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Percent Yield: Theoretical vs. Actual Yield

Understand the concept of theoretical yield and actual yield in chemical reactions, calculate percent yield, and solve problems related to percent yield.

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Percent Yield: Theoretical vs. Actual Yield

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  1. Chapter 9 Percent Yield

  2. Theoretical Yield vs. Actual Yield • Theoretical yield is the amount of product we should produce from the complete conversion of a given amount of reactant to product • must be calculated • Actual yield is the amount of product that is actually formed during a reaction. • it is always less than theoretical yield because of incomplete reactions, impure reactants, side reactions, etc • must be given within the problem or measured during an experiment. • Theoretical yield is calculated from the amount of limiting reactant.

  3. Making Popcorn • If we started with 80 popcorn kernels and found only 72 of them popped. • What is the percent yield of popcorn?

  4. Percent Yield

  5. A reaction was supposed to make was 2.50 grams of Zn. You actually made 2.32 grams. What is the percent yield?

  6. 2Al + 3CuCl2 → 3Cu + 2AlCl3 • A chemistry student is trying to prepare copper metal by the reaction of aluminum with copper (II) chloride. →

  7. 2Al + 3CuCl2 → 3Cu + 2AlCl3 • If the student is able to prepare 3.67g of copper metal by the reaction of 1.27g of aluminum with excess copper (II) chloride. What is the percent yield?

  8. 6. Chromium (III) hydroxide will dissolve in concentrated sodium hydroxide according to the following equation: NaOH + Cr(OH)3 NaCr(OH)4 If you begin with 66.0g of Cr(OH)3 and obtain 38.4g of NaCr(OH)4, what is the percentage yield?

  9. Two other types of percent yield problems • In both these problems you will be given the percent yield. • Given the percent yield determine the amount of a product you can produce. • You make less. • Given the percent yield determine the amount of a reactant you need. • You use more.

  10. You make less • A bakery produces cookies at a percent yield of 92%. The bakers add enough ingredients to make 1525 cookies. How many cookies do they produce? 1525 (0.92) = 1403 cookies Multiply by the percent yield. “You make Less”

  11. You use more. • The same bakery (92% yield) has an order placed for 2150 cookies. The bakers will need to use enough ingredients for how many cookies. 2150 = 2337 cookies 0.92 Divide by percent yield. “You use more”

  12. 3. Ammonia is synthesized from hydrogen and nitrogen according to the following equation: N2 + 3H2 2NH3 If an excess of nitrogen is reacted with 3.41g of hydrogen, how many grams of ammonia can be produced assuming the reaction has a percentage yield of 48.8%?

  13. A chemical engineer needs to produce 212 g of zinc oxide by the process below: 2ZnS + 3O2 2ZnO + 2SO2 By doing trials runs he expects the process to run at a 78% yield. How much zinc sulfide should he use to prepare the 212 g of zinc oxide?

  14. Homework • Percentage Yield Worksheet

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