1. Percent Yield
in a
Chemical Reaction

2. Sometimes all the product in a chemical reaction is not produced.
Percent Yield
Sometimes all the product in a chemical reaction is not produced.
Some of the reactant might produce other products or some of the reactants might be spilled when transferred from the balance to the test tube or beaker.

3. Chemists are interested in the efficiency of the reaction.
The efficiency is measured by comparing the actual yield to the theoretical yield.

4. Actual yield = the amount of product produced by actually performing the reaction in lab and measuring its mass.
Theoretical yield = the amount of product that should be produced based on a stoichiometry calculation.

5. Stoichiometry Problem
Zn HCl a ZnCl2 + H2
A lab group dropped 6.5 g of zinc into a test tube containing hydrochloric acid (HCl). After the reaction was over they measured 12 g of ZnCl2 produced by this reaction.
What is the theoretical yield?
What is the percent yield?

6. Zn + 2 HCl a ZnCl2 + H2 6.5 g 12 g What is the theoretical yield?
Stoichiometry Problem
Zn HCl a ZnCl2 + H2
6.5 g
12 g
What is the theoretical yield?
1 mol Zn
136
g ZnCl2 1
mol ZnCl2
6.5 g Zn x
___________ x
____________ x
____________ =
13.6 g ZnCl2
65 g Zn 1
mol ZnCl2 1
mol Zn

7. Zn + 2 HCl a ZnCl2 + H2 6.5 g 12 g = actual yield
Stoichiometry Problem
Zn HCl a ZnCl2 + H2
6.5 g
12 g
= actual yield
13.6 = theoretical yield
____________ x
mol Zn
mol ZnCl2
___________
65 g Zn
1 mol Zn
6.5 g Zn
g ZnCl2 1
136 =
13.6 g ZnCl2

8. Zn + 2 HCl a ZnCl2 + H2 6.5 g 12 g = actual yield
Stoichiometry Problem
Zn HCl a ZnCl2 + H2
6.5 g
12 g
= actual yield
13.6 g = theoretical yield
What is the percent yield?
12 g
= 88 %
% yield =
X 100
13.6 g

9. Another lab group burned 3. 0 g of magnesium and collected 4
Another lab group burned 3.0 g of magnesium and collected 4.2 g of MgO.
What is their percent yield?
2 Mg + O2 a 2 MgO
3.0 g
4.2 g
4.2 g
% yield =
X 100
theoretical yield

10. 2 Mg + O2 a 2 MgO 4.2 g = actual yield 5.0 g = theoretical yield
0.125 mole
5.0 g = theoretical yield
0.125 mole
Theoretical yield:
1 mol Mg 40
g MgO 2
mol MgO
3.0 g Mg x
___________ x
____________ x
____________
= 5.0 g MgO
24 g Mg 1
mol MgO 2
mol Mg
actual yield
4.2 g
= 84 %
% yield =
X 100 =
X 100
theoretical yield
5.0 g