Section 2: Mass and the Mole Which one weighs more? Why? Same number different masses Same concept in chemistry… 1 mole = 6.022 x 1023 atoms (single element) But… atoms are not all the same size. That is why… 1 mol of carbon atoms = 12 g C (Periodic Table) 1 mol of iron atoms = 55.85 g Fe (Periodic Table) Same number…different mass

Calculating Moles and Mass 1 mol of element = atomic mass of element 1 mol of compound = formula or molar mass of compound Example 1 mol of Fe = 55.847 g 1 mol of Na = 22.990 g 1 mol of carbonic acid (H2CO3) = 62.024 g (Add Them Together!) 1 mol of sodium chloride (NaCl) = 58.443 g (Add Them Together!)

Example Calculate the formula mass for ammonia (NH3) Step 1 Write down the different elements and their atomic mass N 14.007g H 1.008g Step 2 Count how many of each element is present and multiply the quantity by the atomic mass N 14.007g x 1 H 1.008g x 3 = 14.007 g = 3.024 g Step 3 Add all the totals together Formula mass = 14.007 + 3.024 = 17.031 g

Solving the problems Using the Tools 1st…Follow your rules. 1. What do I know? 2. What do I want? 3. How do I get there?(Tools) You have 2 tools in your tool box! 1 mol Al 6.022 x 1023 particles Al Avogadro’s # 1 mol Al 107.87g of Ag 107.87g of Al Molar Mass

PRACTICE USING THE TOOLS Example: Determine the mass in grams of 3.57 mol Al Follow your rules… 1. What do I know? 2. What do I want? 3. How do I get there?(Tools) 3.57 mols of Al “Given” = g of Al 9.63 1 mol Al 6.022 x 1023 particles Al 6.022 x 1023 particles Al 1 mol Al 1 mol Al 26.98 g of Al 26.98 g of Al 1 mol Al

PRACTICE USING THE TOOLS Example: Determine the number of moles 25.5 grams Ag. Follow your rules… 1. What do I know? 2. What do I want? 3. How do I get there?(Tools) 25.5 g of Ag “Given” = mols of Ag 0.236 1 mol Al 6.022 x 1023 particles Al 6.022 x 1023 particles Al 1 mol Al 1 mol Al 107.87g of Ag 107.87g of Al 1 mol Al

Example How many mols of oxygen are in 52 g of oxygen - - - 1 mol O2 x = 1.625 mol O2 = 1.6 mol O2 31.998 g O2 - - - Example How many mols of calcium are in 37 g of calcium 37 g Ca - - - - 1 mol Ca x = 0.92 mol Ca = 0.9232 mol Ca 40.08 g Ca - - - - Example How many mols of sodium chloride are in 100 g NaCl 100 g NaCl - - - - - 1 mol NaCl x = 2 mol NaCl = 1.711 mol NaCl 58.443 g NaCl - - - - -

Example How many grams of hydrogen are in 1.67 mol of hydrogen 1.67 mol H2 - - - - - 2.016 g H2 x = 3.367 g H2 = 3.37 g H2 1 mol H2 - - - - Example How many grams of carbon are in 0.85 mol of carbon 0.85 mol C - - - - 12.011 g C x = 10. g C = 10.209 g C 1 mol C - - - - Example How many grams of ammonia are in 2.3 x 105 mol ammonia 2.3 x 105 mol NH3 - - - - - - 17.031 g NH3 x = 3.917 x 106 g NH3 = 3.9 x 106 g NH3 1 mol NH3 - - - - -

Converting Mass and atoms Golden Rule…GET TO MOLES!!!! Then you can do what ever you want! Mass (g) Moles (mol) Particles Example: How many atoms are in 55.2 g Li 55.2 g of Li “Given” = mols of Li 7.95 = atoms of Li 4.79 x 1024 1 mol Li 6.022 x 1023 particles Li 6.022 x 1023 particles Li 1 mol Li 1 mol Li 6.94 g of Li 6.94 g of Li 1 mol Li 9

Example. An extra strength aspirin tablet contains Example An extra strength aspirin tablet contains 0.500g of aspirin (C9H8O4). How many molecules of aspirin are in one tablet - - - - - - - - 0.500 g C9H8O4 1 mol C9H8O4 - - - - - - - 6.022 x 1023 molecules C9H8O4 x x - - - - - - - 180.16171 g C9H8O4 - - - - - - - - 1 mol C9H8O4 = 1.67 x 1021 molecules C9H8O4 = 1.671 x 1021 molecules C9H8O4 Example In a small firework, 3.467 x 1022 atoms Sr are used to make the firework burn red. How many grams of strontium are in the firework. 3.467 x 1022 atoms Sr 1 mol Sr - - - - - - - - - - - - 87.620 g Sr x x = 5.044 g Sr 1 mol Sr - - - - 6.022 x 1023 atoms Sr - - - - - - -