Percent Yield and Limiting Reagents - Oak Park USD

[Pages:12]Percent Yield and Limiting Reagents

February 17, 2015

Percent Yield

? Theoretical yield: the maximum amount of product, which is calculated using the balanced equation

? Actual yield: the amount of product obtained when the reaction takes place

Reasons for Percent Yield

? There are many reasons you might not get the expected amount of product from a reaction

? Sources of error, nature of rxn

? Percent Yield measures how much of the expected product you actually get

? If a package of chocolate chips is supposed to make 48 cookies, but you only make 34 cookies out of it, you didn't get 100% yield

Calculating Percent Yield

? Percent Yield Formula Measure it (given in problem)

percent yield = actual yield x 100 theoretical yield

Use Stoichiometry

Percent Yield Problem #1

? What is the percent yield of this reaction if 24.8 g of CaCO3 is heated to give 13.1 g of CaO?

CaCO3 ? CaO + CO2

? To find out how much product should be made:

? Set the problem up like you would a Mass-Mass Stoichiometry Problem

1. Balance The Equation 2. Convert Grams to Moles 3. Complete Mole Ratio 4. Convert Moles to Grams

? Then find % yield using the formula

Percent Yield Problem #1

? What is the percent yield of this reaction if 24.8 g of CaCO3 is heated to give 13.1 g of CaO? CaCO3 CaO + CO2 1. Balance The Equation: DONE

2. Convert Grams to Moles: 24.8 g CaCO3 = 0.247 Moles CaCO3 100.09 g CaCO3

3. Complete Mole Ratio:

CaCO3 = _1__ = 0.247 M CaCO3 = 0.247 M CaO

CaO 1

x M CaO

4. Convert Moles to Grams

theoretical

0.247 M CaO ? 56.08 g CaO = 13.9 g CaO

Percent Yield Problem #1

? What is the percent yield of this reaction if 24.8 g of CaCO3 is heated to give 13.1 g of CaO? CaCO3 CaO + CO2

13.1 g CaO is the ACTUAL YIELD (it's given in the problem!) 13.9 g CaO is the THEORETICAL YIELD (it's what you just

solved for)

? Now that you found out the theoretical value, plug your answer into the formula

percent yield = actual yield x 100 theoretical yield

percent yield = 13.1 g ? 100 = 94.2 % 13.9 g

Percent Yield Problem #2

? From the previous problem, the theoretical yield was calculated to be 152.6 g CaO. What would the actual yield be?

? Remember you calculated the % yield to be 94.2%

percent yield = actual yield x 100 theoretical yield

94.2% = actual yield ? 100 152.6 g

ACTUAL YIELD = 143.75 g

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