 How many atoms are in 3.6 mol of calcium?  How many moles are in 1.45 x atoms of sodium?  What is the molar mass of K 2 SO 4 ?  How many grams of CO are in 2.9 moles?  How many moles is 236 g of NaOH?  What is the mass of 7.6 x atoms of KF?  How many atoms are in 192 g of MgCl 2 ?

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 Formulas tell us ratios of the number of atoms in the compound  Ex. Freon is CCl 2 F 2  There is 1 C, 2 Cl, and 2 F  We can figure out how many moles of one element there are in a given compound.  Moles of compound x # of atoms of element 1 mole of compound

 How many moles of F are in 5.50 moles of CCl 2 F 2 ?  Calculate the number of moles of each element in 1.25 moles of C 6 H 12 O 6.

 First, find the molar mass of the compound  Multiply the mass of one element by its subscript  Divide the mass of one element by the total mass in the compound  Multiply by 100  Ex. H 2 O

 Determine the percent by mass of each element in the compound CaCl 2.

 Calculate the percent composition of each of the following element in the compound Ga 2 (SO 4 ) 3.  If you have a 100g sample of MgO and 60% is magnesium and 40% is oxygen, how many grams of each do you have?

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 Empirical formula = the formula with the smallest whole number ratio of the elements  If you know the percent composition of the element, divide the amount of that element by its molar mass.  This tells you # moles of that element.  If it is written as a percent, assume there are 100 g of the compound  If the numbers aren’t whole numbers, divide by the smaller value  If the numbers still aren’t whole numbers, multiply by the smallest factor that will make them whole

 Compound with 40.05% S and 59.95% O  Determine the empirical formula for methyl acetate which has the following chemical make up: 48.64% C, 8.16% H, and 43.20% O.

 Sometimes the empirical formula is the same for two different compounds  When that happens, you take the experimentally determined molar mass of the compound and divide it by the mass of the empirical formula  This gives you a whole number (n) that must be multiplied into the empirical formula

 Succinic acid is composed of 40.68% C, 5.08% H and 54.24% oxygen and has a molar mass of g/mol. Determine the empirical and molecular formulas for succinic acid.