Maddie James
A simple experiment can be performed to demonstrate the effect of dry ice gas on a candle flame. Dry ice, which is solid carbon dioxide, sublimates at a temperature of -78.5 °C, and is denser than air. When dry ice gas is poured into a vessel containing a lit candle, the flame is extinguished as the carbon dioxide displaces the oxygen in the air surrounding the candle. This is because a candle requires three things to sustain a flame: fuel, oxygen, and heat.
| Characteristics | Values |
|---|---|
| Density of oxygen at 25°C | 1.31 g/L |
| Density of carbon dioxide at -78.5°C | 1.56 g/L |
| Candle combustion requirements | Fuel, oxygen, and heat |
| Carbon dioxide sources | Solid carbon dioxide (dry ice), baking soda and vinegar, hydrochloric acid and marble chips |
| Candle flame reaction | Carbon dioxide poured over it will extinguish the flame |
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What You'll Learn
Carbon dioxide is denser than air
The experiment can be further enhanced by using a clear container and placing multiple candles at varying heights within it. As carbon dioxide gas is poured into the container, the candles will be extinguished one by one from the bottom up. This sequential extinguishment occurs because the denser carbon dioxide gas displaces the oxygen from the bottom of the container upwards, showcasing its higher density compared to air.
Additionally, the experiment can be adapted to use chemical reactions to generate carbon dioxide gas. By adding hydrochloric acid to marble chips, a steady stream of carbon dioxide is produced, which can then be collected in a flask. This carbon dioxide gas is heavier than air, and when poured out, it will sink and displace the oxygen-containing air, similar to the behaviour of a liquid. This behaviour reinforces the concept that carbon dioxide gas is denser than air and can effectively suffocate a flame by displacing the oxygen required for combustion.
The principle that carbon dioxide is denser than air has practical applications, particularly in fire safety. Carbon dioxide fire extinguishers utilise this property to suppress fires by displacing oxygen and creating a barrier that prevents the fire from accessing the oxygen necessary for combustion. This method of fire extinguishment is particularly effective for liquid and gas fires, where the carbon dioxide also helps to cool the fuel and further inhibit combustion.
In summary, the statement "carbon dioxide is denser than air" forms the basis for various experiments and applications. By understanding the behaviour of carbon dioxide gas and its ability to displace oxygen, we can not only perform intriguing science demonstrations but also develop practical tools, such as carbon dioxide fire extinguishers, that leverage this unique property to our advantage.
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The candle's combustion process
The combustion process of a candle is a fascinating chemical reaction. When a candle is lit, the heat of the flame melts the wax near the wick. This liquid wax is drawn up the wick by capillary action. The flame then vaporizes the liquid wax, turning it into a hot gas. At this stage, the hot gas breaks down into molecules of hydrogen and carbon. These molecules are drawn into the flame, where they react with oxygen from the air. This reaction produces heat, light, water vapour, and carbon dioxide.
The combustion process of a candle requires three key components: fuel, oxygen, and heat. The heat from the flame sustains the reaction, keeping it above the temperature required for combustion. The wax vapour around the wick is essential to maintaining the flame. If the heat is removed, the wax drops below the required temperature, causing the flame to extinguish. However, if a lit match is brought close to the wick, the flame will ignite again.
When dry ice gas, which is carbon dioxide, is introduced to a burning candle, it affects the combustion process by displacing oxygen. Carbon dioxide is denser than oxygen, so when released, it sinks and pushes oxygen-containing air upwards. As the candle flame loses access to oxygen, one of its key fuel sources is eliminated, causing the flame to go out. This occurs even if the wax vapour and heat are still present.
The density difference between carbon dioxide and oxygen is what makes this experiment work. The denser gas displaces the oxygen, extinguishing the flame. This principle is also why carbon dioxide is used in some fire extinguishers.
In conclusion, the combustion process of a candle relies on the interaction of heat, wax, and oxygen. The introduction of dry ice gas disrupts this process by removing the oxygen element, demonstrating the importance of each component in sustaining the flame.
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How to generate carbon dioxide chemically
Carbon dioxide is a colourless, odourless gas composed of one atom of carbon and two atoms of oxygen. It is easy to create using common household chemicals such as baking soda and vinegar. The basic baking soda reacts with the acidic vinegar to release water, sodium acetate, and carbon dioxide. The gas produced can be harvested and used for experiments, such as blowing out a candle.
To generate carbon dioxide chemically, you will need the following:
- Vinegar
- Baking soda (also known as sodium bicarbonate or bicarbonate of soda)
- A container (such as a glass or a bottle)
- A candle
- Optional: a balloon
Step 1: Pour about one inch of vinegar into your container.
Step 2: Slowly add two tablespoons of baking soda to the container. You should see the mixture start to fizz and bubble. This reaction between the vinegar and baking soda produces carbon dioxide gas.
Step 3: Continue adding small amounts of baking soda until there is no more fizzing. The carbon dioxide being produced is heavier than air, so it will sink and remain in the container.
Step 4: Optional: Capture the carbon dioxide gas in a balloon by stretching the neck of the balloon over the container's opening.
Step 5: Light a candle.
Step 6: Pour the carbon dioxide from the container onto the candle flame. Alternatively, pour the carbon dioxide from the balloon over the candle. The carbon dioxide will extinguish the flame as it is heavier than air and will displace the oxygen fuelling the flame.
Dry Ice and Candles
Dry ice is solid carbon dioxide. When dry ice melts, it goes directly from a solid to a gas (a process called sublimation) and produces carbon dioxide gas. When this gas hits a candle, it extinguishes the flame in the same way as the chemically produced carbon dioxide. The gas is poured towards the flame, where it displaces the oxygen, acting as a suffocant and putting out the fire.
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Safety precautions when handling dry ice
When dry ice gas is poured into a vessel containing a lit candle, the candle is extinguished. This is because carbon dioxide is denser than air and cannot support combustion. However, handling dry ice can be dangerous, and there are several safety precautions to be aware of:
- Protective clothing: Dry ice can cause burns and frostbite, so protective clothing is essential. Cryogenic gloves must always be worn when handling dry ice, and eye protection in the form of safety glasses, goggles, or a face shield is also necessary.
- Ventilation: Carbon dioxide is a simple asphyxiant, and poor ventilation can lead to depletion of oxygen levels and asphyxiation. Always store and handle dry ice in a well-ventilated area, and never place your head inside a cooler containing dry ice, as the heavy vapors can settle in low-lying places.
- Explosion risk: Never place dry ice in a sealed or tightly closed container. Sufficient gas buildup can occur, leading to an explosion. Do not place dry ice in ultra-low freezers, refrigerators, closets, cabinets, or other enclosed spaces.
- Storage: Dry ice must be stored in a suitable container, such as a Styrofoam chest, insulated cooler, or a special cooler designed for dry ice storage.
- Disposal: Never dispose of dry ice in a sink, toilet, drain, trash, or garbage. Allow unused portions to sublime in a well-ventilated area.
- Flammables: Keep flammables away from open flames when handling dry ice.
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Why the flame is extinguished
When dry ice gas hits a candle, the flame is extinguished because carbon dioxide is denser than oxygen. As the carbon dioxide gas is poured into a vessel containing a lit candle, it sinks and displaces the oxygen-containing air surrounding the flame. This suffocates the flame, causing it to go out.
To understand why the flame is extinguished, it is important to know that a candle needs three things to sustain a flame: fuel, oxygen, and heat. The heat overcomes the energy needed for the combustion reaction. If you remove the heat, the flame cannot sustain itself. When you blow on a candle, you force the heat away from the wick, causing the wax to drop below the temperature required for combustion.
In the case of using dry ice gas, the carbon dioxide acts as a heavier gas that displaces the oxygen required for the candle's combustion. The carbon dioxide, being denser than oxygen, sinks and pushes the oxygenated air upwards and out of the container. As the oxygen around the flame is removed, the flame is deprived of one of its essential elements and is, therefore, extinguished.
Additionally, carbon dioxide cannot support combustion. When a candle burns, the heat of the flame melts the wax near the wick, and this liquid wax is drawn up the wick. The flame then vaporizes the liquid wax, breaking down the hydrocarbons into molecules of hydrogen and carbon. These vaporized molecules react with oxygen to produce heat, light, water vapour, and carbon dioxide. However, when carbon dioxide is poured onto a flame, it cannot support combustion, and the flame is extinguished.
The density difference between carbon dioxide and oxygen is significant. At 25°C, oxygen has a density of 1.31 g/L, while carbon dioxide has a density of 1.56 g/L at -78.5°C. This difference in density is why carbon dioxide displaces oxygen and extinguishes the flame when poured into a container with a lit candle.
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Frequently asked questions
The candle will be extinguished as carbon dioxide is denser than air and displaces the oxygen that the flame needs to burn.
Dry ice should never be touched directly and protective gloves and eye protection should be worn when handling it. It should also not be placed in a sealed container.
Place a piece of dry ice inside a cup or flask near a lit candle. The dry ice will sublimate, turning from a solid to a gas, and fill the cup or flask with carbon dioxide. The carbon dioxide will then pour out of the cup or flask and extinguish the candle.
