1. Percent Yield

2. Why is it important?
Chemical reactions rarely produce the predicted amount of product.
Most rxns produce less than the expected amount of product
liquid reactants/products stick to glassware
evaporation
product is lost during purification
other unexpected products are formed (side products)

3. Actual versus Theoretical Yield
Theoretical yield: the calculated yield based on the balanced chemical equation
Actual yield: the amount actually produced when the reaction is carried out in an experiment
In the problem you will almost always be given the actual yield. This is the result of the experiment, so you don’t want to have to go complete an experiment to work a problem. If you are not given actual yield, then you must be given the percent yield and asked to find actual yield.

4. What does it tell me?
% yield is a measure of how efficient the reaction was

5. How to calculate % yield
% yield = actual (measured) yield/theoretical (predicted) yield
x 100

6. Determining % yield step 1: calculate the theoretical yield
step 2: measure the actual yield
step 3: actual/theoretical x 100

7. Example K2CrO4 + 2 AgNO3  Ag2CrO4 + 2 KNO3
If g AgNO3 was used and the actual yield of Ag2CrO4 was g, what is the percent yield?

8. Calculating % yield K2CrO4 + 2 AgNO3  Ag2CrO4 + 2 KNO3
step 1: calculate the theoretical yield:
determine the molar mass
AgNO3 = (16) = 169.9
Ag2CrO4 = 2(107.87) (16) = 331.7

9. Calculating % yield K2CrO4 + 2 AgNO3  Ag2CrO4 + 2 KNO3
step 1: calculate the theoretical yield
given g silver nitrate:
K2CrO AgNO3  Ag2CrO KNO3
0.500 g AgNO3 (331.7 g) (1 mol) Ag2CrO4
(169.9 g) (2 mol) AgNO3
(0.500) (331.7) (1) = g Ag2CrO4
(169.9) (2)

10. Calculating % yield step 2: measure the actual yield
0.455 g Ag2CrO4
step 3: actual/theoretical x 100
0.455 g Ag2CrO4 x 100
0.488 g Ag2CrO4
% yield = 93.2%

11. Importance of % Yield
A chemist must balance cost, % yield and the speed of the rxn to minimize cost and comply with environmental standards.