1. F LASHBACK In your notes … answer the following question to the best of your ability: 1.) How many atoms would there be in one mole? 2.) What would be the mass of one mole of Carbon atoms? 3.) What would be the mass of 2 moles of H 2 O?

2. T HE M OLE B Y : M S. B UROKER

3. W HAT IS THE M OLE ? The mole is the SI base unit used to measure the amount of a substance. * commonly abbreviated mol The mole can be defined as the number equal to the number of carbon atoms in 12.01 grams of carbon.

4. A VOGADRO ’ S N UMBER One mole of something consists of 6.022 x 10 23 units of that substance. 1 mol = 6.022 x 10 23 particles Molecules AtomsFormula Units (Ionic Compounds)

5. 1 mole of any element has a mass in grams that is equal to its average atomic mass Average atomic mass of this element 107.9 amu 207.2 amu Mass of this sample 107.9 g 207.2 g Number of atoms in this sample 6.022 x 10 23 atoms Silver (Ag)Lead (Pb)

6. M OLAR M ASS The molar mass of an element is the mass in grams of one mole of any pure substance. The molar mass of a compound or molecule is equal to the sum of the mass (in grams) of the elements involved. EXAMPLE: CHCl 3 C: 12.01g/mol H: 1.01g/mol Cl: 35.45g/mol x 3= 106.35g

7. M OLE R ELATIONSHIP AND C OMPOUNDS A chemical formulas tell us the number of atoms that make the compound … but, it can also tell us something about the number of moles of atoms in the compound! For example: CaCl 2 1 calcium atom In 1mol of CaCl 2, there is 1mol of calcium 2 chlorine atoms In 1mol of CaCl 2, there are 2moles of chlorine

8. L ET ’ S P RACTICE !! Determine the number of moles of chloride ions in 2.50mol ZnCl 2 5.00mol Cl - Calculate the number of moles of each element in 1.25mol glucose (C 6 H 12 O 6 ) 7.50mol C 15.0mol H 7.5mol O

9. S OME V OCABULARY … Percent Composition: The percent by mass of each element in a compound. Empirical Formula: The formula with the smallest whole number ratio of the elements. Molecular Formula: The formula which specifies the actual number of atoms of each element in one molecule or formula unit.

10. P ERCENT C OMPOSITION Mass of element Mass of compound X 100 = Percent by Mass Examples: Sodium hydrogen carbonate, also called baking soda, is an active ingredient in some antacids used for the relief of indigestion. Determine the percent composition of sodium hydrogen carbonate.

11. EMPIRICAL FORMULAS Empirical formulas may or may not be the same as the molecular formula … Example: Hydrogen peroxide empirical formula: HO molecular formula: H 2 O 2

12. H OW D O I F IND THE E MPIRICAL F ORMULA ? 1.)Find the number of moles of each element. * If given percent composition- assume 100.0g 2.) Calculate the simplest ratio of moles of the elements by dividing each number of moles by the smallest whole number ratio. * If the number are not whole, then multiply by the smallest number that will produce a ratio of whole numbers.

13. MOLECULAR FORMULAS Experimentally determined molar mass Mass of Empirical Formula n Multiply the numbers in the empirical formula by the value of “n” Molecular formula = (empirical formula) n =