Introduction: (Initial Observation)
Fire is one of the first human discoveries, however for many years people did not know how to create fire. Imagine making fire without any matches, papers, or fuels! It is certainly not an easy task. Soon people learned how to control fire and how to use it for heating and cooking. Heat of fire is now used to melt glass and metals, a process that is needed in order to make glass and metal objects.
Although contained fire is very helpful for humans, an out of control fire such as a forest fire, is a disaster.
Every year forest fires around the world destroys millions of acres of wood lands and kill many people and animals. House fires are another sad event that happen daily and leads to the loss of life and property.
Many studies have been done in order to identify the causes of fire and the ways they can be prevented. In general fire needs three elements in order to endure. These elements are fuel, oxygen, and heat. These are known as the fire triangle.
It is good to know what is the role of each element in sustaining fire and which elements have a stronger affect on the process of burning. Elements such as heat, oxygen, and fuel can be studied separately.
In this project you will study the effect of oxygen on the rate of burning.
Adult supervision is required.
Perform experiments away from flammable material.
Information Gathering:
Find out about Fire. Read books, magazines or ask professionals who might know in order to learn about the factors effecting the rate of burning. Find out what is the role of Oxygen in burning. Keep track of where you got your information from.
Following are samples of information that you may find.
Three things must be present at the same time in order to produce fire:
- Enough oxygen to sustain combustion,
- Enough heat to raise the material to its ignition temperature,
- Some sort of fuel or combustible material
These elements start a chemical exothermic reaction that is called fire.
Oxygen, heat, and fuel are frequently referred to as the “fire triangle.” Add in the fourth element, the chemical reaction, and you actually have a fire “tetrahedron.” The important thing to remember is: take any of these four things away, and you will not have a fire or the fire will be extinguished.
Essentially, fire extinguishers put out fire by taking away one or more elements of the fire triangle/tetrahedron.
Fire safety, at its most basic, is based upon the principle of keeping fuel sources and ignition sources separate.
Not all fires are the same, and they are classified according to the type of fuel that is burning. If you use the wrong type of fire extinguisher on the wrong class of fire, you can, in fact, make matters worse. It is therefore very important to understand the four different fire classifications.
Class A – Wood, paper, cloth, trash, plastics
Solid combustible materials that are not metals. (Class A fires generally leave an Ash.)
Class B – Flammable liquids: gasoline, oil, grease, acetone
Any non-metal in a liquid state, on fire. This classification also includes flammable gases. (Class B fires generally involve materials that Boil or Bubble.)
Class C – Electrical: energized electrical equipment
As long as it’s “plugged in,” it would be considered a class C fire. (Class C fires generally deal with electrical Current.)
Class D – Metals: potassium, sodium, aluminum, magnesium
Unless you work in a laboratory or in an industry that uses these materials, it is unlikely you’ll have to deal with a Class D fire. It takes special extinguishing agents (Metal-X, foam) to fight such a fire.
Most fire extinguishers will have a pictograph label telling you which classifications of fire the extinguisher is designed to fight. For example, a simple water extinguisher might have a label like the one below, indicating that it should only be used on Class A fires.
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 determine the effect of oxygen in the rate of burning.
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 (manipulated variable) is the amount of oxygen that we make available to fire.
Dependent variable (responding variable) is the rate of burning. Rate of burning can be determine by the amount of heat produced or by the loss of fuel.
Controlled variables are temperature and air flow in your place of experiment.
Constants are the type of fuel, amount of fuel, and the method of burning.
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.
This is a sample hypothesis:
The rate of burning increases by any increase in the available oxygen. My hypothesis is based on my gathered information and observations. I have seen that oxygen tanks are used in torches used to melt glass or cut steel.
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: Effect of oxygen in the rate of burning
Introduction:
About 20% of air is oxygen. To test the effect of oxygen in rate of burning you can simply modify amount of air available to flame. In this experiment you burn five identical candles with different amounts of air available to each candle. You will then measure the weight loss of each candle.
Diagram in the right shows a candle burning inside an upside down metal can. There are 3 holes at the lower section for oxygen to enter and 3 holes on the upper section for hot gases to exit.
Thermometer can be mounted in two different positions both shown in the diagram. You will need four sets of this setup with different number of holes for this experiment. (Optional)
Procedure:
- Get 5 identical small candles and label them as “Control”, 1, 2, 3 and 4.
- Prepare four empty metal cans number them from 1 to 4. These cans will be used like a hood to restrict the access of candles to the air. You will later place them upside down over the candles. Make 6 holes on the sides of all cans close to the bottom of the can. (This will become close to the top when the cans are upside down). For can number one make one hole on the side close to the top. (This will be the lower hole when the can is upside down).
Make two of these holes for can number 2 and 3 for can number 3 and four for can number 4. (Diameter of each hole may be 3/16 of an inch or 5 mm). - Weigh each candle and record the initial weight of candles in your data table.
- Place each candle in the center of one metal or ceramic plate and secure it using some chewed gum.
- Add about 1/2 cm (1/5 inch) water to the bottom of each plate.
- Turn on all the candles, record the time and place cans number 1 to 4 upside down on candles number 1 to 4.
- After 1 hour remove the cans, turn off the candles and weigh the remaining candle. Record the weight of remaining candle in your table.
Following is how your results table may look like:
| Initial weight/ mass | Final weight | Weight loss | |
| Control | |||
| 1 | |||
| 2 | |||
| 3 | |||
| 4 |
Depending on the size of your candle, you may need to reduce or increase the duration of your experiment.
Note: Weight loss of candles, and the amount of produced heat are two different measures for the rate of burning. You must usually select one of these two measures for your experiment. You may choose to measure the weight loss of candles or the produced heat for your experiment.
Questions and answers:
Why do we put candles in metal plates and why do we add water in plates?
Metal plates are used for fire safety. Water is added so no air can enter from the edges of the can.
What size candle should I use?
Small candles are preferred. With small candles you can get a result in a shorter time.
How big the holes are supposed to be?
The diameter of each hole can be 3 millimeters or 1/8th of an inch. If shortage of oxygen kills the flame, increase the the number of holes. For example you may use 2, 4, 6 and 8 holes instead of 1, 2, 3 and 4 holes.
How do I make the holes?
This is where an adult must help. Holes can be made using a nail or using an electric drill.
Can I use something else instead of metal cans?
Metal cans here are being used as a container for air. Depending on the size of your candle, you may be able to make aluminum cylinders using aluminum foil. Just use another cup to form the foil like a cylinder.
Where can I get thermometers?
Thermometers can be purchased online or from science suppliers. Food thermometers and room thermometers can be purchased from general merchandize stores.
I cannot find thermometers. How else I can can compare the produced energy?
Instead of making holes on the bottom of the can, make holes on the side, close to the bottom. In this way you can place a few drops of water on the can (while it is upside down) and record the time it takes to evaporate that water. Faster evaporation means more heat.
Can I use paper cups instead of metal cans?
Pour some water at the top of the upside down cup and you can do this.
Can I use medical thermometers instead?
No they won’t work for science experiments and they are not for the range that you need. You need a thermometer that can show up to 100ºC.
Sample Experiment Images:
A short candle with aluminum casing is weighted and placed in the center of a ceramic plate with some water on that.
An upside down paper cup is used as a hood. 5 mL water is covering the hood (outside bottom of the cup). The water prevents burning of the cup and can be used to measure heat produced by burning of candle.
A piece of wax is placed on the center of water. The time it takes for the wax to melt is another indication of the heat produced by burning.
After the wax is melted, water starts to boil. Measuring the melting time of the wax eliminates the need to thermometer. You must only make sure that the same size wax is used for all cups.
In this example the number of holes at the lower part of the hood (for entering air) has been 2, 3, 4 and 5. Initial trial with one hole turned off the flame. That is why we started with 2 and more holes. The number of holes for exiting hot gases have been 6 for all cups.
Experiment 2: Rate of oxygen in air
In this experiment we intend to test and measure the percent of oxygen in the air. The first thing that comes to our mind and is suggested by some websites, is letting a candle burn all the oxygen in a container and loss of volume represents the amount of oxygen. But this is not right. First reason is that when oxygen burns, the same amount or more water vapors and carbon dioxide and carbon mono oxide gases are produced. So there will be no loss of volume of air. The other problem is that flame will also heat up the air and expands the air, so after burning stops, air contracts because it cools off.
The percentage of oxygen present in a quantity of air can best be measured by using wet steel wool. Steel wool will react with oxygen and rust.
Procedure: Wash the steel wool with methyl alcohol or a similar solvent to remove any grease. Rinse it with water and push it into the bottom of a test tube. Turn the test tube upside down in a cup of water.
In about 24 hours all the oxygen will be combined with the steel wool and become rusted iron (Iron Oxide). Whatever gas is left in the test tube is not oxygen. This is a fairly effective way of finding the percentage of oxygen in air.
To determine the percentage of oxygen in air, see what percent of test tube is filled with water.
Safety Precautions:
Do your experiments in a place away from furniture and other flammable materials. Do it as small as possible and try to use the largest metal tray that you can find. If you do not have a metal tray, you can cover a large plastic tray with aluminum foil. Have a bucket of water handy as a fire extinguisher. All these experiments should be supervised by an adult. Take some pictures and use the pictures for your display and reports.
Experiment 3: How does excess oxygen in the air affect the rate of burning
Introduction: Oxygen is the only gas in the air that is used in process of burning. In this experiment you will test the rate of burning of candles with and without excess oxygen in the air. Oxygen for this experiment can be purchased from medical suppliers. They will usually ask for a deposit so you will return the empty cylinders.
Procedure:
Get a small oxygen tank for this experiment. Use thick aluminum foil to make a funnel and connect the funnel to the nozzle of the oxygen tank. The purpose of this funnel is to distribute oxygen and reduce its speed.
Weight four candles for this experiment. Label them A1, A2, O1 and O2. (A is for air and O is for oxygen)
Place two candles labeled O1 and O2 close to the opening of the funnel and two other candles somewhere away from this setup.
Turn on all four candles and open the valve of oxygen tank to start a slow flow of oxygen. Observe and compare the color of flame in high oxygen area and the other two candles.
After one hour, close the oxygen and turn off all the candles. Measure and record the final weight of candles in your results table.
Your results table may look like this:
| Candles | Initial weight | Final weight | Fuel consumption |
| A1 | |||
| A2 | |||
| O1 | |||
| O2 |
Fuel consumption in the last column is the amount of candle wax consumed in one hour. To calculate that subtract final weight from initial weight of each candle.
Note: Your teacher may want to use the term mass instead of weight. Technically mass is a better term that shows the real amount of a substance. If that is the case, substitute the word weight by the word mass in this project guide.
Materials and Equipment:
This is a suggested list of material for experiment number 1:
- 5 small candles
- 4 metal cans
- Some tools for making holes
- Lighter
- 5 plates
- Any tool for measuring same amount of water (pipette, dropper, small graduated cylinder, …)
- Scale (to measure the weight of candles before and after the experiment)
- Thermometers for the range of 0 to 150ºC (optional)
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:
No calculation is required.
Summery 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.
References:
Visit your local library and find books related to “Fire” or “Chemistry of Fire”. Any of such books can be a good reference for this project.
