1. Just Follow the Recipe Introduction to Reaction Stoichiometry

2. Working with Recipes A recipe tells the “relative” amounts of various components A recipe tells the “relative” amounts of various components The amounts are given in prescribed units The amounts are given in prescribed units If you change the unit system you mess up the recipe If you change the unit system you mess up the recipe

3. Here’s a Recipe Chocolate chip cookies Chocolate chip cookies 3/4 cup sugar 3/4 cup packed brown sugar 1 cup butter, softened 2 large eggs,beaten 1 teaspoon vanilla extract 2 1/4 cups all-purpose flour 1 teaspoon baking soda 3/4 teaspoon salt 2 cups semisweet chocolate chips if desired, 1 cup chopped pecans 3/4 cup sugar 3/4 cup packed brown sugar 1 cup butter, softened 2 large eggs,beaten 1 teaspoon vanilla extract 2 1/4 cups all-purpose flour 1 teaspoon baking soda 3/4 teaspoon salt 2 cups semisweet chocolate chips if desired, 1 cup chopped pecans How do the amounts of sugar and brown sugar compare? If I used 3 cups of sugar how much brown sugar? How do the amounts of flour and sugar compare? If I used 3 cups of sugar how much flour do I need? What if I used 2 lbs of sugar?

4. How could I deal with the 2 lbs of sugar dilemma? The recipe calls for ¾ cup of sugar The recipe calls for ¾ cup of sugar To “work” the recipe we’ll have to convert lbs of sugar to cups To “work” the recipe we’ll have to convert lbs of sugar to cups A conversion factor (or definition) is needed A conversion factor (or definition) is needed Let’s say that 1 cup of sugar = 0.25 lb Let’s say that 1 cup of sugar = 0.25 lb Steps to follow: Convert 2 lbs to cups 2 lbs = X 0.25 lbs 1 cup X = 8 cups Work recipe 8 cups S = X 0.75cup S 2.25cup F X = 24 cups of flour

5. What Does It Mean to Follow the Recipe? The amounts must be measured in the units indicated by the recipe The amounts must be measured in the units indicated by the recipe The amounts must stay in the recipes proportion or ratio The amounts must stay in the recipes proportion or ratio You have to use the correct ingredients and conditions You have to use the correct ingredients and conditions

6. Let’s try an example with coins Given data regarding coin masses Given data regarding coin masses 1 doz Q = 68 g 1 doz Q = 68 g 1 doz D = 28 g 1 doz D = 28 g 1 doz N = 60 g 1 doz N = 60 g Given data regarding coin values (recipes) Given data regarding coin values (recipes) 1 doz Q = 2.5 doz D 1 doz Q = 2.5 doz D 1 doz Q = 5 doz N 1 doz Q = 5 doz N 1 doz D = 2 doz N 1 doz D = 2 doz N

7. Some examples of using recipes 969 grams of quarters are equal in value to what mass of dimes? 969 grams of quarters are equal in value to what mass of dimes? Steps: Steps: 1) convert mass of quarters to dozens of quarters. (Why?) 1) convert mass of quarters to dozens of quarters. (Why?) 2) Use the “recipe” of 2.5 doz D = 1 doz Q 2) Use the “recipe” of 2.5 doz D = 1 doz Q 3) Convert dozens of dimes to grams 3) Convert dozens of dimes to grams And, the answer is…. And, the answer is….

8. You try this one… 3060 grams of nickels have the same value as what mass of dimes? 3060 grams of nickels have the same value as what mass of dimes? Do the same three steps Do the same three steps Get into recipe units Get into recipe units Use recipe Use recipe Go back to measuring units Go back to measuring units And, the answer is… And, the answer is…

9. This same technique works for chemical reactions The recipe calls for number of atoms or molecules or ions The recipe calls for number of atoms or molecules or ionsnumber 2 Al + 3 CuCl 2  2 AlCl 3 + 3 Cu means 2 aluminum atoms for each 3 cupric chloride molecules 2 Al + 3 CuCl 2  2 AlCl 3 + 3 Cu means 2 aluminum atoms for each 3 cupric chloride molecules But, we measure in grams But, we measure in grams So, we use the mole because of its two meanings (see link above) So, we use the mole because of its two meanings (see link above)

10. A Chemistry Tale What mass of lead(II) phosphate can be made from 2.00 grams of sodium phosphate with excess lead(II)nitrate? What mass of lead(II) phosphate can be made from 2.00 grams of sodium phosphate with excess lead(II)nitrate? Reaction: Reaction: 3 Pb(NO 3 ) 2 (aq) + 2 Na 3 PO 4 (aq)  Pb 3 (PO 4 ) 2 + 6 NaNO 3 ( aq) 3 Pb(NO 3 ) 2 (aq) + 2 Na 3 PO 4 (aq)  Pb 3 (PO 4 ) 2 + 6 NaNO 3 ( aq) 2.00g (3)get grams 2.00g (3)get grams (1) find moles (2)find moles (1) find moles (2)find moles

11. Find moles 2.00 grams of sodium phosphate = ? moles 2.00 grams of sodium phosphate = ? moles 2.00 g = X 164 g 1 mol X = 0.01220 mol Na 3 PO 4 X = 0.01220 mol Na 3 PO 4

12. Relate mols of Na 3 PO 4 to mols of Pb 3 (PO 4 ) 2 1 Pb 3 (PO 4 ) 2 = X 2 Na 3 PO 4 0.01220 mols Na 3 PO 4 X = 0.006098 mols Pb 3 (PO 4 ) 2 X = 0.006098 mols Pb 3 (PO 4 ) 2

13. Moles back to grams 0.006098 mols Pb 3 (PO 4 ) 2 = X 0.006098 mols Pb 3 (PO 4 ) 2 = X 1 mol Pb 3 (PO 4 ) 2 811 g 1 mol Pb 3 (PO 4 ) 2 811 g X = 4.95 g X = 4.95 g