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Moles Mole: A) B) C) D) A small blind burrowing furry rodent A spy A skin condition 6.02 x 10 23 Mole: A) B) C) D) A small blind burrowing furry rodent A spy A skin condition 6.02 x 10 23 6.02 x 10 23 is called Avogadro’s Number and a Mole This is COLLECTIVE NOUN What is the collective noun name for 12? A dozen Working with collective nouns • A Dozen is easy to work with because the number 12 is a small number. • • • • Two dozen = 2 x 12 = 24 A half dozen = 12/2 = 6 163.67 dozen = ???? 163.67 x 12 = 1964.04 (lots of eggs, or donuts or whatever…!) Working with collective nouns • A Mole is easy to work with because the number 6.02 x 10 23 is a number. • • • • Two moles = 2 x (6.02 x 10 23 )= 12.04 x 1023 A half mole = (6.02 x 10 23 )/2 = 3.01 x 1023 163.67 moles = ???? 163.67 x (6.02 x 10 23 ) = 985.3 x 1023 (lots and lots of eggs, or donuts or whatever…!) Review: Working with exponents 2 x (6.02 x 10 23 )= 12.04 x 1023 = 1.204 x 1024 163.67 x (6.02 x 10 23 ) = 985.3 x 1023 = 9.853 x 1025 Where did the Mole come from? A Mole is defined as the number of atoms of Carbon in 12.000 grams of carbon. (did somebody really count these out?) Why 12 grams of Carbon? Remember: The amu is based on Carbon-12 One carbon atom has a mass of 12 amu But who can work with one carbon atom??? Why 12 grams of Carbon? It just so happens that… One carbon atom has a mass of 12 amu One MOLE of carbons atoms has a mass of 12 grams Grams are easy to work with ! But this magic doesn’t just work for Carbon! The atomic mass (in grams) of any atom is the mass of one MOLE of that element The gram formula mass of any compound is the mass of one MOLE of that compound Since chemists are unbelievably lazy…. MOLE is often abbreviated as MOL Moles and GFM Since the gram formula mass is the mass of one mole, we can write this mathematically as: GFM = grams per mole = grams/mole = grams mole Moles and GFM So, for Na, with a GFM of 23 g There are 23 grams per mole of Na = 23 grams/mole = 23 grams mole Moles and GFM So, for NaCl, with a GFM of 58 g There are 58 grams per mole of NaCl = 58 grams/mole = 58 grams mole Converting grams to Moles This formula is in Table T; # of moles = given mass gram formula mass Converting grams to Moles # of moles = given mass gram formula mass How many moles of Na are in 333 g of Na? # of moles = 333g 23g/mole # of moles = 14.48 g/g/mole = 14.48 moles You try it! How many moles are there in 678 grams of NaCl? # of moles = 678 grams GFM # of moles = 678 grams NaCl 58.5 g/mol GFM of NaCl = 23 + 35.5 = 58.5g/mol = 11.6 mole NaCl Converting Moles to Grams This formula is NOT in Table T, but you can get it by rearranging the grams to mole formula Grams = # of moles x GFM Grams = # of moles x grams mole Converting Moles to Grams Grams = # of moles x GFM How many grams are there in 6.37 moles of Na? Grams = 6.37 moles x 23 grams Na mole Grams = 147 grams Na You try it! Grams = # of moles x GFM How many grams are there in 106.8 moles of NaCl? Grams = 106.8 moles x 58.5 grams/mol = 6248 grams NaCl Mole Relationships in chemical equations A recipe calls for: To make double the amount: 2 cups flour 4 eggs 1/2 cup chocolate chips 4 cups flour 8 eggs 1 cup chocolate chips Mole Relationships in chemical equations A recipe calls for: To make half the amount: 2 cups flour 4 eggs 1/2 cup chocolate chips 1 cups flour 2 eggs 1/4 cup chocolate chips You can write this as a chemical reaction (all cooking is!) 2 cups flour + 4 eggs + ½ cup chips 2 4 .5 1 cake 1 These numbers show the RATIOS of ingredients in the recipe that make it come out right If you know the correct ratios, you can double, triple or halve the recipe easily. 2 cups flour + 4 eggs + ½ cup chips 2 4 .5 1 cake 1 Suppose you only have 3 eggs ? How much flour will you need? 4 eggs (original recipe) 3 eggs (new recipe) = 2 cups flour (original recipe) X cups flour (new recipe) Cross multiply and solve for x 4X = 2x3 X= 6 4 X = 1.5 cups flour 2 cups flour + 4 eggs + ½ cup chips 2 4 .5 1 cake 1 Suppose you only have 3 eggs ? How many cups of chips will you need? 4 eggs (original recipe) 3 eggs (new recipe) = .5 cups chips (original recipe) X cups chips (new recipe) Cross multiply and solve for x 4X = .5 x 3 X = 1.5 4 X = .375 cups chips 2 cups flour + 4 eggs + ½ cup chips 2 4 .5 1 cake 1 Suppose you only have 3 eggs ? How many cakes can you make? 4 eggs (original recipe) 3 eggs (new recipe) = 1 cake (original recipe) X cakes (new recipe) Cross multiply and solve for x 4X = 1 x 3 X= 3 4 X = .75 cakes In balanced chemical equations.. the coefficients in front of the formulas can be interpreted two ways: as numbers of molecules (easy to visualize) Or As number of moles (practical in the lab) 4 NH3 + 5O2 4NO + 6H2O How many moles of water will be produced if 3 moles of ethane are burned? 2 C2H6 + 7 O2 2 7 4 CO2 + 6 H2O 4 6 (original) 3 ? ? 2 moles ethane (original) 3 moles ethane (new) 2X = 3 x 6 X = 18/2 = X (new) 6 moles water (original) X moles water (new) X = 9 moles water You try: How many moles of carbon dioxide will be produced? How many moles of oxygen gas will be needed?