Expt 014 -- Aluminum Corrosion

Copper(II) causes aluminum metal to react under certain circumstances. Conditions under which the aluminum reacts are determined.

Introduction

• Aluminum is a very reactive metal never found in nature as the unreacted element. Unlike other reactive metals, however, aluminum forms a coating of oxide that protects it from further reaction with the oxygen of air.
• A well-known macro demonstration involves taking an aluminum soda can, using a nail to scratch the inside of the can (to break a plastic coating), and then treating the can with aqueous CuCl₂. After a relatively short time, the can weakens so much that it can easily be pulled apart into two pieces.

Safety

Sharp edges from aluminum cans can cause cuts. Handle the pieces of aluminum with great care to avoid cuts. Some of the materials used are toxic. Wear goggles and apron. Do not ingest the chemicals. Wash hands after the experiment.

Procedure

This experiment has three different forms that may be used. An aluminum soda can may be cut up and scratched for the experiment. Or, household aluminum foil may be used in place of pieces of can. You may either immerse the foil in wells of chemicals, or add drops of chemicals directly onto the foil. Do not scratch the foil. Use the method suggested by your instructor.

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Use a magnifying glass for careful observation of the corrosion in all methods.

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Aluminum Can:

1. Obtain 7 pieces of aluminum can, each about 3 cm x 3 cm. Use a nail to scratch the shiny surface of the piece.

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2. Place the following chemicals on the pieces of can, and observe.

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   • Piece 1: 20 drops 0.2 M CuCl₂
   • Piece 2: 20 drops 0.2 M CuSO₄
   • Piece 3: 15 drops 0.2 M CuSO₄ + 5 drops 0.1 M NaCl
   • Piece 4: 15 drops 0.2 M CuSO₄ + 5 drops 0.1 M H₂SO₄
   • Piece 5: 15 drops 0.2 M CuSO₄ + 5 drops 0.1 M HCl
   • Piece 6: 20 drops 0.1 M H₂SO₄
   • Piece 7: 20 drops 0.1 M HCl
3. Note the reactions.

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Foil in 24-well plate:

1. Add the reagents above to 7 wells of a 24-well plate. Crumple 7 small pieces of Al foil, and immerse one in each solution in the 24-well plate.
2. Note the reactions.

   !!!Click here to See Picture.

Drops on foil:

1. Drop the reagents above directly on the aluminum foil in 7 separate puddles. Where one reagent is add, use 4 drops. Where 2 reagents are added, use 3 drops of CuSO₄ and 1 drop of the other reagent.
2. Note the reactions.

   !!!Click here to See Picture.

Questions

1. On the basis of the observations, write a chemical equation for the corrosion of the aluminum.
2. Describe a role, if any, played by the Cl^-.

Handout

Name ___________________________ Class ________

Teacher__________________________

SmallScale 014 Aluminum Corrosion

Makeup students should watch the movies and record observations for the first 5 reagents.

Reactants Observations

1. CuCl₂
2. CuSO₄
3. CuSO₄ + NaCl
4. CuSO₄ + H₂SO₄
5. CuSO₄ + HCl
6. H₂SO₄
7. HCl

Curriculum-

Use this activity when discussing oxidation, reduction, redox, corrosion, applied chemistry, metals, or chemical reactions.

Safety-

• Sharp edges from aluminum cans can cause cuts. Handle the pieces of aluminum with great care to avoid cuts. Some of the materials used are toxic. Wear goggles and apron. Do not ingest the chemicals. Wash hands after the experiment.
• The teacher should be extremely careful when cutting cans. Wear heavy gloves when cutting cans to avoid cuts.

Time-

Teacher Preparation: 30 minutes

Class Time: 30 minutes

Materials-

• 1 mL of 0.2 M CuCl₂ (Add 3.41 g CuCl₂•2H₂O to enough water to make 100 mL of solution.)
• 4 mL of 0.2 M CuSO₄ (Add 4.99 g CuSO₄•5H₂O to enough water to make 100 mL of solution.)
• 1 mL of 0.1 M NaCl (Add 0.584 NaCl to enough water to make 100 mL of solution.)
• 2 mL of 0.1 M H₂SO₄ (add 3.3 mL 3 M H₂SO₄ to enough water to make 100 mL of solution.)
• 2 mL of 0.1 M HCl (add 3.3 mL 3 M HCl to enough water to make 100 mL of solution.)
• nail
• (gloves, snips, aluminum cans or aluminum foil)
• (1 24-well plate per group for one version)

Disposal-

The liquids used in this experiment may be discarded safely with running water at the sink. The solids may be discarded with ordinary solid trash.

Background-

When treated with dilute aqueous HgCl₂, metallic aluminum (as in a fairly heavy pie tin) experiences rapid air oxidation. The metals can be seen to crumble and flake in the air as if diseased. Mercury compounds are not permitted in many classrooms. See this dramatic oxidation and show it to the students from the Redox Videodisc available from Synaps.

Data Table-

1. CuCl₂ Darkbrown Cu crystals form
2. CuSO₄ No reaction
3. CuSO₄ + NaCl Fewer Darkbrown Cu crystals
4. CuSO₄ + H₂SO₄ Slight reaction (light brown)
5. CuSO₄ + HCl Fewer Cu crystals + bubbles
6. H₂SO₄ No reaction
7. HCl Bubbles No crystals

The movies do not display reactions 6 and 7.

Answers-

Q1. On the basis of the observations, write a chemical equation for the corrosion of the aluminum.

A1. 3 CuCl₂ + 2 Al --> 2 AlCl₃ + 3 Cu

Q2. Describe a role, if any, played by the Cl^-.

A2. The chloride seems to be acting as a catalyst for the reaction.

Key Words 1-

oxidation, reduction, redox, corrosion, applied chemistry, metals

Elements-

Al Cu Cl S