Percent Yield

Section 12.3

Percent Yield

Often when reactions are actually carried out in the lab, there is a difference between the amount of product we expect and the amount we actually get. Side reactions take place that we can’t control Impure reactants Loss of product due to transfers Errors in measuring reactants or products Impurities in products (ex - dirty glassware)

Terms

Theoretical Yield – maximum amount of product that could be formed from the amounts of reactants given Calculated number

Actual Yield – the actual amount of product made when the reaction is carried out in a lab Experimental number

Percent Yield – ratio of the actual yield to the theoretical yield expressed as a percentage almost always less than 100%

Equation and Steps

100% yieldtheortical

yieldactual yield%

Steps:

1.Find theoretical yield by solving a basic stoichiometry problem using the amount of reactant given (usually 3-step problem)

2.Calculate percent yield using value from #1 and amount of product given in the problem.

Example Problems

1. When 84.8 g of iron(III) oxide reacts with an excess of carbon monoxide, 54.3 g of iron are produced. What is the percent yield?

Fe2O3 + 3 CO → 2 Fe + 3 CO2

2. Lead nitrate can be decomposed by heating. What is the percent yield of the decomposition reaction if 9.9 g Pb(NO3)2 are heated to give 5.5 g of PbO?

2 Pb(NO3)2 → 2PbO + 4NO2 + O2

Work with your partner

3. In a particular reaction between copper metal and silver nitrate, 12.7 g Cu produced 38.1 g Ag. What is the percent yield of silver in this reaction?

Cu + 2 AgNO3 → Cu(NO3)2 + 2 Ag