Limiting Reactant and Percent Yield Lab
Objectives:
Learn to determine the limiting reagent of a reaction.
Learn how to calculate theoretical, actual, and percent yield of a reaction.
Background:
During a chemical reaction when two substances react, often times one reactant will
be consumed before the other. The substance that is consumed first is called the
limiting reactant. This is the substance that controls or limits the amount of
products formed.
Think about it in terms of making grilled cheese. If to make one grilled cheese it
takes two pieces of bread and one piece of cheese and you have four pieces of bread
and one piece of cheese how many sandwiches can you make? The answer is one
and therefore the cheese would be considered the limiting reactant. The two other
slices of bread would be left unused and considered the excess reactant.
The limiting reactant for a specific reaction can be determined by calculating the
amount of product that each reactant can produce. The reactant that forms the
least amount of product will be the limiting reactant. The amount of product
formed by the limiting reactant is the theoretical yield of the reaction.
The theoretical yield of a chemical reaction is the maximum amount of product that
can be formed if the reaction proceeds perfectly. However, not all reactions proceed
perfectly. Sometimes not all of the limiting reactant is used up or some of the
product can be lost during collection. The amount recovered from the reaction is
known as the actual yield. The ratio of the actual yield to the theoretical yield is
known as the percent yield and can be calculated using the formula below.
Percent yield = (actual yield/theoretical yield) x 100
Pre-lab Questions:
1. Write the balanced reaction of Al with CuCl2.
2. What is the limiting reactant if 0.5 g Al is reacted with 3.5 g CuCl2? Take into
account CuCl2 is a dihydrate when calculating the molecular weight.
