Bust That Rust!

Difficulty of Project

Easy

Cost

$7.00 for poster board and steel wool pads

Approximate time to complete the project

Two weeks

Project Goal

The goal is for all students to learn how rust occurs and how to prevent rusting.

Materials and Equipment

• A box of steel wool pads.  Although the soap-less kind is preferable, the ones with soap will work equally well.
• Salt
• Water
• Vinegar
• At least two or three of the following:  clear fingernail polish, spray-on car wax, furniture polish, polyurethane finish, and vegetable oil.
• Four saucers or small bowls

Introduction

Rust is a problem almost everywhere in the country except the southwest.  It’s the cause of bridges collapsing (such as happened in 1967 when the Silver Bridge in West Virginia collapsed, killing 46 drivers), cars prematurely aging, and fire escapes failing.  Even your bicycle is not immune from this problem as fenders often become rusty, especially as water slicks up in this area.

Since rust is such a problem, it’s natural to demand an explanation. Rust occurs as iron oxidizes.  This oxidation happens when iron (and its alloys such as steel) is exposed to water or air with high water vapor content.  Iron rusts faster when exposed to salt water, which is why salting snowy roads is hard on cars.  Likewise, bridges over salt water (such as the Golden Gate Bridge) need more regular maintenance.  This is one of the reasons that acid rain caused by pollution is so harmful.

In these experiments, students use steel wood pads to explore how rust occurs.  They will have the opportunity to develop their own anti-rust measures, using clear nail polish, spray-on car wax, vegetable oil and other coatings. Background information

Oxidation occurs when an element (in this case, iron) loses an electron.  Both water and oxygen are required for oxidation – which is why cars in the dry southwest have so little rust compared to cars in rainy Florida.  We see even more rusted-out cars in New England where icy roads are regularly salted. This is because oxidation occurs faster when water is slightly acid.

Iron can be rust-proofed with a variety of water-repellant coatings.  In these experiments, students can try various water-repellent substances that encourage water to “bead-up” – therefore minimizing contact with the water.

High school and older middle school students may be interested in learning in learning the chemistry of oxidation.

Chemistry of Oxidation

Oxidation occurs when an element loses an electron.  We say that the oxidation state of the element has increased when it loses that electron.  Oxidation is the first step in the rusting process:

Fe ? Fe2+ + 2 e-

Here, the 2 e- represents two electrons that were liberated from the iron, leaving a charged iron radical.  The charged radical reacts with oxygen in the presence of water as follows:

4 Fe2+ + O2 ? 4 Fe3+ + 2 O2-

Note:  in the above reaction, the oxidation state of iron increases from Fe2+ to Fe3+.  Since both Fe2+ and Fe3+ are inherently unstable, they will try to spit out hydrogen ions as follows:

H2O ? Fe(OH)2 + 2 H+Fe3+ + 3 H2O ? Fe(OH)3 + 3 H+

The resulting Fe(OH)2 and Fe(OH)3 will lose as water (this is called a dehydration reaction), thereby creating  iron oxide (Fe2O3) – which we call rust.

Terms, Concepts and Questions to Start Background Research

• Oxidation
• Iron oxide
• Electron transfer
• Acid
• Rust

Experimental Procedure

Experiment #1

1. Dampen a steel wool pad with approximately 2/3 cup regular water and put it in a first saucer.  
2. Dampen a steel wool pad with approximately 2/3 cup salt water and put it in a second saucer.
3. Make a mildly acidic solution by mixing 1/3 cup vinegar with a 1/3 cup water.  Use all of this solution to dampen a steel wool pad and put it in a third saucer.
4. Leave an undampened steel wool pad in a fourth saucer.  This is your control.
5. Inspect the steel wool pads at 12 hours, 24 hours, 36 hours, 48 hours, 72 hours and 96 hours.   Which pad rusted the fastest?  The second fastest?  The third fastest? Take pictures of the rusted pads and write up your results.

Experiment #2

1. “Pre-treat” steel wool pads by coating them in any of the following:  clear nail polish, spray-on car wax, vegetable oil, polyurethane finish, and furniture polish.   You do not have to use all of these substances, but try to select at least two.  Which do you think will prevent rust the best?
2. Dampen your pre-treated steel wood pads with water (just as you did in experiment #1) and put them on a saucer.  Come back and observe the steel wool pads at 12 hours, 24 hours, 36 hours, 48 hours, 72 hours, and 96 hours. Which pre-treatment worked the best?  Why?

Bibliography

1. Wikipedia "Rust"
2. How Stuff Works "How Does Rust Work?"