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Published byAlexandra Sarah Floyd Modified over 6 years ago

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**3.8 -3.9 Formula Mass and Composition of Compounds**

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**Molar Mass Equivalent to formula mass, except with the units g/mol.**

What is the molar mass of sodium bicarbonate? NaHCO3 Na = g/mol H = 1.01 g/ mol C = g/mol O = g/mol X 3 = g/mol NaHCO3 = g/mol g/mol g/mol g/mol = g/mol

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Formula Mass Formula mass (a.k.a. molecular mass or molecular weight) is the sum of the atomic masses of all the atoms that make up a compound. Unit is amu. What is the formula mass of H2O? H = 1.01 amu X 2 = 2.02 amu O = amu H2O = amu amu = amu

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**Composition of Compounds**

Mass percent composition is used to calculate the percentage of an element in a compound . mass of the element in 1 mol of compound % mass of an element = X 100 mass of 1 mol of compound Calculate the mass percent of sodium in sodium oxide. Formula is Na2O 45.98 g / mol % mass of Na = X 100 = % 61.98 g/mol

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**Using Molar Mass to Count Molecules by Weighing**

Find the number of ibuprofen molecules in a tablet containing mg of ibuprofen (C13H18O2) Step 1: Convert mg g mg = g Step 2: Convert g mol 0.200 g C13H18O g C13H18O2 = X mol C13H18O2 X = 9.69X10-4 mol C13H18O2 Step 3: Covert mol molecules 9.69X10-4 mol C13H18O mol C13H18O2 = X X1023 molecules C13H18O2 X = 5.84X1020 molecules C13H18O2

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**Mass Percent Composition as a Conversion Factor**

What mass (in grams) of iron(III) oxide contains 58.7 g of iron? Iron(III) oxide is 69.94% iron by mass. 69.94 g Fe g Fe = g Fe2O X X = g Fe2O3

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**Conversion Factors from Chemical Formulas**

Determine the mass of oxygen in 7.2 g sample of Al2(SO4) g/mol O % mass oxygen = X g/mol Al2(SO4)3 % mass oxygen = % g O X = g Al2(SO4)3 7.2 g Al2(SO4)3 X = 4.04 g oxygen

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**Pg. 132 (Just complete the a’s) #’s 60, 62, 64, 66, 68, and question 78 Read 3.10 pgs. 114 -119 **

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