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Module 3.09 Literacy Molar Mass of Compounds **Please make sure you have a periodic table, calculator and something to write with Standards and Objectives Objectives: -Calculate the molar mass of a given compound -Determine the empirical formulas from given data Standard: SC.912.P.8.7—Interpret formula representations of molecules and compounds in terms of composition and structure. Molar Mass What do we know about molar mass? What do we Want to know? Molar Mass What do we know about molar mass? -molar mass = atomic mass of an element What do we Want to know? -Calculate molar mass for a compound and use it in conversions Review: Formulas and Subscripts Determine the number of each atom in the compound below: 1. 2. 3. List the elements in the compound Determine the number of atoms of each element using subscripts For polyatomic ions (in parentheses) subscripts on the outside multiply each element of the polyatomic ion. Ca(NO3)2 Ca: N: O: This will be used to calculate molar mass for the compound. Molar mass Molar mass of an element = atomic mass for that element from the periodic table. Molar mass of a compound or molecule = the sum of atomic mass of each element x subscript (# of moles) Calculating Molar mass of a Compound 1. List the number of atoms of each element. 2. Multiply the # of each element by it’s atomic mass to determine the molar mass for each element. 3. Determine the molar mass of the compound by taking the sum of the molar mass of each element. Ex. Determine the molar mass of the compound below. Ca(NO3)2 Ca: 1 x N: 2 x O: 6 x Calculating Molar mass of a Compound 1. List the number of atoms of each element. 2. Multiply the # of each element by it’s atomic mass to determine the molar mass for each element. 3. Determine the molar mass of the compound by taking the sum of the molar mass of each element. Ex. Determine the molar mass of the compound below. Ca(NO3)2 Ca: 1 x 40.08 g =40.08 g N: 2 x 14.01 g = 28.02 g O: 6 x 15.999 g = 95.99g. (40.08 + 28.02 + 95.99) = 164.094 g/mol Molar Mass Practice Determine the Molar mass for the following compounds: H3PO4 Al(NO3)3 P2O5 Molar Mass Practice Determine the Molar mass for the following compounds: H3PO4 (3 × 1.0079 g/mol H) + (1 × 30.973 g/mol P) + (4 × 15.999 g/mol O) = 97.993 g/mol H3PO4 Al(NO3)3 (1 × 26.981 g/mol Al) + (3 × 14.006 g/mol N) + (9 × 15.999 g/mol O) = 212. 99 g/mol Al(NO3)3 P2O5 (2 × 30.973 g/mol P) + (5 × 15.999 g/mol O) = 141.94 g/mol P2O5 Using Molar Mass Calculations You can use the molar mass of compounds in dimensional analysis calculations just as you used the molar mass of individual atoms. Use the the periodic table to look up the molar mass of each element. Convert grams to moles Grams A given 1 mol A = _____ mol A molar mass g of A Convert moles to grams Moles A given molar mass g of A 1 mol A = ______ g A Using Molar Mass Calculations You can use the molar mass of compounds in dimensional analysis calculations just as you used the molar mass of individual atoms. Use the the periodic table to look up the molar mass of each element. Ex. 1 What is the mass of 3.85 moles of oxygen gas (O2)? Given: What formula will we need to use? Want: Using Molar Mass Calculations Ex. 1 What is the mass of 3.85 moles of oxygen gas (O2)? Given: 3.85 mol O2 Want: mass of O2 Which conversion will we use? convert mol to g Determine molar mass of O2: 2x 15.999 g = 31.998 g/mol 3.85 mol O2 31.998 g O2 = 123 g O2 1 mol O2 Using Molar Mass Calculations Ex. 2 How many moles of barium nitrate (Ba(NO3)2) are in 305.5 g Ba(NO3)2? Given: Which conversion will we use? Want: Using Molar Mass Calculations Ex. 2 How many moles of barium nitrate (Ba(NO3)2) are in 305.5 g Ba(NO3)2? Given: 305.5 g Ba(NO3)2 Want: moles Ba(NO3)2 Which conversion will we use? convert g to mol Determine molar mass of Ba(NO3)2 : (1 x 137.32 g) + (2 x 14.01 g) + (6 x 15.999) = 261.334 g/mol Ba(NO3)2 305.5 g Ba(NO3)2 1 mol Ba(NO3)2 = 261.334 g Ba(NO3)2 1.169 mol Ba(NO3)2 Empirical Formulas Determining Empirical Formula Empirical Formula Example Given Values Molar Mass What do we know about molar mass? -molar mass = atomic mass of an element What do we Want to know? -Calculate molar mass for a compound and use it in conversions What did we learn? -How to calculate molar mass using subscripts and atomic mass How to determine empirical formulas from data.