PERCENT YIELD This 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

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: CaCO 3  CaO + CO 2 Part A: What is the THEORETICAL YIELD of CaO if 24.8 g CaCO 3 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. Fe 2 O 3 + 3CO  2Fe + 3CO 2 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 Fe 2 O 3 is reacted, you measured that 27g of CO 2 was produced. What is the percent yield? PRACTICE