Unit 8: Percent Yield Calculations

Formula for Percent Yield:

• Percent yield = Actual (also called Experimental yield) Theoretical Yield X 100

• Actual (Experimental) yield: What was actually produced in the reaction. This is given to you in the problem. It is not placed into the BCA chart.

• Theoretical yield: What should have been produced in the reaction.– What we have been calculating to this point (i.e. on

worksheets 8.1 and 8.15) has been theoretical yield. We just have not been referring to our answers with this term.

Example

#4 on Unit 8.2 Suppose 4.61 g of zinc was allowed to react with hydrochloric acid to

produce zinc chloride and hydrogen gas. How much zinc chloride should you get? Suppose that you actually recovered 8.56 g of zinc chloride. What is your percent yield?

Balanced Equation: Zn + 2HCl ZnCl2 + H2

Before Change

After

First convert grams of Zinc to moles:

4.61 g Zn 1.00 mol Zn 1 65.4 g of Zn

X = .0705 mol Zn

Complete the BCA

Balanced Equation: Zn + 2HCl ZnCl2 + H2

Before 0.0705 xs 0 0

Change -0.0705 -0.141 +0.0705 +0.0705

After 0 xs 0.0705 0.0705

Calculate Theoretical Yield:

• The BCA amounts calculated are “theoretical” values based off of the given reactant value.

• Convert the moles of zinc chloride to grams. You do this due to being given a gram amount of the product (actual yield).

0.0705mol ZnCl2 136.3 g of ZnCl2

1 1.00 mol ZnCl2

X = 9.61 g Zn

Calculate Percent Yield:

8.56 g ZnCl2 (Experimental yield…given)

9.61 g ZnCl2 (Theoretical yield…calculated)

This is your final answer to Problem #4

X 100 = 89.1%