Introduction to stocihiometry milestone

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Introduction to stocihiometry milestone

  1. 1. Stoichiometry Chemistry Chapter 9 Pg 237-261
  2. 2. Learning Goals Dy1  Objective:  We will calculate the amount of reactants required or products formed in a nonchemical process.  Product:  I will describe the relationship between the reactants and products using a real life, nonchemical process.
  3. 3. Agenda  Bell Ringer  Review prior learning  New learning What is Stoichiometry?  How does it relate to a recipe?  How can we use a balanced chemical reaction?   Product
  4. 4. Review Prior Learning  The Mole  Avogadro’s number  Molar Mass  Mole map
  5. 5. The Mole  A counting unit  Similar to a dozen, except instead of 12, it’s 602,000,000,000,000,000,000,000  6.02 X 1023 (in scientific notation)  This number is named in honor of Amedeo Avogadro (1776 – 1856)
  6. 6. Molar Mass  The Mass of 1 mole (in grams)  Equal to the numerical value of the average atomic mass (get from periodic table), or add the atoms together for a molecule 1 mole of C atoms = 1 mole of Mg atoms 1 mole of O2 molecules 12.0 g = = 32.0 g 24.3 g
  7. 7. Molar Mass of Compounds  The molar mass (MM) of a compound is determined the same way, except now you add up all the atomic masses for the molecule (or compound) Ex. Molar mass of CaCl2  Avg. Atomic mass of Calcium = 40.08g  Avg. Atomic mass of Chlorine = 35.45g  Molar Mass of calcium chloride = 40.08 g/mol Ca + (2 X 35.45) g/mol Cl  110.98 g/mol CaCl2  20 Ca 40.08 17 Cl 35.45
  8. 8. Atoms or Molecules Flowchart Divide by 6.02 X 1023 Multiply by 6.02 X 1023 Moles Multiply by atomic/molar mass from periodic table Divide by atomic/molar mass from periodic table Mass (grams)
  9. 9. Practice  Calculate the Molar Mass of calcium phosphate   Formula = Ca3(PO4)2 Masses elements:  Ca: 3 Ca’s X 40.1 =  P: 2 P’s X 31.0 =  O: 8 O’s X 16.0 = 120.3 g 62.0 g 128.0 g  Molar Mass = 120.3g + 62.0g +128.0g 310.3 g/mol
  10. 10. Calculations molar mass Grams Avogadro’s number Moles particles Everything must go through Moles!!!
  11. 11. Atoms/Molecules and Grams How many moles of Cu are present in 35.4 g of Cu? How many atoms? 35.4 g x 1 mol = 0.557 mol Cu 63.55 g 0.557 mol Cu x 6.02x1023 atoms = 3.35x1023 atoms 1 mol
  12. 12. On your own! How many moles of Fe are present in 102.4 g of Fe? How many atoms? 102.4 g x 1 mol = 1.83 mol Fe 55.85 g 1.83 mol Fe x 6.02x1023 atoms = 1.10x1024 atoms 1 mol
  13. 13. Work backwards! What is the mass (in grams) of 1.20x1024 molecules of glucose (C6H12O6)? 1.20x1024 molec. X 1 mol = 1.99 mol 6.02x1023 molec. 1.99 mol x 180.12 g = 358.4 g 1 mol From periodic table
  14. 14. Applying Stoichiometry to chemical equations Chapter 9 Pg 237
  15. 15. What is Stoichiometry?  Calculations of quantities in balanced chemical reactions.  Balanced Equations are recipes that tell chemists what amounts of reactants to mix and what amount of products to expect.  Let’s look at some recipes.
  16. 16. Chocolate Chip Cookies!! 1 cup butter 1/2 cup white sugar 1 cup packed brown sugar 1 teaspoon vanilla extract 2 eggs 2 1/2 cups all-purpose flour 1 teaspoon baking soda 1 teaspoon salt 2 cups semisweet chocolate chips Makes 3 dozen How many eggs are needed to make 3 dozen cookies? How much butter is needed for the amount of chocolate chips used? How many eggs would we need to make 9 dozen cookies? How much brown sugar would I need if I had 1 ½ cups white sugar?
  17. 17. Cookies and Chemistry  Just like chocolate chip cookies have recipes, chemists have recipes as well  Instead of calling them recipes, we call them reaction equations  Furthermore, instead of using cups and teaspoons, we use moles  Lastly, instead of eggs, butter, sugar, etc. we use chemical compounds as ingredients
  18. 18. Guided Practice  In a 5 day workweek, Tiny Tyke is scheduled to make 640 tricycles. How many wheels should be in the plant on Monday morning to make these tricycles?  Use the equation recipe on page 238.  F+S+3W+H+2P FSW3HP2  F- frame S-seat W-wheels H-handlebars P- pedals
  19. 19. Guided Example  Your group has been selected to prepare a cake for the class bake sale. You can calculate the number of cakes that you can make from the ingredients you have by using the recipe.
  20. 20.  Write the “Cake Equation”  4cupsflour + 1 stick butter + 4 eggs + 4cups sugar + 3 cups milk + 1 spoon baking powder = 1 cake  You have these ingredients:  5 cups of flour,6 cups of sugar,6 eggs, 6 cups of milk, a lot of baking powder, 3 sticks of butter
  21. 21. Closure  Stoichiometry will include conversions between different substances and amounts indicating how much are necessary for a given reaction.  A chemical equation is similar to a recipe.  The amount of product made depends on the amount of reactants available.
  22. 22. Product  Summarize the relationship between the reactants and products using a real life, nonchemical process such as making a circuit work.
  23. 23. Mole to Mole conversions ( dy2)  We will construct mole ratios and use them to solve problems  I will describe the relationship between the reactants and products using mole ratios.
  24. 24. Interesting Facts  Ratio of  Ratio of  Ratio of
  25. 25. What is a RATIO?  In math………….  What does it tell you?  How can it be written?
  26. 26. What information can we get?  From a balanced equation:  N2 + 3H2  2NH3  Moles?  Note: Coefficient in a balanced equation tells us the number of moles.
  27. 27. Chemistry Recipes  Looking at a reaction tells us how much of something you need to react with something else to get a product (like the cookie recipe)  Be sure you have a balanced reaction before you start!    Example: 2 Na + Cl2  2 NaCl This reaction tells us that by mixing 2 moles of sodium with 1 mole of chlorine we will get 2 moles of sodium chloride What if we wanted 4 moles of NaCl? 10 moles? 50 moles?
  28. 28. Practice  Write the balanced reaction for hydrogen gas reacting with oxygen gas. 2 H2 + O2  2 H2O 2 mol H2 How many moles of reactants are needed? 1 mol O2  What if we wanted 4 moles of water? 4 mol H2 2 mol O2   What if we had 3 moles of oxygen, how much hydrogen would we need to react and how much water would we get? 6 mol H2, 6 mol H2O  What if we had 50 moles of hydrogen, how much oxygen would we need and how much water produced? 25 mol O2, 50 mol H2O
  29. 29. Mole Ratios  These mole ratios can be used to calculate the moles of one chemical from the given amount of a different chemical  Example: How many moles of chlorine is needed to react with 5 moles of sodium (without any sodium left over)? 2 Na + Cl2  2 NaCl 5 moles Na 1 mol Cl2 2 mol Na = 2.5 moles Cl2
  30. 30. Mole-Mole Conversions  How many moles of sodium chloride will be produced if you react 2.6 moles of chlorine gas with an excess (more than you need) of sodium metal? 2 Na + Cl2  2 NaCl 2.6 moles Cl2 2 mol NaCl 1 mol Cl2 = 5.2 moles NaCl
  31. 31. Mole-Mass Conversions  Most of the time in chemistry, the amounts are given in grams instead of moles  We still go through moles and use the mole ratio, but now we also use molar mass to get to grams  Example: How many grams of chlorine are required to react completely with 5.00 moles of sodium to produce sodium chloride? 2 Na + Cl2  2 NaCl 5.00 moles Na 1 mol Cl2 2 mol Na 70.90g Cl2 1 mol Cl = 177g Cl2
  32. 32. You Practice  Calculate the mass in grams of Iodine required to react completely with 0.50 moles of aluminum. 2 Al + 3 I2  2 AlI3
  33. 33. Mass-Mole  We can also start with mass and convert to moles of product or another reactant  We use molar mass and the mole ratio to get to moles of the compound of interest Calculate the number of moles of ethane (C2H6) needed to produce 10.0 g of water  2 C2H6 + 7 O2  4 CO2 + 6 H20  10.0 g H2O 1 mol H2O 2 mol C2H6 = 0.185 18.0 g H2O 6 mol H20 mol C2H6
  34. 34. Mass-Mass Conversions  Most often we are given a starting mass and want to find out the mass of a product we will get (called theoretical yield) or how much of another reactant we need to completely react with it (no leftover ingredients!)  Now we must go from grams to moles, mole ratio, and back to grams of compound we are interested in
  35. 35. Mass-Mass Conversion  Ex. Calculate how many grams of ammonia are produced when you react 2.00g of nitrogen with excess hydrogen.  N2 + 3 H2  2 NH3 2.00g N2 1 mol N2 2 mol NH3 17.06g NH3 28.02g N2 1 mol N2 = 2.4 g NH3 1 mol NH3
  36. 36. Practice  How many grams of calcium nitride are produced when 2.00 g of calcium reacts with an excess of nitrogen?

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