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Air Battery

Make a battery that works with air and saltwater

Introduction: 

Batteries have been made with many different chemical compounds. Scientists often try to make batteries that provide more energy and last longer. Many of such high quality batteries are commercially available today. They are used in flashlights and electronic devices such as radios, watches, computers and calculators. Making a battery is always an exciting science project. Your home made batteries can be used as chemistry, physics or electricity project.  Click here to see the instructions for Advanced Kit.

A battery is made of two different electrodes inserted in a chemical compound. A chemical reaction between the electrodes and the chemical compound produces electricity. For example if you insert a copper rod and an iron rod in a cup of orange juice, that will be a battery. In this example copper rod and iron rod are the electrodes and the orange juice is the chemical compound or electrolyte. The problem is that the electricity produced by such a battery is too little and has no practical use and you cannot use it to light up a light bulb. The saltwater battery described in this project guide can light up a light bulb for a few seconds. When the light goes off, you can simply empty the used salt water and add fresh salt water to get light again. By adding a small amount of hydrogen peroxide you can get more light and the light will last longer.

List of materials you need:

This is the minimum list of material you need for your experiment. Miniature light bulb (low voltage, low current) Miniature base for light bulb Pair of red insulated copper wire with alligator clips Pair of black insulated copper wire with alligator clips Magnesium Electrode s Iron Electrodes A cup of saltwater (not in the picture) Screws for the miniature base. Hydrogen Peroxide (Optional)

Additional optional materials you may use:

1. A wooden board to mount the miniature base (light holder)
2. Plastic container about 4" x 4" x 4"
3. Hydrogen Peroxide

What is a good title for my project? You can call it "Air battery", "Salt water battery", "electricity from air" or "electricity from the salt water".

Procedure:

1. Loosen the screw on both contacts of the bulb holder. Clip one end of the red wire to one screw, and clip one end of the black wire to the other screw. 
2. Screw the light bulb on the miniature base.
3. Connect the remaining red alligator clip to the iron electrode  (Steel wool) and secure it on one side of the plastic container or the cup.
4. Connect the remaining black alligator clip to the magnesium electrode (2 of them) and secure it on the opposite side of the container. (You may need to hold them by hand or use a small tape to hold them in place on the side of the container.
5. In another pitcher, prepare some strong, warm salt water. Add enough salt so at the end some salt will remain at the bottom of the pitcher.
6. Transfer the salt water from the pitcher to the container. 
7. At this time, if all the connections are secure and the electrodes are large enough, you should get a light.

In this diagram two magnesium electrodes are used at the same time in order to get a higher electric current.  In this process magnesium will be consumed and converted to magnesium hydroxide. Half of the steel wool is enough for this experiment.

How can I get more light?

Make sure your electrodes are not touching each other. Make sure there is nothing blocking the space between the electrodes. Make sure that the alligator clips are not touching the salt water. Both electrodes must have the maximum possible surface contact with salt water.

The test tube electrodes (magnesium electrodes in test tubes) are formed like a spring. This provides the largest possible surface contact. For Iron electrode you may use steel wool. Steel wool has a very large surface contact. A steel screen may work as well.

You may notice that you will get more light if you stir the solution or if you remove the iron electrode and insert it back again. Such actions provide oxygen to the surface of the iron.

Note: Steel is about 98% iron.

The oxygen in the air may not be enough for your demonstration and you may get a dim light.  In this case you may add some oxygen (in the form of hydrogen peroxide) to the salt water. That should immediately increase the light.

A cup is relatively small. If you have access to a larger container, you will get a better result. In a larger container, it is easier to secure the electrodes in two opposite sides so they will not touch each other.

Where to buy the material? The main components of this project are available as a set in MiniScience.com online store and KidsLoveKits.com. This set will only include the essential components. You must have a plastic container, a wooden board, some iron and some hydrogen peroxide to complete your material. This set includes 2 Magnesium electrodes, insulated wire, light bulb, light base, alligator clips and screws. Part# AIRBAT

The electricity produced in this way may be used to light up a light bulb, an LED or run a low voltage electric motor. Identifying the polarity or direction of electricity is especially important when you are trying to light up an LED.  Each LED has 2 legs. One is longer than the other. The longer leg must be connected to the positive pole of the battery or Iron. The shorter leg must be connected to the negative  electrode or Magnesium.

Light up the LED: In addition to a low voltage light bulb, your kit also includes a super bright LED that can light up with your saltwater battery. Since LEDs do not need a large electrical current, you will not have to use two magnesium electrodes side by side. On the other hand LEDs require more voltage; so you must make at least two saltwater battery and connect them in series in order to produce higher voltage.
When using LEDs, the longer leg must be connected to the positive pole (Iron) of the battery. The shorter leg must be connected to the negative  electrode (Magnesium).  The following diagram shows how these two saltwater batteries must be connected.
	If you don't have the materials for this experiment, you can order it now.

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Does it really work?

Although a saltwater battery is not as strong as a real battery, it can produce visible light on a low voltage light bulb. It is also safer than batteries that use many harmful chemicals.

The only chemical that you need is Sodium Chloride (NaCl) also known as table salt. This is the chemical that you usually have it at home. If not, you can buy it from grocery stores. Good quality, pure and inexpensive packages of salt are often marked as kosher salt. You also need water (H2O).

Some articles suggest using Aluminum and Copper metals as electrodes; however, I have not been able to verify that. I suggest using iron and magnesium metals. Of course you can test any combinations of metals that you like. Inexpensive metal electrodes are available at MiniScience.com or KidsLoveKits.com.

Suggested List of material:

1. Salt and water

2. Iron electrode. For best results use steel wool or steel screens as electrode. High surface area of steel wool or steel screen will simplify the production of electricity.

3. Magnesium electrode

4. Wire lids with alligator clips

5. Miniature light bulb (Low voltage)

6. Miniature base

7. Wooden board to mount the Miniature Base

8. Screws for Miniature base

When Iron and magnesium are placed in water, multiple chemical reactions happen that contribute to the movements of electrons from magnesium electrode towards iron electrode. During these processes Iron electrode oxidizes to Iron oxide and magnesium electrode reduces to magnesium hydroxide.

Here's what is happening in more details:

• Magnesium have a tendency to react with water and form magnesium hydroxide. To do this each magnesium atom must lose one electron (and become Mg+ ions). While the magnesium electrode is loosing electrons it will form the negative pole.
• The electrons from the magnesium atoms combine with the hydrogen ions in the water and form H2 molecules (Hydrogen gas). We see the hydrogen gas as bubbles forming on the magnesium.
• On the other electrode, the iron that is oxidized by air and is now in the form of Fe++ ion needs to receive two electrons to change back to iron. This will create shortage of electrons in the iron side and make the iron a positive pole.