Post on 23-Dec-2015
PERCENT YIELDThis is used A LOT in ORGANIC CHEMISTRY
• Stoichiometry:• 1) Mole-Mole• 2)Mass-Mass• 3) Mass-Mole• 4) Mole-Mass
– All of the above are ONE step
• 1) Mass-# of Molecules• 2) # of Molecules-Mass
– These are TWO steps
• 1) Volume-Volume– This is THREE steps
• 1) Limiting and Excess Reagent– MANY steps…
PREVIOUS CONCEPTS AND CALCULATIONS
• It takes TIME.
• It takes STUDY TIME.
• It takes organization of each concept
• It takes meeting with me when you need help.
• It takes knowing the steps you need to take for each TYPE of calculation.
HOW CAN I KNOW ALL THIS?!?!
• In THEORY, when a teacher gives an exam, every student should make a 100%. Of course, this doesn’t happen.
• The performance of class is spread over a range of grades.
• Your grade is a RATIO of two items expressed as a PERCENTAGE.
• It compares how you performed to how you COULD HAVE performed.
• Example: There are a total of 50 points that can be scored. You make a score of 40. Your grade as a percentage is a ratio between what you made to what you could have made.
• 40/50 x 100% = 80%
PERCENT YIELD
• Percent Yield works the EXACT same way!
• Here is the general equation:
• Percent Yield= x 100%
• Theoretical Yield: Maximum amount of product that could be formed.
• Actual yield: Amount of product that is ACTUALLY formed.
• Percent Yield: The ratio between the two expressed as a percent (AKA Multiplied by 100)
PERCENT YIELD
• The actual yield is often LESS than the theoretical yield. Therefore, the percent yield is usually under 100%.
• It CANNOT be over 100%.• It usually will not be AT 100%.
• It just tells us the efficiency of the reaction or how WELL the reaction occurred.
PERCENT YIELD
• Impure reactants
• Side reactions that occur and form UNWANTED products
• Poor performance of lab procedure. Human Error. (Spilling, dropping, inaccurate measurements.)
WHAT CAUSES A PERCENT YIELD UNDER 100%
• Calcium Carbonate, which is found in seashells, is decomposed by heating. The balanced equation for this reaction is:
CaCO3 CaO + CO2
Part A: What is the THEORETICAL YIELD of CaO if 24.8 g CaCO3 is heated??
Part B: What is the PERCENT YIELD if 13.1g CaO is ACTUALLY produced?
EXAMPLE PROBLEM
1) When 84.8g of iron(III) oxide reacts, iron is produced.
Fe2O3 + 3CO 2Fe + 3CO2
a) What is the theoretical yield of iron?b) What is the percent yield of iron if 50 g of iron is actually produced?
2) Using the equation above, if 50.0g of Fe2O3 is reacted, you measured that 27g of CO2 was produced. What is the percent yield?
PRACTICE