Warm-up 5.11
• S’MORES FACTORY
• One afternoon you return home and decide to make s’mores
for yourself and friends. To make 1 s’more you need 4
graham crackers, 1 marshmallow, & 2 chocolate squares. In
the pantry you find 20 whole graham cracker (4 squares each),
an entire bag of marshmallows (100+) and 3 chocolate bars (8
pieces each). How many s’mores can you make? Why can’t
you make more? Which part limited how many you could
make?
•
Limiting Reactant
• LIMITING REACTANTS
• A. The reactant that produces the least amount of product is theLimiting Reactant
• B. The reactant that is not completely used up is in- Excess
• C. Determining the limiting reactant:
•
Step 1- Write the Balanced equation
•
Step 2- Calculate the mass of one of the products using
the masses given for each reactant (2 problems)
•
Step 3- Determine which produces the smaller amount of
product= Limiting Reactant
Example 1
• Some rocket engines use a mixture of hydrazine, N2H4 and hydrogen
peroxide H202 as the propellant. The products are nitrogen gas and
water vapor. What is the limiting reactant if 0.750 moles of
hydrazine is mixed with 0.500 moles of hydrogen peroxide?
• Step 1- Write the balance equation
•
Step 2- Calculate mass of one of the products (pick the
simplest) 2 problems
• Which is the limiting reactant? ______________________
• Which is in excess?_______________________________
• How much product will be produced?___________________
Example 2
• Aspirin (C9H8O4) is synthesized by the reaction of salicylic acid
(C7H6O3) with acetic anhydride (C4H6O3). Water is the other
product. When 20.0 grams of salicylic acid and 20.0 grams of the
anhydride react which is the limiting reactant?
• Which is the limiting reactant? ______________________
• Which is in excess?_______________________________
• How much product will be produced?___________________
Percent Yield
• Rarely in a chemical reaction will you get 100% of your product(s).
Things often “go wrong” or get messed up. Even without errors
product often “get lost” in equipment or evaporates before it can be
collected.
•
• Theoretical Yield - When Stoichiometry is used to calculate the
amount of products that should be formed from the reactants.
•
• Actual Yield- The amount of product that is actually formed in the
lab. Usually less
• Percent Yield- what percentage of the actual
amount obtained compared to the
theoretical amount
•
• Actual Yield
x 100 = % Yeild
• Theoretical Yield
• ***Memorize this formula!!!!!!!!!!!
• Example: A piece of Copper with a mass of 5.00 g is placed in a
AgNO3 solution in excess. The silver metal produced has a mass of
15.2 g. What is the percent yield?
•
• Step 1- Write Balance Equation
•
•
• Step 2- Calculate the Theoretical Yield
• Step 3- Calculate % Yield