Stoichiometry Loose Stoichiometry Loose Ends:Ends:

Limiting Reactants,Limiting Reactants,Percentage Yield, and Percentage Yield, and

Percentage ErrorPercentage Error

What is a What is a limiting reactantlimiting reactant??

The The substancesubstance that controls the that controls the quantity of quantity of productsproducts that can form in that can form in a chemical reaction.a chemical reaction.

In other words, the In other words, the reactantreactant that that limitslimits the reaction because you run the reaction because you run out of it.out of it.

Every other reactant is called the Every other reactant is called the excessexcess reactants. reactants.

How can we determine what is How can we determine what is going to be the limiting going to be the limiting

reactant?reactant? Convert Convert allall reactants into the same reactants into the same

product with the product with the samesame substance substance unit.unit.

The one that produces The one that produces lessless product is product is the the limitinglimiting reactant. reactant.

So, it is the same as before, but you So, it is the same as before, but you do it more than once.do it more than once.

Percentage YieldPercentage Yield

The The ratioratio of the experimental yield to of the experimental yield to the theoretical yieldthe theoretical yield

TheoreticalTheoretical yield – book value, yield – book value, “correct answer,” the calculated “correct answer,” the calculated value, value you were aiming at.value, value you were aiming at.

ExperimentalExperimental yield – measured value, yield – measured value, experimental value, value you got in experimental value, value you got in the labthe lab

FormulaFormula

Divide the Divide the experimentalexperimental value by the value by the theoreticaltheoretical yield and multiply by 100. yield and multiply by 100.

Experimental yieldExperimental yield

Theoretical yieldTheoretical yieldX 100

Percentage ErrorPercentage Error The margin of The margin of errorerror expressed as a expressed as a

percentpercent.. FormulaFormula

– Take the theoretical yield and Take the theoretical yield and subtractsubtract the experimental value. the experimental value.

– Divide this value by the Divide this value by the theoreticaltheoretical yield and multiply by 100%yield and multiply by 100%

Theoretical yield - Experimental yieldTheoretical yield - Experimental yield

Theoretical yieldTheoretical yield

X 100