Introduction: (Initial Observation)
Before invention of electric generators, battery was invented. Battery is a device that converts chemical energy to electrical energy (Electricity).
For many years scientists used electricity from batteries and made electromagnet and devices that are based on electromagnet such as telegraph, microphone, speaker, buzzer, telephone and electromotor.
Batteries have been made with many different chemical compounds. In general batteries use the chemical reaction between three or more substances to create a flow of electrons. 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.
I got the idea for this project when I heard about Air-Aluminum fuel cell. I wanted to know if air really is a factor in production of electricity.
In this project you will make a salt water battery and then perform a series of experiments to determine how does the amount of oxygen affect the life and the power of the battery.
Information Gathering:
What is electricity and how is it made?
Electricity is moving electrons in a conductor such as a copper wire. But what can force these electrons to move?
There are two different ways that electricity can be made.
First method is using a chemical reaction. For example batteries make electricity by a chemical reaction.
Second method is by using magnet. Moving magnets next to a wire, can force electrons move inside the wire.
For making electricity using magnet, check the following links for information:
Making electricity using magnet is not a simple experiment, specially if you want to produce enough electricity to light up a bulb. So most likely you are nor going to make an electric generator for your project; but drawings in the above sites may be reproduced in a larger size and be used in your display.
For making electricity using a chemical reaction, visit this link:
Question/ Purpose:
What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.
The purpose of this project is to construct a saltwater battery and determine how does the amount of oxygen affect the time the battery will last.
Identify Variables:
When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.
Independent variable also known as manipulated variable is the amount of oxygen or the amount of air available to the electrodes.
Dependent variable also known as responding variable is the the time the battery will last.
Controlled variable is the temperature. (perform all experiments at the same temperature; room temperature)
Constants are:
- The amount and the concentration of salt water, the type and the size of electrodes.
- Type and size of electrodes (We use Iron and Magnesium electrodes for all experiments)
- Contact area of electrodes with electrolyte
Hypothesis:
Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.
My hypothesis is that the battery will last longer if more oxygen is available to the electrodes. (Maybe that is why they call it air battery).
Note: You can come up with your own hypothesis.
Experiment Design:
Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”
Experiment 1: Make an air-salt battery
Introduction: In this experiment you will make an air-salt battery and make it work so you can light up a small light bulb.
Procedure:
- In a 400 ml Beaker or a glass or ceramic cup add 2 spoonful table salt. (You may also use a plastic container instead of a beaker or a cup. The ratio of salt to water is 1 to 4, so you may mix one cup of salt with 4 cups of water.)
- Add warm water to the cup to about 2 centimeter from the top.
- Use a plastic spoon to stir the salt water for about 3 minutes. Some salt may remain at the bottom of the cup.
- Let the salt water cool off to the room temperature for about 1 hour.
- Insert a wooden or plastic divider in the middle of the cup. A divider will ensure that two electrodes will not touch each other. Without a divider, you just need to be more careful and keep the electrodes on two opposite sides of the cup.
- Screw the miniature light bulb in the miniature base.
- Connect two pieces of wires to the base. To do that you must loosen the connection screws of the base; remove the insulation from the ends of the wires, make a small loop on one end of each wire and place them under the screw; and then tighten the screw.
- Connect the other ends of the wires to the alligator clips. To do that you must loosen the screws on the alligator clips; pass each wire through the hole in one alligator clip; form a small loop of wire under the screw and then tighten the screw.
- Connect one alligator clip to the Magnesium electrode. You may connect it to more than one electrode in order to get more electric current.
- Connect the other alligator clip to the iron electrode (or steel wool).
- Insert both electrodes in two opposite sides of the salt water cup so they will not be touching each other. See the light bulb. Do you see the light? (At this time if you have used steel wool as your iron electrode, you must see the light. If you are using a flat iron electrode, most likely you will not get light; however, if you add some hydrogen peroxide to the salt water, light must start. shaking the iron electrode will also help to get more light. If you are using steel wool and the light stops, remove it from the solution so it can get some air and then insert it back again to get light.)
Which one is the positive pole?
Identifying the polarity or direction of electricity is especially important when you are trying to light up an LED (Light Emitting Diode).
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.
Experiment 2: How does the amount of oxygen affect the production of electricity?
Introduction: With an air battery or salt water battery, you can perform experiments to determine how does the concentration of salt water or the availability of oxygen affect the production of electricity (minutes or seconds the light stays on). Such experiments are especially recommended because you can use them to collect data, have a results table and make a graph. In this experiment we will test the effect of added oxygen in the form of hydrogen peroxide.
Procedure:
- Construct your saltwater battery using a steel wool and a magnesium electrode as you did in the previous experiment. (Do not add salt water yet. Use clamps or tape to hold the electrodes in place so they will not move around during your experiment). Since magnesium electrodes are usually small, you may need to connect 2 or 3 magnesium electrodes to each other (side by side) to give a larger surface contact to your magnesium electrodes.
- Prepare about one gallon saturated salt water in another container. This must be enough for a few experiments.
- Use a measuring cylinder or any other measuring cup to add saltwater to your battery container. Make sure at least 3/4th of the electrodes are in salt water. Record the amount of salt water you added.
- Observe and record the number of seconds the light stays on.
- Empty the salt water.
- Repeat the steps 3 to 5 with salt water solutions that have 5 ml, 10 ml and 15 ml added hydrogen peroxide.
- Your data table may look like this:
| Total salt water | Total peroxide added | percent of Hydrogen peroxide | Seconds of light |
| 500 ml | 0 | 0 | |
| 500 ml | 5 ml | 1 | |
| 500 ml | 10 ml | 2 | |
| 500 ml | 15 ml | 3 |
Ratio of added hydrogen peroxide is what you calculate by dividing the total peroxide added by the total saltwater.
Make a graph:
You may use the above table to make a graph (bar graph or line graph). To make a bar graph, you will make one vertical bar for each of the hydrogen peroxide concentrations you have tested. Write the concentration or the percentage below each bar. The height of each bar will represent the number of seconds the light stayed on.
If you connect the top of the bars with a line, that will be a line graph.
Experiment 3: How does the amount of oxygen affect the produced voltage?
Introduction: With an air battery or salt water battery, you can perform experiments to determine how does the concentration of salt water or the availability of oxygen affect the production of electricity (voltage). Such experiments are especially recommended because you can use them to collect data, have a results table and make a graph. In this experiment we will test the effect of added oxygen in the form of hydrogen peroxide.
Procedure:
- Construct your saltwater battery using a steel wool and a magnesium electrode as you did in the previous experiment. (Do not add salt water yet. Use clamps or tape to hold the electrodes in place so they will not move around during your experiment). Since magnesium electrodes are usually small, you may need to connect 2 or 3 magnesium electrodes to each other (side by side) to give a larger surface contact to your magnesium electrodes.
- Set your voltmeter to 2.5 Volts DC or any other DC volt range higher than 1.
- Connect the probes of the voltmeter to the electrodes. The red wire goes to the iron and the black wire goes to the magnesium electrode. (If you try the opposite order, the needle moves backward. In other words the iron is the positive pole and the magnesium is the negative pole)
- Prepare enough saturated salt water in another container.
- Have a pipette or medicine dropper ready for adding known amounts of hydrogen peroxide.
- Use a measuring cylinder or any other measuring cup to add saltwater to your battery container. Make sure at least 3/4th of the electrodes are in salt water. Record the amount of salt water you added.
- Observe and record the voltage shown by your voltmeter. Make another observation and recording of the voltage after 1 minute. Take the average of your two observations and report that as the voltage with no added oxygen.
- Add 2 ml (or 5ml or any other known amount) hydrogen peroxide. Observe and record the voltage 2 times, 1 minute apart and take the average again.
- Continue adding hydrogen peroxide and repeat your observations and recording. Your data table may look like this:
| Total salt water | Total peroxide added | Ratio of Hydrogen peroxide | Average Voltage |
| 500 ml | 0 | 0% | |
| 500 ml | 5 ml | 1% | |
| 500 ml | 10 ml | 2% | |
| 500 ml | 15 ml | 3% |
Ratio of added hydrogen peroxide is what you calculate by dividing the total peroxide added by the total saltwater.
Make a graph:
You may use the above table to make a graph (bar graph or line graph). To make a bar graph, you will make one vertical bar for each of the hydrogen peroxide concentrations you have tested. Write the concentration or the percentage of hydrogen peroxide below each bar. The height of each bar will represent the average voltage you calculated for each concentration of hydrogen peroxide.
If you connect the top of the bars with a line, that will be a line graph.
Materials and Equipment:
- 2 to 4 Magnesium Electrodes
- 1 Steel Wool as Iron Electrode
- 2 Alligator clip lead wires
- 1 Lb table salt or cooking salt
10 Oz Hydrogen Peroxide - 1 small Light bulb with base. (1.2 Volts bulb is the best and you will have more chance to see some light)
- 1 low voltage LED (It is easier to get light from LED)
Additional Optional Materials:
- Galvanometer or voltmeter capable of showing millivolts. (Can be purchased from electronic stores or online from MiniScience.com)
Note: Magnesium electrode does not have much use, that is why it is not sold in regular stores. Only scientific suppliers may sell magnesium electrodes. Some of the online stores that sell electrodes are: MiniScience.com, klk.com and ScienceProjectStore.com.
Results of Experiment (Observation):
Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.
Calculations:
If you do any calculations for this project, write your calculations in this section of your report.
Summary of Results:
Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.
It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.
Conclusion:
Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.
Related Questions & Answers:
What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.
Possible Errors:
If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.
If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.
Does degreasing and cleaning electrodes from oil and grease affect the amount of voltage?
References:
List of References
http://www.electric-fuel.com/evtech/papers/duisburg.pdf
http://www.zyn.com/flcfw/fwtproj/ZincAirB.htm
http://chemlearn.chem.indiana.edu/demos/Zinc.htm
http://quiz2.chem.arizona.edu/preproom/Demo%20Files/cu-zn_battery.htm
To find more references, search the Internet for Voltaic Cell or Galvanic Cell. What you are making in this project is really a voltaic cell; however, you are using fruit juice instead of chemicals as Electrolyte.
Question: I could not get a light with a 1.2 volt light bulb. What may be wrong?
Answer: 1.2 volt light bulb requires a lot of current. To increase the current you must increase the surface contact of electrodes with salt water. To do this make sure that at least 90% of the electrode is inserted in the saltwater. Also use multiple electrodes. As a final solution, add a little hydrogen peroxide to the salt water to expedite oxidation of iron.
The diagram in the right shows 3 magnesium electrodes hanged in one side and one large pack of steel wool is on the opposite side. If you are using iron electrodes instead of steel wool, you must use multiple electrodes.
Usually 2 magnesium electrodes and one steel wool sponge are enough to get light.
Also make sure that the saltwater is very strong (lots of salt).
Question: I got light from the light bulb, but not from LED. Why didn’t the LED light up?
Answer: It is much easier to light up an LED and you even don’t need to add hydrogen peroxide. LEDs don’t need much current, so a single electrode must work as well. The only problem is that LEDs need a higher voltage. You must make two saltwater battery and connect them in series in order to double the voltage.
As you see in this diagram, we are using two cups of saltwater. Each cup has one iron electrode and one magnesium electrode. In order to connect two cups you must connect the magnesium electrode of one cup to the iron electrode of another cup using a connection wire. The remaining electrodes will be connected to the LED. Since each saltwater battery generates about 1.5 volts, the two batteries together provide about 3 volts that is enough for most low voltage LEDs.
