5 Avogadro’s Number Avogadro’s Number = 6.022 X 1023 Is a very large number because it is used to count extremely small particles.
6 Conversion of a Mole to a Particle 1 mole = 6.02 x 1023# of moles x 6.02 x 1023 representative particles = # of representative particles
7 Ex: How many molecules are in 3.5 moles of sucrose? 3.5 moles sucrose x 6.02 x 1023 molecules = mole sucrose= 2.11 x 1024 molecules of sucrose
8 Conversion of a Particle to a Mole Reverse conversion factor to solve for # of molesEx: How many moles are in 4.50 x 1024 atoms of zinc?4.50 x 1024 atoms Zn x 1 mol Zn6.02 x 1023 atoms Zn= 7.48 mol Zn
10 11.2 Mass and the MoleJust as a dozen bricks and a dozen feathers don’t have the same mass, moles of different substances also have different masses.
11 Molar mass- mass in grams of one mole of any pure substance The molar mass of any element is numerically equal to its atomic mass and has the units g/mol
12 Using Molar MassEx: What is the mass in grams of moles of chromium?Moles Cr x grams Cr = grams Cr1 mole Crmol Cr x g Cr = 2.34 g Cr1 mol Cr
13 Mols MassParticles(atoms, molecules, formula unit)
14 Converting Mass to Atoms and Atoms to Mass Ex: How many atoms of gold are in a pure nugget having a mass of 25.0 g?Known:Mass = 25.0 g AuMolar mass Au = g/mol AuUnknown:Number of atoms = ? Atoms Au
15 Mass Au x 1 mole Au = moles Au # g Au25.0 g Au x mol Au = ? mol Aug Au= mol AuHalf way there!!
16 Moles Au x 6.02 x 1023 atoms Au =1 mole Au0.127 mol Au x 6.02 x 1023 atoms Au1 mol Au= 7.65 x 1022 atoms AuMass must always be converted to moles before being converted to atoms, and atoms must be converted moles before calculating their mass.
17 11.3 Moles of CompoundsChemical formula indicates types of atoms and number of each in one unit of the compound
18 Ex: CCl2F2Carbon = one atomChlorine = 2 atomsFluorine = 2 atomsRatio of carbon to chlorine to fluorine is 1 : 2 : 2
19 Conversions with Chemical Formulas How many moles of fluorine atoms are in 5.50 moles of freon (CCl2F2)?5.50 mol CCl2F2 x 2 mol F atoms = 11.0 mol F atoms mol CCl2F2
20 Molar Mass of Compounds Mass of a mole of a compound equals the sum of the masses of every particle that makes up the compound.Suppose you want to determine the molar mass of potassium chromate (K2CrO4)
21 # moles x molar mass = # grams 2.000 mol K x g K = g K1 mol K1.000 mol Cr x g Cr = g Cr1 mol Cr4.000 mol O x g O = g O1 mol O
23 Converting Moles of a Compound to Mass Step 1: Calculate molar mass of the compound.Step 2: Convert moles to grams using the molar mass as a conversion factor.
24 Converting Moles to Mass Convert 2.50 mol CHCl3 to mass in grams.Step one: Calculate the number of grams in one mole of CHCl3 = gramsStep up problem as beforeWhat’s given What you wantWhat you want to get rid of2.5 mol CHCl grams of CHCl31 mol of CHCl3= grams of CHCl3
25 Converting Mass of a Compound to Moles Use inverse of mole to mass conversion factor
26 Converting Mass of a Compound to Number of Particles Step 1: Convert given mass to moles by using the molar mass as a conversion factor.Step 2: Convert moles to number of representative particles by multiplying by Avogadro’s number.
27 11.4 Empirical and Molecular Formulas Percent Composition- percent by mass of each element in a compound% composition = mass of element x 100mass of compound
28 Percent Composition from the Chemical Formula Percent composition is always the same, regardless of the size of the sampleTo determine percent composition, assume a sample size of one mole
29 What is the percent composition of water? Percent Hydrogen:2.02 g H x 100 = 11.2% H18.02 g H2OPercent Oxygen:16.00 g O x 100 = 88.80% OThink about it as a cookie with parts, calculate its percentage
39 Molecular FormulaMolecular Formula- specifies the actual number of atoms of each element in one molecule or formula unit of the substance
40 Molecular formula = (empirical formula) n n is the factor by which the subscripts in the empirical formula must be multiplied to obtain molecular formula
41 Determining Molecular Formula Empirical formula: C2H3O2Molar Mass C2H3O2 = g C2H3O2 (calculated value)Molar Mass succinic acid = g(given value)I have one dozen eggs and they weigh 1 lb, I have 10 pounds of egg, how much dozen do I have?I have one mol of oxygen, it weighs 16g, but I did this experiment I now I have 32g of oxygen, how much mols of oxygen do I have?
42 n = molar mass succinic acid molar mass C2H3O2 (empirical formula)n = g = 2.0059.04 g(C2H3O2) 2 = C4H6O4