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Chapter 11 Mole • SI base unit for measuring the amount of substance • The number of representative particles in exactly 12 grams of pure carbon-12 • 1 mole = 6.02 x 1023 representative particles Avogadro’s Number • 6.02 x 1023 is called Avogadro’s number • It is the number of representative particles equal to 1 mole • A representative particle is any kind of particle and depends on the substance – Water = molecule – Copper = atom – NaCl (salt) = formula unit Molar/Formula Mass • Molar/Formula mass is the mass in grams of 1 mole of any pure substance. – units are g/mol • Molar mass is equal to the atomic mass on the periodic table • Gram atomic mass: (found on periodic table) – Ex: C = 12.011 amu • This means 1 mole of Carbon = 12.011 g • Let’s practice: Find the # of grams 1 mole of the following is equal to – Al –H –O –P Formula Mass/Molar Mass • Formula or Molar mass is the mass of 1 mole of a pure substance H2O – covalent compound (metal/nonmental) H = O = total = 2 1 moles x x x 1g 16 g =2g = 16 g avg. atomic mass= 18 g • Let’s practice: Find the # of grams 1 mole of the following is equal to – H2O2 – NaCl – Ca(NO3)2 – (NH4)3PO4 – N2O4 Percent Composition • You can calculate the percentage of a certain element in a compound • Use the % Formula: (Part/Whole) x 100 = • 1st- we need the formula mass or the whole • 2nd – we need the part found in the compound • 3rd – divide and multiple by 100 • Example: What is the % of Hydrogen in H2O? 1st: Gram atomic Mass – H2O – covalent compound (metal/nonmental) H = O = total = 2 1 moles x x x 1 16 =2 = 16 avg. atomic mass= 18 g 2nd: Hydrogen has a mass of 2g 3rd: %H = (2g/18g) x 100 = 11.11% • What is the percent of oxygen in in H2O? • The percent of each element in a compound should add and equal 100. • Lets practice: Find the percent composition of each of the elements in the following compounds. – Fe2O3 – Cu2S Molar Mass can be used as a Conversion Factor • What is the mass in grams of 2.5 mol of NaCl? • Steps – 1st : get the formula/molar mass of the compound – 2nd: convert Na = 1 x 23 = 23 Cl = 1 x 35.5 = 35.5 = 58.5g ?g = 2.5 mol NaCl 58.5 g NaCl = 1 mol NaCl 146 g NaCl Avogadro’s number as a conversion factor • 1 mole = 6.02 x 1023 representative particles • Representative particles can be atoms, molecules, particles, formula units, pieces, etc • How many molecules are in 3.5 moles of CO2? ?molecules = 3.5 mol CO2 2.1 x 1024 molecules CO2 6.02 x 1023 molecules = 1 mol NaCl Volume Conversions • At STP 1 mol = 22.4 liters of a gas • What volume will 54.6 grams of CO2 occupy at STP? ?liters = 54.6 g CO2 27.8 liters of CO2 1 mol CO2 44 g CO2 22.4 liters CO2 1 mole CO2 = • Let’s practice: 1.How many grams are in 0.817 moles of C2H2O6? 2.How many moles are in 60 grams of CaC03? 3.How many formula units of CaCl2 are in 45 grams? Empirical Formulas • The simplest whole number formula/ratio of a compound. This means the equation cannot be reduced anymore. • Smallest whole number ratio • Example: An unknown sample contains 25% H and 75% C. What is the empirical formula • Steps: 1st Convert % to grams 25 % = 25 grams H (Assume you have 75 % = 75 grams C 100 grams total) 2nd Convert grams to 25 % = 25 g H x (1mol H/1g H) moles by using the = 25 mol H atomic mass 75 % = 75 g C x (1mol C/12 g C) = 6.25 mol O 3rd Divide by the smallest H = 25 mol/ 6.25 mol # of moles to get the =4 ratio C = 6.25 mol / 6.25 mol =1 4th Put numbers as subscripts of elements CH 4 in formula 5th if a whole number is not found after dividing, multiply by a factor to make it a whole # (must multiply all numbers by the same factor) Molecular Formula • Indicates the actual amount of atoms present • Must have molecular weight to determine molecular formula Steps: 1.Determine the empirical formula 2.Determine the empirical weight (molar mass of the empirical formula) 3.Divide the molecular weight given by the empirical weight you calculated – If one, then the empirical formula is the same as the molecular formula 4. If the answers from step 3 is a whole number, then take the answer and multiply all coefficients in the equation by the number. 5. If it is not a whole number you must multiple by a factor to make it a whole number then multiply each of the subscripts by it. This will give the molecular formula. Molecular Formula Example • What is the molecular formula of a compound with a molecular mass of 64 g/mol and an empirical formula of CH4? • • • • • CH4 empirical mass = (12) + (4 x 1) = 16g/mol Molecular mass = 64 g/mol 64 / 16 = 4 Multiply subscripts by 4 New formula is C4H16 Hydrates • A compound that contains a certain amount of water molecules • Example: CuSO4 . 5H2O • Copper sulfate pentahydrate • Hydrates can be dehydrated by heating • The dehydrated form can be used to absorb moisture from the air – like those packets you find in your shoe boxes – deliquescent