Summary

In this lab, students perform a simple redox reaction using an iron nail and copper(II) chloride solution. They will consider both quantitative and qualitative data collected during the reaction in order to attempt to explain what happened. Students will also create particle diagrams and determine mole ratios of various species in the reaction.

Grade Level

High School

Objectives

By the end of this lab, students should be able to

• Explain the process of gaining and losing electrons.
• Define oxidation and reduction.
• Justify that a reaction is an oxidation-reduction reaction in terms of electron transfer.
• Connect the coefficients of a balanced chemical equation to the mole ratio of reacting species.
• Draw particle diagrams of a redox reaction.

Chemistry Topics

This lab supports students’ understanding of

• Chemical Reactions
• Classification of Reactions
• Balancing Equations
• Oxidation-Reduction Reactions
• Electron transfer
• Atoms and Ions
• Solutions
• Net Ionic Equation
• Stoichiometry
• Mole Ratio

Time

Teacher Preparation: 5-10 minutes

Lesson: Two-three 50 minute class periods

Materials (per lab group)

• 100 mL beaker (2)
• 3” Iron Nail (Flinn Reference No. I0032)
• Approximately 90 mL of 0.5 M CuCl₂ Solution (concentration can vary)
• 25ml of 1 M HCl solution
• Scale
• Drying oven (optional)

Safety

• Always wear safety goggles when handling chemicals in the lab.
• Students should wash their hands thoroughly before leaving the lab.
• When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.
• Solid reaction products can be disposed of in the trash and all solutions can be poured down the sink.

Teacher Notes

• The Reaction: The reaction that occurs in an oxidation-reduction reaction between iron and copper(II). The iron is oxidized, transferring electrons to copper(II) ions that are reduced. As this occurs, red copper metal is seen forming and the solution loses its characteristic blue color as the copper(II) ions leave the solution.
  • Net-Ionic Equation: Fe (s) + Cu²⁺(aq) → Fe²⁺(aq) + Cu(s)
  • Oxidation Half-Reaction: Fe(s) → Fe²⁺(aq) + 2e
  • Reduction Half-Reaction: Cu ²⁺(aq) + 2e ^- → Cu(s)
• Data Collection: The lab consistently produced a 1:1 mole ratio of reacting species, evidence for the oxidation of iron metal to form iron(II), as opposed to iron(III). For improved data analysis, collect the class mass data on the board or in a spreadsheet and keep it from year to year. This way, the average reacting mole ratio will be easier for students to observe as 1:1.
• Sometimes, a yellow-ish layer will form on top of the solution. This is likely due to a coating on the nail. This can be reduced by wiping the nails down beforehand. It should not affect results.

• Timing: This lab occurs over several days (50 minute class periods), but note that the first-day setup can be completed rather quickly by students. Additionally, once students have observed the formation of copper metal on the nail (it happens quickly) they can begin to think about what is occurring qualitatively as a homework assignment, reducing the amount of time spent in class. If you teach on a block schedule, the days will have to be modified slightly.
• Do not try to dry the solid copper in one class period, leave it to dry in the oven at a low temperature for some time to ensure it is dry. You could leave them to dry in open air if necessary. If you use a drying oven, watch the samples carefully and keep at a low temperature or the copper will oxidize. You will know if this happens if the solid turns green.
• Students may think that the red solid produced is rust. Be prepared for this. One way is to have them observe the formation of copper at another time earlier in the curriculum. A common beginning of the year lab is qualitatively observing the reaction of aluminum with copper(II) chloride.
• You could alternatively lead them through the logic that since rust is Fe₂O₃ (they probably do not know this) and rusting is a very slow process involving iron reacting with atmospheric oxygen, that it does not make since that dipping the iron in solution (not in contact with air) could cause the reaction to happen.
• The biggest way to differentiate the post-lab is to vary the amount of information you give to your students and how much you direct the discussion.
• For a pre-lab, you could have students determine what data to collect, how to organize the data, and even come up with a procedure with teacher guidance as to the objectives of the lab.
• Once students identify that electron transfer is occurring, challenge them to represent this in an equation. They will likely produce something akin to: Fe(s) – 2 electrons → Fe²⁺. This opens the door for a discussion about how we don’t use subtraction signs in reactions and how to represent electrons in a half-reaction equation.
• The beakers are notoriously hard to clean after this lab. I recommend using old beakers and committing them to use for this lab each year. To try and avoid this, the teacher can wash the beakers to the best of your ability and then soak them in concentrated nitric acid in a fume hood overnight to try to oxidize the remaining copper. Use caution when handling concentrated nitric acid: wear gloves, apron, and goggles at all times and dispense only in a fume hood. The reaction with copper produces toxic nitrogen dioxide gas.
• Analysis questions are optional. Calculations should be given to students after a class discussion about the reaction.
• For a complete look in to how this lab fits in to the curriculum of the author, please refer to the accompanying article, published in the March 2018 issue of Chemistry Solutions.