Key Concepts
Chemistry
Chemical reactions
States of matter
Combustion
Introduction
There are many occasions to light candles. Have you ever looked closely at the flame? Which part of the candle is actually burning? Can you tell? Is it the wick, the solid wax, the liquid wax or something else? In this activity you will light some candles to find out—no special occasion required!
Background
Whether they are on a birthday cake or dinner table or menorah, most candles we use today are wax-dipped candles. This style of candle dates back to the ancient Romans. Through the center of the wax runs a wick, which is usually made from cotton or other material that can absorb liquids well. So how do these two materials come together to help a candle burn steadily?
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A lit candle might seem simple, but it is actually an example of a multi-step process resulting in combustion—and the glowing flame you see. Combustion is the result of a chemical reaction in which oxygen gas reacts with the substance that is being burned. The combustible material in a candle—or its fuel—is the wax. But before the wax can become fuel it first needs to get hot enough. To start that heating process, you first need to light the wick with another source of fire, such as a match. As the wick burns down the heat of the flame melts the wax around the wick. Because the wick is absorbent it sucks the liquid wax into the wick and upward into the flame. Once the liquid wax gets hot enough, it then turns from a liquid into a gas. The hot gas then reacts with the oxygen from the air and is burned, creating the candle flame that we see. This means that the candle flame is actually created by the burning wax gas—or vapor—and not by the wick itself or the solid or even liquid wax.
After lighting a candle, it might flicker or sputter at first, but then it usually burns fairly steadily. As the heat of the wax vapor flame melts more of the solid wax it creates more fuel for the flame to burn. The candle will only go out once it runs out of wax or oxygen—or gets blown out. After a candle goes out you can actually see the wax vapor escaping as a stream of white smoke. If you hold a match into that smoke, the candle will catch fire again—without even touching the wick! Don't believe it? Then try this activity to see for yourself!
Materials
Adult helper
Several small, narrow, birthday candles
Matches or a lighter
Wet sand (or another non-flammable substance to hold your candles up—you could also use cake or a cupcake!)
Dish or bowl for your wet sand or other candle-holding substance
Fireproof work area
Straw
Bowl filled with water or a fire extinguisher
Preparation
Take your materials to a fireproof work area.
Make sure you have an adult helper assist you while doing this activity.
Keep the bowl of water or the fire extinguisher close throughout the activity in case you need it.
Prepare your wet sand or other non-flammable base material in the dish or bowl.
Stand one candle up in your wet sand or other material, packing it around the candle base to make sure it is secure.
Procedure
With the help of an adult, light a match. Hold the flame close to the candle's wick, but don't touch the wick with the flame. What do you observe? Does the candle light?
Next touch the candle's wick with the flame of the match. Hold it there for about a second. What happens when you touch the wick with the flame? If the wick did not ignite, light it now.
Watch the candle burn for a couple of seconds. Can you describe the flame? How does it look?
Blow out the candle and watch what happens. Do you see white smoke escaping from the wick?
Light the candle again then light another match. While the match is still burning blow out the candle. Immediately afterward hold the flame of the match into the white smoke of the blown-out candle, close to the wick but without touching it. What happens? Does the candle light again? Why or why not?
Blow out the burning candle. Now stand two candles next to each other in your wet sand (or other material) so that they are secure and will not fall over. They should almost touch each other. Light both candles with a match.
While both candles are burning point the end of a straw to one of the flames. Blow through the straw to extinguish just one of the flames. The other candle should keep burning. What happens after you extinguish one of the candles? Can you explain your observation?
Repeat this step several times. Do you always get the same results? Can you tell from your observations which part of the candle is burning? Why?
Extra: Place three or more candles next to each other. With a straw, blow out one of the candles, but keep the others burning. What happens to the blown-out candle? Then blow out two of the candles but keep one burning. Can you see the flame jumping from one candle to another?
Extra: Try the activity with candles made of paraffin or beeswax. Do you get the same results for these materials as well?
Extra: Look at a candle's flame in more detail. Can you see that the flame has different colors? Do your own research to find out why there are different colors. Can you find out which part of the flame is the hottest or coolest?
Observations and Results
Could you make a candle's flame jump from one candle to another? The first time you lit your candle you most likely had to touch the wick with the flame of your match. This makes the wick catch fire, which starts the combustion reaction. The wax around the wick starts melting, and it is from this liquid wax that vapor is created inside the flame. The wax vapor starts to burn and creates the stable candle flame that you see. When you blew out the candle you should have seen white smoke rising up into the air from the wick. This is the wax vapor, which becomes visible as it condenses into small liquid droplets in the cooler air.
If you touched the wax vapor (white smoke) with another flame, the candle should have immediately lit up again. This time you didn't even have to touch the wick or another part of the candle. Lighting the vapor is enough to get the candle burning again. When you placed two or more candles next to each other and blew one out the burning candle's flame should have reignited the wax vapor of the extinguished one. You might have realized that it is actually quite hard to keep a candle extinguished when it is so close to a burning one. It lights up again due to the fact that the wax vapor of the blown-out candle is touching the remaining candle flame. What you end up seeing is the candle flame jumping from one candle to another!
Cleanup
Make sure to extinguish all your candles at the end of your experiment. Once the matches are cooled down, you can throw them in your regular trash. Clean up your work area and wash your hands with soap and water.
More to Explore
Candle Science, from the National Candle Association
Flame Out, from the American Chemical Society
Fire-Fighting Foam, from Scientific American
A Candle Seesaw Balancing Act, from Scientific American
STEM Activities for Kids, from Science Buddies
This activity brought to you in partnership with Science Buddies
