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Stoichiometry #3

Learn about stoichiometry and predicting product yield through a fun s'mores making experiment. Determine the limiting reactant and calculate the theoretical yield.

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Stoichiometry #3

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  1. Stoichiometry #3 October 22 & 23 2012 Ms. Boon Chemistry

  2. Objective: • Catalyst • The world’s largest s’more was built in 2006 at a state park in Virginia. • The s’more had 40,000 marshmallows. • The mass of 1 marshmallow is 0.6 grams. • Can you use the mass of a marshmallow to “count” 40,000 marshmallows without actually counting each one? How? I can use stoichiometry to predict the product yield of a chemical reaction. Agenda: • Catalyst • S’mores! • Notes: Limiting Reactant & Product Yield • Practice: Find the limiting reactant and yield • Exit Slip • HW: Read pp. 312-315 • Practice problems:p. 314 #1-3.

  3. Activity: S’Mores! In your notes: Balance the “equation” for making a s’more • Draw arrows labeling the reactants and products. • Is this a synthesis or decomposition reaction? __M + __C +__G  __MCG2 1 1 1 2

  4. S’mores - - continued Your table will receive a bag of s’more making supplies. Copy this data table into your notes. Count all your ingredients. Record your data. As a group, make as many s’mores as you can. You must use the balanced s’more equation. Record the # of s’mores you made. Send one person to record your table’s data on the board.

  5. S’mores Activity Wrap Up 1 M 1 C 2 G____ 1 MCG2 50 MCG2 X = 100 G 2 G____ 1 MCG2 100 G X 4 g/G = 400 g Answer the following questions in your notes. Which group made the most s’mores? Why? Which group made the least s’mores? Why? What is the ratio of marshmallows to chocolate in the balanced s’more equation? What is the ratio of graham crackers to s’mores in the balanced s’more equation? If you wanted to make 50 s’mores, how many graham crackers would you need? A graham cracker has a mass of 4 grams. What is the mass of graham crackers needed to make 50 s’mores?

  6. Mini Review – Last Week’s Exit Slip N2 + 3 H2 2 NH3 • What is the mole ratio of H2 to NH3? • How many moles of H2 are needed to produce 10 moles NH3? • How many moles H2 are needed to produce 170 grams NH3? (molar mass of NH3 is 17g/mol) • How many grams H2 are needed to produce 170 grams NH3? (NH3 =17g/mol; H2 = 2g/mol) 3molH2 2molNH3 3molH2 2molNH3 = 10mol NH3 X 15mol H2 170g NH3 10mol NH3 X 3molH2 2molNH3 ÷ = 17 g/mol = 15mol H2 3molH2 2molNH3 170g NH3 ÷ = 15mol H2 X 2 g/mol H2 17 g/mol = 10mol NH3 X = 30 g H2

  7. Notes: Limiting Reactant & Product Yield • Limiting reactant = the substance that controls the quantity of product that can form in a chemical reaction. • The limiting reactant runs out first. • Excess reactant = the substance that is not used up completely in a reaction. • Product Yield = the amount of product formed • Theoretical Yield = amount of product predicted from calculations. • Think, Pair, Share: • What was the limiting reactant in your group’s s’more experiment? • What were the excess reactants?

  8. Notes: Limiting Reactant & Product Yield • Example 1: s’mores! 1M + 1C + 2G → 1 MCG2 • You have 10 marshmallows, 10 chocolates and 15 grahams. How many s’mores can you make? What is the limiting reactant? • Step 1: Separate the question into two stoichiometry problems: • How many s’mores can you make from 10 marshmallows? • How many s’mores can you make from 15 graham crackers? • Step 2: Solve both problems. • Step 3: Compare your answers. The smaller answer has the limiting reactant.

  9. Notes: Limiting Reactant & Product Yield • Example 1: s’mores! 1M + 1C + 2G → 1 MCG2 • You have 10 marshmallows, 10 chocolates and 15 grahams. How many s’mores can you make? What is the limiting reactant? • How many s’mores can you make from 10 marshmallows? • How many s’mores can you make from 15 graham crackers?

  10. Notes: Limiting Reactant & Product Yield • Example 2: s’mores! 1M + 1C + 2G → 1 MCG2 • You have 6.0 g marshmallows, 60 g graham cracker, and excess chocolate. How many s’mores can you make? What is the limiting reactant? • 1 Marshmallow = 0.6 g 1 graham cracker = 4 g • Step 1: Separate the question into two stoichiometry problems: • How many s’mores can you make from 6.0 g marshmallow? • How many s’mores can you make from 60g graham cracker? • Step 2: Solve both problems. • Step 3: Compare your answers. The smaller answer has the limiting reactant.

  11. Notes: Limiting Reactant & Product Yield • Example 2: s’mores! 1M + 1C + 2G → 1 MCG2 • You have 6.0 g marshmallows, 60 g graham cracker, and excess chocolate. How many s’mores can you make? What is the limiting reactant? What is the yield? • 1 Marshmallow = 0.6 g 1 graham cracker = 4 g • How many s’mores can you make from 6.0 g marshmallow? • How many s’mores can you make from 60g graham cracker?

  12. Notes: Limiting Reactant & Product Yield • Example 3: Copper and Silver Nitrate Cu (s) + 2AgNO3 (aq) → 2Ag (s) + Cu(NO3)2 (aq) • Identify the limiting reactant and the theoretical (calculated) yield of silver (Ag) in grams, when 128 g Cu reacts with 170 g AgNO3 . • Step 1: Separate the question into two stoichiometry problems: • How many grams Ag will be produced from 128 g Cu? • How many grams Ag will be produced from 170 g AgNO3? • Step 2: Solve both problems. • Step 3: Compare your answers. The smaller answer has the limiting reactant and is the theoretical yield.

  13. Notes: Limiting Reactant & Product Yield • Example 3: Copper and Silver Nitrate Cu (s) + 2AgNO3 (aq) → 2Ag (s) + Cu(NO3)2 (aq) • Identify the limiting reactant and the theoretical (calculated) yield of silver (Ag) in grams, when 128 g Cu reacts with 170 g AgNO3 . • How many grams Ag will be produced from 128 g Cu? • How many grams Ag will be produced from 170 g AgNO3?

  14. Practice: Limiting Reactant & Product Yield • Show all your work on your own sheet of paper. • Pre-Lab Problems: Copper and Silver Nitrate Cu (s) + 2AgNO3 (aq) → 2Ag (s) + Cu(NO3)2 (aq) • Identify the limiting reactant and the theoretical (calculated) yield of silver (Ag) in grams, when 64 g Cu reacts with 170 g AgNO3 . • Identify the limiting reactant and the theoretical (calculated) yield of silver (Ag) in grams, when 6.4 g Cu reacts with 8.5 g AgNO3. • Identify the limiting reactant and the theoretical (calculated) yield of silver (Ag) in grams, when 32 g Cu reacts with 340 g AgNO3 . • Step 1: Separate the question into two stoichiometry problems: • Step 2: Solve both problems. • Step 3: Compare your answers. The smaller answer has the limiting reactant and is the theoretical yield.

  15. Exit Slip 3e • Copper and Silver Nitrate Single Displacement Reaction: Cu (s) + 2AgNO3 (aq) → 2Ag (s) + Cu(NO3)2 (aq) • What is the mole ratio of silver (Ag) to copper (Cu) in the balanced equation? • What is the mole ratio of silver (Ag) to silver nitrate (AgNO3) in the balanced equation? • How many grams Ag will be produced from 640 g Cu? • How many grams Ag will be produced from 1700 g AgNO3? • Identify the limiting reactant and the theoretical (calculated) yield of silver (Ag) in grams, when 640 g Cu reacts with 1700 g AgNO3 .

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