Unit VII: Stoichiometry
Determination of the Formula for an Iron Compound Using Stoichiometry
Learning Targets: 3, 4, 5 & 6
Problem
What is the formula for the iron-containing compound formed when copper (II) sulfate reacts
with pure iron?
Introduction
We learned in Chapter 4 that iron can form more than one type of ion. The possible reactions are:
copper(II) sulfate(aq) + iron(s) → copper(s) + iron(II) sulfate(aq)
copper(II) sulfate(aq) + iron(s) → copper(s) + iron(III) sulfate(aq)
In this lab you will measure the amount of product formed when measured amounts of reactants
are mixed. From this information, you will determine which equation applies to the reaction you
run in this experiment.
Prelaboratory Assignment
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Read the entire experiment before you begin.
Answer the Prelaboratory Questions.
1. Write out and balance each of the following equations (given in the Introduction).
2. If iron(III) sulfate were formed, what mass of copper would be expected?
3. If iron(II) sulfate were formed, what mass of copper would be expected?
Materials
Apparatus
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Safety goggles
Lab apron
Two 250-mL beakers
Ring stand
Ring
Wire Gauze
Bunsen burner
Balance
Stirring rod
Matches
Reagents
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Copper(II) sulfate (anhydrous)
Water
Safety
1. Safety goggles and a lab apron must be worn at all times in the laboratory.
2. If you come in contact with any solution, wash the contacted area thoroughly.
3. You will work with a flame in this lab. Tie back hair and loose clothing.
4. Do not drop matches into the sink. Dispose of burned matches in the trash can after they are
cool.
Procedure
1. Place 7.00 g of copper(II) sulfate in a beaker.
2. Add about 50 mL of water to the beaker.
3. Arrange the beaker and ring stand as shown in Figure 1.
Figure 1
Apparatus to heat a solution
4. Light the Bunsen burner and place it under the beaker. Adjust the burner so the hottest part of
the flame touches the bottom of the beaker.
5. Carefully heat and stir the mixture in the beaker. The solution should be hot, but not boiling.
After all of the crystals have dissolved, remove the beaker from the heat.
6. Add 2.00 g of iron filings slowly to the hot copper sulfate solution while stirring. Record
observations.
7. Allow the beaker to cool for 10-15 minutes.
8. Pour off (decant) the solution into a different beaker. Pouring the solution down a stirring rod
is recommended. Make sure not to disturb the copper in the beaker.
9. Add a small amount of water (10 to 15 mL) to the copper and stir.
10. Let the copper settle to the bottom of the beaker and decant again.
11. Dry the copper as your teacher directs and determine its mass. Record this mass.
Cleaning Up
1. Place the copper in the waste container provided by your teacher.
2. Place the remaining solution in the labeled container.
3. Wash all glassware and return all materials to the proper locations.
4. Wash your hands thoroughly before leaving the laboratory.
Data/Observations
Complete the Data/Observations section for this experiment either on your Report Sheet or in
your lab report as directed by your teacher.
1. Table 7.1 lists clues that a chemical reaction has occurred. Which of the observations you
made support that a chemical reaction has occurred in the experiment?
2. What mass of copper was formed?
Analysis and Conclusions
Complete the Analysis and Conclusions section for this experiment either on your Report Sheet
or in your lab report as directed by your teacher.
1. Which reactant was limiting? What observations support this? Also, use the chemical equation
for the reaction that occurred in this lab and stoichiometric calculations to support your answer.
2. Why were the amounts chosen so this reactant (see number 1 above) was limiting? What
would be a problem with having the other reactant as the limiting reactant?
3. Why was the copper washed with water (step 9 of the procedure)?
4. Why didn't the water added to the copper (II) sulfate have to be measured exactly?
5. What is the formula for the iron-containing compound that is formed when copper (II) sulfate
and iron react? Support your answer.
Something Extra
Remove the copper metal and let the solution stand for a few days. What happens? Explain.
Stoichiometry
Prelaboratory Questions
1. Write out and balance each of the following equations.
copper(II) sulfate(aq) + iron(s) → copper(s) + iron(II) sulfate(aq)
copper(II) sulfate(aq) + iron(s) → copper(s) + iron(III) sulfate(aq)
2. If iron(III) sulfate were formed, what mass of copper would be expected?
3. If iron(II) sulfate were formed, what mass of copper would be expected?
Data/Observations
1. Table 7.1 lists clues that a chemical reaction has occurred. Which of the observations you
made support that a chemical reaction has occurred in the experiment?
2. What mass of copper was formed?
Analysis and Conclusions
1. Which reactant was limiting? What observations support this? Also, use the chemical equation
for the reaction that occurred in this lab and stoichiometric calculations to support your answer.
2. Why were the amounts chosen so this reactant (see number 1 above) was limiting? What
would be a problem with having the other reactant as the limiting reactant?
3. Why was the copper washed with water (step 9 of the procedure)?
4. Why didn't the water added to the copper(II) sulfate have to be measured exactly?
5. What is the formula for the iron-containing compound that is formed when copper(II) sulfate
and iron react? Support your answer.
Something Extra
Remove the copper metal and let the solution stand for a few days. What happens? Explain.
Experiment 37
Stoichiometry
Introduction
Intent
Students will determine the stoichiometry of a reaction between iron filings and copper(II)
sulfate. The students will determine the equation for the reaction by making appropriate
measurements and calculations.
Objectives
1. To determine the mass of copper formed in a reaction.
2. To use this information to decide the identity of one of the products.
Materials (for each lab team of 2 students)
Apparatus
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Safety goggles (2)
Lab apron (2)
2 250-mL beakers
Ring stand
Ring
Wire Gauze
Bunsen burner
Balance
Stirring rod
Matches
Drying Oven
Acetone
Reagents
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Copper (II) sulfate (anhydrous) (7.00 g)
Iron filings (2.00 g)
Water
Preparation Hints
Place containers of copper(II) sulfate and iron fillings throughout the lab for easier access.
Prelaboratory Discussion
Students should tie back their hair and loose clothing whenever they work with a flame in the
lab. Students will often deposit matches in the sink. Let them know to dispose of burned matches
in the trash can after they are cooled.
Remind students of the locations of eyewashes. If students come in contact with any solution
they should wash the contacted area thoroughly.
You may wish to demonstrate to the students how to pour a solution down a stirring rod.
Procedure Hints
Wash the copper with acetone and use a drying oven for a short period of time to remove the
acetone.
Disposal
1. Collect the decanted solution from the students and dispose according to local regulations for
solutions containing copper and iron ions.
2. Collect the copper from the students. This could be used in other experiments or discarded as
copper metal.
Postlab Discussion
Review how to determine the limiting reactant. In this case since the students do not know the
chemical reaction, they must determine this by observation. If copper is in excess what color will
the solution be at the end of the reaction?
Some students may require assistance in connecting the masses used to the balanced equation
and to the formula for the product.
Stoichiometry
Prelaboratory Questions
1. Write and balance each of the following equations.
copper(II) sulfate (aq) + iron (s) → copper (s) + iron (II) sulfate (aq)
CuSO4(aq) + Fe(s) → Cu(s) + FeSO4(aq)
copper(II) sulfate (aq) + iron (s) → copper (s) + iron (III) sulfate (aq)
3CuSO4(aq) + 2Fe(s) → 3Cu(s) + Fe2(SO4)3(aq)
2. If iron(III) sulfate were formed, what mass of copper would be expected?
In this case, CuSO4 is limiting and 2.79 g of Cu can be formed.
3. If iron(II) sulfate were formed, what mass of copper would be expected?
In this case, Fe is limiting and 2.27 g of Cu can be formed.
Data/Observations
1. Table 7.1 lists clues that a chemical reaction has occurred. Which of the observations you
made support that a chemical reaction has occurred in the experiment?
Answers will vary. Sample answers should include: the color of the solution changed slightly (to
a lighter blue) and a new material was formed.
2. What mass of copper was formed?
Answers will vary (should be around 2.28 g).
Analysis and Conclusions
1. Which reactant was limiting? What observations support this? Also, use the chemical equation
for the reaction that occurred in this lab and stoichiometric calculations to support your answer.
The iron was limiting. This can be seen because the solution remained light blue after the
reaction was complete. The calculations from the prelaboratory questions can be used to support
this.
2. Why were the amounts chosen so this reactant (see number 1 above) was limiting? What
would be a problem with having the other reactant as the limiting reactant?
If the copper(II) sulfate was limiting, iron would be left over. It would be difficult to separate the
iron and copper metal in order to get a mass of the copper.
3. Why was the copper washed with water (step 9 of the procedure)?
The water is used to wash the copper(II) sulfate or iron(II) sulfate from the copper.
4. Why didn't the water added to the copper(II) sulfate have to be measured exactly?
The water provided the medium for the reaction. It did not take part in the reaction.
5. What is the formula for the iron-containing compound that is formed when copper (II) sulfate
and iron react? Support your answer.
The formula is FeSO4. This is evidence by the mass of copper produced and the identity of the
limiting reactant.
Something Extra
Remove the copper metal and let the solution stand for a few days. What happens? Explain.
The solution will turn light yellow because the iron(II) sulfate solution will be oxidized by oxygen
in the air to form iron(III) sulfate.