023 form units 6.02 x 1023 form units H: O: H: O: Ca: Cl: gmm = 18g gmm = 34g Al: C: O: gfm = 111 g gfm = 234g 3
4 Mass of a Mole of an Element Mass of one mole of any element is the molar mass. Gram atomic mass: mass of one mole of atoms of an element. Mass of a Mole of a Compound Molar Mass: Mass of one mole Expressed in g/mol. Gram formula mass: the mass of one mole of an ionic compound. Gram molecular mass: the mass of one mole of a molecule. Dinitrogen pentoxide Cobalt (II) nitrate Chemical Name Formula GAM, GMM, GFM (Which is it?) Molar Mass (g) 1. Sodium chloride N: O: 6.02 x molecules 6.02 x form units Co: N: O: 2. Dinitrogen pentoxide 3. Lead 4. Cobalt (II) nitrate 5. Hydrogen Significant Digits Review All numbers in scientific notation are significant. (Including zeros!) Zeros in front of significant digits are not significant. (0.023) Zeros after significant digits and after decimalare significant. (4.100) Zeros between significant digits are significant. (4005.0) Significant Digits Review (cont.) Chapter 10 involves the conversion of units and the use of conversion factors. Conversion factors do not matter when determining significant digits. When converting, your answer should be rounded to the number of significant digits as the measurement given in the problem. 4
5 What do you call an avocado that was cut up into 6.02 x pieces? guaca mole ee Moles Conversion Factors Rep Particles 1 mole 6.02 x 10 OR x mole Converting (Moles Representative Particles) 1.22 mol of Fe Converting (Representative Particles Moles) 8.72 x atoms of Mg 4.03 x 10 2 mol of CO x molecules of H 2 O 2.71 mol of MgSO x formula units of CaCl 2 Al 2 (SO 4 ) 3 C 2 H Mole Mass and Mole Volume Relationships You can use the number of moles to determine the volume or mass of an atom, molecule, or ionic compound. You can also use the volume or mass to determine the number of moles in an atom, molecule, or ionic compound. 5
6 Conversion Factors with Mass CH 4 CO 2 CaCl 2 Mole Mass Relationship The molar mass of an atom, molecule, or ionic compound is used to convert moles of a substance into grams. The molar mass is also used to convert grams into moles. Correctly use gmm, gam, or gfm. Conversion Tip Always right the conversion pathway next to the problem! Moles molecules Molecules Moles Mass Moles Moles Mass Conversion Factors Moles Mass 1 mole Molar Mass Molar Mass OR 1 mole Converting (Moles into Mass) mol of NaCl 39.2 grams of NH 3 Converting (Mass into Moles) 5.13 mol of gold grams of MgCl mol of CO grams of Calcium 6
7 Molar Mass Mass of 1 mole of a substance Different for every substance Must use correct formula and the periodic table to determine the molar mass. The molar mass does not change! Mole Volume Relationship STP: (This is very important!) Standard Temperature & Pressure Temperature: 0 C or 32 F Pressure: kpa or 1 atm Molar Volume Volume of 1 mole of a substance Gases only 22.4 L per 1 mole The molar volume is the same for all STP Molar Volume At STP, 1 mole of any gas occupies a volume of 22.4 L L is known as the molar volume of a gas L contains Avogadro s number of particles. Conversion Factors Moles STP 1 mole OR 22.4 L 22.4 L 1 mole Convert (Moles into Volume) mol SO STP 1.25 mol of STP 7
8 Convert (Volume into Moles) 20.5 L of NH STP 8.06 L of STP 1.49 L of CO STP Which conversion factor do I use to get to mole? From Formula Units From Mass From Molecules From Volume From Atoms Mass (g) Molar Road Map Mass (g) CONVERTING BETWEEN UNITS WITH MOLES Volume Rep. Particles Atoms Molecules Form units MOLE Volume Rep. Particles Atoms Molecules Form units Change from one unit to another, use the mole as a middle step. (p. 303) Rep. Particles to Moles to Mass Mass to Moles to Volume Volume to Moles to Rep. Particles STP 59.4 g of CO 2 into Liters STP 8.43 x molecules of H 2 O into Liters 71.8 g of nitrogen into molecules 9.06 x form units of CaCl 2 into Mass 8
9 STP 57.9 L of Chlorine into Mass MgCl 2 95 g = 1 mole = 6.02 x form units 18.7 L of C 2 H 6 into Rep. Particles What is the mass of 6.02 x formula units? How many molecules are in 44 grams of CO 2? Hint: the molar mass of CO 2 is 44 g/mol GAS DENSITY AND THE MOLAR MASS The density of a gas is usually measured in the units g/l. Remember that molar mass is measured in g/mol. You must convert L moles. Converting (Density of gas into Molar Mass) g/l of CO STP. Sample Problems WWhat is the density of NH 3 at STP? Determine the molar mass of NH 3. (17g/mol) Convert the molar mass into density g/l of SO STP. 9
10 Sample Problem An unknown gas is 8.20 grams & occupies 4.00 STP. Is the sample N 2 O, NO, NO 2, N 2 O 5 or N 2 O 3? Determine the density in g/l. Convert density into molar mass. Which sample has the matching molar mass. N 2 O = 44 g NO = 30 g NO 2 = 46 g N 2 O 3 = 76 g N 2 O 5 = 108 g Sample Problem Given 250 ml of gas with mass of g. Is the sample N 2 O, NO, NO 2 N 2 O 5 or N 2 O 3? Determine the density in g/l. Convert density into molar mass. Which sample has the matching molar mass? N 2 O = 44 g NO = 30 g NO 2 = 46 g N 2 O 3 = 76 g N 2 O 5 = 108 g Determining Ions and Atoms 1. How many formula units in 1 mole of Fe 2 O 3? How many "Fe" ions are in 1 formula unit? How many "O" ions are in 1 formula unit? 2. How many molecules in 1 mole of H 2 O? Sample Problems How many hydrogen atoms are there in 3.2 mol of water? H 2 O Moles into molecules into atoms How many "H" atoms are in 1 molecule? How many "O" atoms are in 1 molecule? Sample Problems How many oxygen ions are there in mol of Iron (III) oxide? Fe 2 O 3 Moles into formula units into ions 10.3 Percent Composition and Chemical Formulas Percent Composition: the percent by mass of each element in a compound. The percentages of each element should add up to 100%. Used to determine the formula of new substances. 10
11 Determining Percent Composition What is the percent composition of each element in the compound CaCO 3? Determining Percent Composition What is the percent composition of each element in the compound CO 2? Ca: 1 x 40 = 40 C: 1 x 12 = 12 O: 3 x 16 = 48 Molar Mass = 100 % Ca: 40/100 x 100 = 40% % C:12/100 x 100 = 12% % O:48/100 x 100 = 48% C: 1 x 12 = 12 O: 2 x 16 = 32 Molar Mass = 44 % C:12/44 x 100 = 27.3 % % O:32/44 x 100 = 72.7% Sample Problem You have a 500 gram sample of Carbon dioxide? What is the mass of oxygen within that sample? (Hint: first find % Composition) % C:27.3 % % O: 72.7% Determining Percent Composition What is the mass and percent composition of each element in a sample containing Magnesium and oxygen? The sample s mass is g and the mass of the oxygen is g? Magnesium = Oxygen: g Sample's Mass = g Mg: /57.89 x 100 = O: 22.98/57.89 x 100 = 39.6% Sample Problem What is the mass of calcium in 6.51 grams of calcium carbonate? % Ca: 40% % C: 12% % O: 48% Sample Problem What is the mass of sodium in 4.6 grams of sodium chloride? % Na: 39.3% % Cl: 60.7% 11
12 EMPIRICAL FORMULAS The empirical formula gives the lowest whole number ratio of the atoms of the elements in a compound. Ionic Compounds (Ionic Bonds) Always Empirical Molecular Compounds (Covalent Bonds) * NOT ALWAYS EMPIRICAL Determining Empirical Formula 1. Percent Composition 2. Assume 100 g (Use %) 3. Change to Moles (No scientific notation) 4. Divide by smallest mole 5. Change to whole number 6. Assign to elements Determining Empirical Formula Carbon = 79.9%, Hydrogen = 20.1% Determining Empirical Formula Hg = 67.6%, S = 10.8%, O = 21.6% Determining Empirical Formula Oxygen = 74.1%, Nitrogen = 25.9% 12
13 MOLECULAR FORMULAS To calculate the molecular formula, you need the empirical formula mass and the molar mass of the compound. Divide the mass of the compound by the mass of the empirical formula. Multiply that number by each number of atoms in the empirical formula. MOLECULAR FORMULAS The molecular formula can be the same as the empirical formula. Several compounds can have the same empirical formula. The empirical formula cannot be greater than a molecular formula. Determining Molecular Formulas Empirical Formula = CH 4 N Molar mass = 60.0 g/mol Determining Molecular Formulas Empirical Formula = CH 3 Molar mass is 30.0 g/mol Determining Molecular Formulas A compound consists of 58.8% C, 9.8% H, & 31.4% O. Determine the empirical formula for the compound and then the molecular formula for a compound with a molar mass of g. 13
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