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