Advanced-Level Science Projects: Chemistry

Chemistry

Which Metal Corrodes the Fastest?

Did you ever have a shiny new bike that over time got to look not so shiny and new anymore? Or some beach chairs that got left outside over the winter and by spring looked like they were ready for the trash heap?

If so, chances are that the culprit was rust. Mailboxes, swing sets, lamps, cars, railings, and just about anything else made from metal are subject to the perils of rusting—a deteriorating metal condition.

You've undoubtedly had some experience with rust—or at least have seen it on a car or other object. Rust is so common that its color also is called rust, as in rust-colored leaves, or rusty-brown hair.

In this section, you'll learn a lot more about rust and how it occurs. And you'll attempt to find out which metals rust the fastest, by exposing them to water and to salt water.

So What Seems to Be the Problem?

Rust occurs when metals containing iron react with the oxygen in the air or in water and form a compound called iron(III) oxide (ferric oxide). This compound contains water molecules, so we call it a hydrated compound.

Both oxygen gas and water must be present for the iron to rust. Chemically and very simply speaking, iron atoms lose a few electrons to oxygen atoms. This process by which electrons are removed from atoms is called oxidation. When oxidation occurs, it produces a chemical reaction that creates iron(III) oxide—or rust.

Rust is a type of corrosion. But it's not the only type. Other forms of corrosion include:

• Tarnish found on silver teapots, trays, and jewelry
• Copper carbonate, or patina, the corrosion that causes copper to turn green
• Discolored spots that appear on brass
• Aluminum oxide, which forms on aluminum
• Chromium oxide, which forms on the outside layer of stainless steel

On some metals, corrosion actually serves as a type of protection. Aluminum oxide, copper carbonate and chromium oxide, for instance, act as protective coatings for the underlying metals.

Rust that forms on iron, however, cannot protect the iron from further corrosion because it's too porous.

The problem you'll be attempting to solve in this science fair project is which metals corrode the fastest, and under which conditions. You'll test five metals—silver, steel, zinc, copper, and aluminum—to see which corrodes fastest in water and in salt water.

When you've finished, you'll have a better understanding of corrosion, the process of oxidation, and the properties of different metals.

The title of this section, “Which Metal Corrodes the Fastest?” would be a suitable title for your science fair project. Other possible titles include:

• Which Metal Holds Up Best in a Corrosive Environment?
• Understanding How Corrosion Affects Common Metals

Or, you can think of a name for your project on your own. Let's take a few minutes now to consider why this project is valuable.

What's the Point?

Why should you care which of the five metals you'll be testing corrodes the quickest? Why should you care about metals at all, for that matter?

Metals have thousands of uses that affect our everyday lives, most of which we take for granted. Copper, for instance, is pliable and a good conductor of electricity. For those reasons, it's used to make the wire inside of electrical cables. Without electrical cables we'd have no electricity in our homes—no light, TV, or video games.

Aluminum is extremely strong and can be fashioned into thin sheets, making it vital for aircraft production. Think about that the next time you climb onto an airplane. Metals are used to make the utensils we eat with, the coins we use to buy what we want, and the cars we drive.

Obviously, metals that are used to build aircraft, cars, and electrical wiring had to be extensively tested to make sure they were suitable for use.

You can be sure that there was far-reaching research and experimentation before the first copper wire was put to use in an electrical cable. Metallurgists—experts on metals—are constantly looking for new uses of metals in many fields, including medical, military, and aeronautics.

Metals—and how they're used—are extremely important. Once you know how different metals hold up to corrosion, you'll be able to better understand why they have particular roles, and why they're important. In addition, you'll be able to give Mom and Dad some pointers the next time they're shopping for a new outdoor lamp or metal toy for your little brother.

By experimenting with five different types of metal wire, you'll be able to see which corrodes the fastest, and which ones hold up best under certain circumstances. You'll test each wire in both distilled water and salt water. Again, the types of metal you'll be testing are:

• Silver
• Steel
• Zinc
• Copper
• Aluminum

Your control group will be 10 pieces of wire—two each of the metals listed above. The variables are the distilled water and the salt water in which the metal wires will be immersed. Using the scientific method, you'll learn which metal begins to corrode first, and which holds up the best.

What Do You Think Will Happen?

Think about what you may already know about different kinds of metals and how they react when exposed to rain, or air or water that contains a lot of salt. This will help you to formulate a hypothesis based within the context of knowledge you already possess.

Go back to the bicycle mentioned in the first sentence of this section. Under what type of circumstances did your bike rust? When it was stored in the dry garage? Or when you left it lying out in the yard for three days during a steady rain?

Why do you suppose that cold-weather drivers are advised to rinse off their cars every now and then during the winter season when road salts are being used? Have you ever noticed or heard people talk about problems with corrosion near the beach, where salt water is prevalent?

Do you already know, perhaps, which metals are most resistant to corrosion? If so, the experiment you'll do will support and affirm your knowledge. If you don't, try to use common sense and any information you may have about this topic to come up with your best guess—or hypothesis.

Materials You'll Need for This Project

The experiment you'll be doing will require only a short amount of time to set up, but you'll need to make observations over a 10-day period.

It's going to be important to write down exactly what you see happening to each metal each day. Remember that your measurements will be qualitative, not quantitative. For that reason, the more data you present concerning your experiment, the more reliable your results will be.

You'll need some materials for this experiment that probably aren't lying around your house. You should be able to find everything you need, however, at your local hardware or home supply store. You will need:

• 12 inches (30.5 cm) of silver wire
• 12 inches (30.5 cm) of steel wire
• 12 inches (30.5 cm) of zinc wire
• 12 inches (30.5 cm) of copper wire
• 12 inches (30.5 cm) of aluminum wire
• Small pair of wire cutters (or ask the person at the store who cuts the wires for you to cut each 12-inch piece in half)
• 10 clear drinking glasses (preferably identical), or 10 test tubes and a test tube rack
• A pen or fine-point marker
• Small pieces of paper or labels for the glasses or test tubes
• 10 pencils (they don't need to be sharpened)
• Transparent or masking tape
• Liquid measuring cup
• A tablespoon measure
• A funnel
• Distilled water (available in gallon jugs in most grocery stores)
• Table salt

If you can get test tubes and a rack, you'll probably find them easier to use than glasses. If you have to use glasses, however, that's fine. You can use plastic or glass cups; just make sure that they're clear so you're able to easily observe what's happening to the wires in them.

Conducting Your Experiment

Make sure that you have all your materials ready before you begin the experiment. Be sure to find an area large enough to accommodate the glasses or test tubes, where they will be undisturbed for the duration of your experiment.

Follow these steps:

Wires of different materials are suspended in distilled water and salt water.

1. If the five wires aren't already cut, cut them into 6-inch lengths.
2. Using the pen or marker, mark ten labels or small pieces of paper as follows:
   • water + silver
   • salt water + silver
   • water + steel
   • salt water + steel
   • water + zinc
   • salt water + zinc
   • water + copper
   • salt water + copper
   • water + aluminum
   • salt water + aluminum
3. Set the glasses or test tubes on a table or counter where you'll be able to easily observe them.
4. Stick a marked label, or tape a piece of marked paper, on each glass or test tube. Face all labels front so you can easily see them.
5. Using the measuring cup and funnel, fill five glasses or test tubes with distilled water.
6. Mix 8 ounces (240 ml) of water with 1 tablespoon of salt. Stir until the salt is completely dissolved.
7. Fill the other five glasses or test tubes with the salt water solution, mixing more water and salt as needed.
8. Wrap one end of each piece of wire around a pencil, so that when the pencil rests across the top of the glass, the wire hangs to the bottom.
9. Observe each wire at least once a day for 10 days. Use the charts found in the following sections, or make your own charts.

Remember that the more clear and accurate your observations are, the better you'll be able to draw conclusions from your experiment.

Keeping Track of Your Experiment

Use the charts on the following section, or make your own, similar charts to keep track of what you observe during the course of your experiment.

Be sure to not mix up the glasses. They'll all look very similar, so be sure that the labels remain intact and you can see them clearly.

Putting It All Together

Some observations you'll want to consider are how the changes to the metal wires immersed in the distilled water compared to the wires in the salt water. Which metals had the most rust? Was the formation of the rust on any of the wires concentrated on one particular area on the wire? Or was the corrosion distributed evenly along the immersed wire? Based on your data, which metal would you recommend for the manufacture of bikes, beach chairs, and swing sets—not to mention aircraft and medical equipment?

Once you've recorded your results, you can draw a conclusion and identify the answer to the problem you stated at the beginning of your project.

Further Investigation

If you enjoyed this project and would like to take it a step or two further, you could try one of the following ideas:

• Place the metal wires in different liquids and see what happens. You could try vinegar, club soda, coffee, tea, soy sauce, or any other nonhazardous substance.
• Try using different metals, such as brass, titanium, or zinc.
• Test to see whether different conditions lead to different results. If you place some of the glasses in a cold spot, for instance, and others where it is very warm, do you get different results between the two groups?

Use your imagination to come up with other ways to vary the project and delve a bit further into this issue. Just be sure to keep good, accurate notes.