Class Lab #
Name: ________________________________
Lab Title: Limiting Reactant & Percent Yield
Date Performed: ________________________
PURPOSE:
Students will determine the theoretical, actual and percent yield of a chemical equation by
conducting an experiment.
INTRODUCTION
The limiting reagent, also known as the "limiting reactant", is the chemical that
determines how far the reaction will go before the chemical in question gets
"used up", causing the reaction to stop. The chemical of which there are fewer
moles than the proportion requires is the limiting reagent.
The Excess Reactant is the reactant in a chemical reaction that remains when a
reaction stops when the limiting reactant is completely consumed. The excess
reactant remains because there is nothing with which it can react.
In chemistry, yield, also referred to as chemical yield and reaction yield, is the
amount of product obtained in a chemical reaction.
The theoretical yield is what is expected from the chemical equation
before running the actual laboratory procedure. This is obtained through
stoichiometric calculations.
Reactions rarely produce the predicted amount of product from the
masses of reactants in the reaction. The actual yield is the amount of
product actually produced and measured during a reaction.
The percent yield is a measure the effectiveness of a chemical reaction,
and is calculated by dividing the amount of the obtained product (actual
yield) in moles by the theoretical yield.
The ideal or theoretical yield of a chemical reaction would be 100%, a value that is impossible to achieve due to
limitations in measurement accuracy.
HYPOTHESIS:
Determine the theoretical yield of copper produced from the mass of iron used in the
replacement reaction of iron plus copper sulfate (CuSO4). (analysis 1 & 2) Write your
hypothesis in terms of an if/then statement.
MATERIALS:
Approximately 1-2 grams of Iron filings
Approximately 10-12 grams of copper sulfate (CuSO4)
250-mL beaker
wash bottle containing distilled water
centigram or electronic balance
weighing boat
Stirring rod
Larger disposal beaker
PROCEDURE:
Part 1: Reacting the chemicals
1) Measure and record the mass of a clean, dry 250-mL beaker.
2) Place approximately 50-mL (10 g) of copper (II) sulfate pentahydrate (CuSO4 5H20) into the 250-mL beaker
and measure and record the combined mass.
3) Measure approximately 1-2 g of iron (Fe) metal filings onto the piece of weighing paper or weighing boat.
Measure and record the exact mass of the iron powder.
4) While stirring the copper sulfate solution with the stirring rod, slowly add the iron filings to the copper (II)
sulfate solution. Do not add all the iron powder at once. Continue to stir.
5) Allow the reaction mixture to stand, without stirring, for about five minutes to ensure complete reaction.
The solid copper metal will settle to the bottom of the beaker. If small iron powder is still floating, use a
small amount of soap dish to make the filings settle to the bottom.
Part 2: Collecting the copper
6) Use the stirring rod to decant (pour off) the liquid slowly into a larger disposal beaker or container. Be
careful to decant only the liquid.
7) Add about 15-mL of distilled water to the copper solid and carefully swirl the beaker to wash the copper.
Decant the liquid slowly and carefully into the disposal beaker.
8) Repeat step 7 two more times.
9) Place a label on your beaker to sit for the weekend.
10) Place the 250-mL beaker containing the wet copper carefully on the hot plate. Use low heat to dry the
copper. Do not overheat the wet copper.
11) Once there is no signs of water vapor on the beaker, remove the beaker from the hot plate using tongs and
allow it to cool.
12) Measure and record the exact mass of the cooled 250-mL beaker and copper
Cleanup and Disposal:
13) Make sure the hot plate is off.
14) The dry copper can be placed in a waste container. Wet any residue that sticks to the beaker and wipe it out
using a paper towel. Pour the un-reacted copper (II) sulfate and iron (II) sulfate solutions into a large beaker
in the fume hood.
15) Put all lab equipment to its proper place.
16) Wash your hands thoroughly after all lab work and clean up is complete.
Manipulated Variable:
The manipulated variable in this lab is iron because iron will be used to replace the copper in the copper sulfate
solution.
Responding Variable:
The responding variable will be copper because it is going to be affected by the amount of iron used in the
experiment.
DATA TABLE:
Mass of empty 250-mL beaker
Mass of CuSO4
Mass of iron powder
Mass of 250-mL beaker & dried copper
Mass of dried copper (actual yield)
DATA ANALYSIS:
1) Convert the grams of iron used and copper recovered into moles of each.
2) Compare the molar ratio obtained to the molar ratio in the balanced chemical equation.
3) Determine the theoretical yield of the copper using the limiting reactant concept.
4) Use your actual and theoretical yields to determine your percent yield.
ASSIGNED QUESTIONS
1) What evidence did you witness to explain that there was a chemical reaction that took place between CuSO4
and Fe?
2) Did you produce the exact amount of copper metal expected? Why not?
3) Give one reason why all of the copper did not get replaced by the iron.
4) What are some possible sources of error in this experiment?
http://www.scribd.com/doc/32408222/Iron-Copper-Single-Replacement-Reaction