Carbon Dioxide

Deep Diving Raisins

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In the Exploring Density experiment, we looked at how different liquids have different densities, and how the different densities helped the liquids stay in separate layers, even when combined in the same container. In this experiment, we will explore how the density of an object can be altered without changing the object’s mass.

Before we begin, let’s review some key terms. Volume is how much space an object takes up. Mass is how much an object weighs. Density is the comparison of mass to volume. Something that doesn’t weigh that much but takes up a lot of space has low density. Something that doesn’t take up a lot space but weighs a lot has high density. In the previous comparison, we looked at a 1-pound bag of marshmallows vs. a baseball. Both have the same mass (or weight), but the baseball contains that mass in a much smaller volume (or space) than the marshmallows, so the baseball has a higher density.

If you can increase the volume of an object without increasing its mass, you will change its density. Imagine a balloon. If you weigh a balloon before you blow it up and weigh it again after you blow it up, you will see that the weight of the balloon increased only a little bit (due to the weight of the air inside the balloon), but the volume of the balloon increased dramatically. The uninflated balloon has a much greater density than the inflated balloon because the weight is confined to a much smaller space. Let’s try increasing the volume of something without increasing the mass at all!

The Experiment

Supplies: Two clear drinking glasses, eight raisins, tap water, a clear soda drink (club soda, 7-Up, etc.)

What to do: Fill one glass with water. Fill the other glass with the soda drink. Drop four raisins in each glass. Observe the raisins. What did the raisins in each glass do? How long did it take for the raisins to stop?

What is happening: When you first drop the raisins into each glass, they sink to the bottom of the glass because they have a greater density than the liquids they are in. The raisins in the glass of water do nothing, but the raisins in the soda begin to move after a short time. Raisins have a rough, dented surface. If you inspect the raisins in the water glass, you should see some air bubbles attached to each raisin. There are not enough bubbles on the raisins in the water glass to affect the raisins’ density, and there is no other source of bubbles in the water. Soda is carbonated, meaning it has carbon dioxide gas as one of its ingredients. Carbon dioxide gas is what makes soda “bubbly”. The soda releases carbon dioxide bubbles, and these bubbles attach to the rough surface of the raisins. The carbon dioxide bubbles increase the volume of each raisin, but the mass of each raisin stays relatively the same. When the volume increases but the mass does not, the overall density of the raisin is lowered. The raisins are now less dense than the soda, so they rise to the surface.

Once the raisins get to the surface of the soda, the carbon dioxide bubbles pop, causing the raisins’ density to change again, and they sink as a result. Once the raisins reach the bottom of the glass again, the process repeats itself, sending the raisins back toward the surface of the soda. The raisins will bob up and down for several minutes, until all of the carbon dioxide has escaped and the soda is flat. This experiment demonstrates how an increase in volume can lead to a decrease in density in an object, as long as the mass of that object is not significantly affected.

Take It Further

Try putting the raisins in a jar with a lid or directly into a bottle of soda. What happens to the raisins when you put the lid or cap back on? What happens when you take it back off? When put the raisins into a container and seal the container, the raisins will eventually stop the rising and sinking cycle. When it is in a glass, the carbon dioxide released by the soda can escape into the atmosphere. In a closed container, some carbon dioxide gets released, but it cannot leave the bottle, so pressure builds up in the space between the surface of the soda and the bottle cap. When you open the bottle, the hissing noise you hear is the built-up carbon dioxide escaping the enclosed space. As long as the cap is on the soda bottle, the contents of the bottle are under pressure. That pressure prevents carbon dioxide bubbles from forming, and any bubbles that do form cannot grow as large as they would in an open container or glass. Once the container is opened and the pressure released, then the bubbles are free to form again, and the raisins will resume their floating and sinking cycle!

Try this experiment with other dried fruits, like cranberries, or other small fruits or nuts, like grapes, blueberries, almonds, or peanuts. Are the results the same?

Links

To learn more about density, head to Kiddle Encyclopedia!

Discovering Oxygen

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As discussed in the Fire Extinguisher experiment, fire is a chemical reaction that requires a fuel source, heat, and oxygen in order to sustain itself. Without one or more of those components, the reaction will stop and the flames will go out. The combustion reaction consumes both the fuel and the oxygen and reorganizes their molecules into new substances, including carbon dioxide.

In a candle, the fuel source is actually the wax of the candle, not the wick. The heat from the flame melts the wax surrounding the wick. The wick “sucks up” the melted wax, like a drink through a straw, delivering it to the flame. The fire then burns the melted wax, creating more heat, which melts more wax. Traditionally, candles were made from substances found in nature that burned very slowly, like animal fats or beeswax. Today, candles can also be made with paraffin wax (a byproduct of oil refining) or plant oil-based waxes like soy wax. Wax burns much slower than other fuel sources, like wood, so candles can produce sustained light for a long period of time.

Have you ever wondered why a candle goes out when you blow on it? It is not because of the carbon dioxide in our breath. The current from blowing lowers the temperature of the area around the reaction and separates the flame from the fuel source – the melted wax. Without anything to burn and without the requisite heat, the reaction stops.

The Experiment

Supplies: A tealight candle, a saucer or shallow bowl, water, food coloring (optional), a clear glass or jar, a lighter or match, an adult helper.

What to do: Ask your adult assistant to set the candle in the saucer and light it. Add a few drops of food coloring to your water, if desired. Pour about 1/4 cup of water into the saucer so that it surrounds but does not extinguish the candle. Turn the glass upside down and carefully place it over the candle. What happens to the candle? What happens to the interior surface of the glass? What happens to the water in the saucer? Listen carefully as you lift the glass up.

What is happening: Three different principles are being demonstrated in this experiment. The first has to do with the mechanics of the chemical reaction. The water forms a seal between the upside-down glass and the dish, limiting the reaction to only the air available inside the glass. At first, the candle will continue to burn as normal, but the longer the flame burns, the less oxygen is available in the confined space to sustain the reaction. The candle will only burn as long as there is oxygen inside the jar.

The second thing happening inside the glass is proof the the displacement reaction taking place. In displacement reactions, the compounds or molecules that contribute to the reaction are different than the ones that result from the reaction. In this case, the carbon and hydrogen from the wax is combining with the oxygen to fuel the reaction. The during the reaction, the oxygen molecules get shifted around, and the end products of the reaction are carbon dioxide gas and water. While the flame is burning, the water remains in the air inside the glass in the form of water vapor, but as soon as the flame goes out, the air inside the glass cools down, and the water vapor condenses on the interior surface of the glass.

Did you notice the water creeping up the sides of the glass as the flame went out? This is related to the third principle being demonstrated, differences in air pressure. While the flame was burning, the oxygen inside the glass was being consumed by the reaction and replaced with carbon dioxide, but not in equal quantities. The heat from the flame causes the gas inside the glass to expand in volume, but once the flame goes out, the gas inside the glass cools down quickly. This creates a vacuum inside the glass because the air pressure outside the glass is greater than the air pressure inside the glass. The sound created when you moved the glass was the greater outside air pressure rushing in to fill the space inside the glass where the air pressure was lower.

Links

To learn more about oxygen and Antoine Lavoisier (the scientist who came up with the name “oxygen” and made this experiment famous), head to the Kiddle article on Oxygen Facts.

Make a Fire Extinguisher

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Did you know that fire is a chemical reaction? Fire is the most common form of a combustion reaction. Combustion, or burning, describes an interaction of oxygen and a fuel source that results in heat and light, usually in the form of a flame. Combustion combines the fuel source and oxygen to create an exothermic reaction, a reaction that generates heat above and beyond the heat needed to initiate the reaction.

In order to have a combustion reaction, the fuel and oxygen need a catalyst. A catalyst is something that causes or speeds up a chemical reaction without itself being altered. The catalyst for a fire is usually temperature. The fuel has to reach a certain temperature and be in the presence of oxygen before it will ignite. Because fire is an exothermic reaction, a single spark (which can reach temperatures over 2,000 degrees!) is hot enough to begin the combustion process, and the expelled heat is enough to keep the reaction going.

Without all three ingredients – fuel, oxygen, and heat – a combustion reaction is not possible. A fuel source like paper or wood, in the presence of oxygen but without heat, will not ignite all by itself. If it did, trees and papers would be constantly burning! Likewise, having fuel and heat might ignite a reaction, but without oxygen, the reaction cannot be sustained. That is the principle we will examine in this experiment.

The Experiment

Supplies: Baking soda, a shallow bowl, a tea light candle, vinegar, a lighter or match, and an adult helper.

What to do: Sprinkle some baking soda in the bottom of the bowl. Make sure you use enough to create a nice, even layer. Set the tea light in the middle of the bowl. Ask your adult helper to light the candle. Slowly and carefully pour the vinegar into the bowl, making sure not to splash or extinguish the candle as you pour. What happens to the baking soda? What happens to the candle?

What is happening: Combining vinegar and baking soda causes a chemical reaction. One of the products of that reaction is carbon dioxide, which is a heavier gas than the oxygen/nitrogen combination in the air. The carbon dioxide settles at the bottom of the bowl, displacing the oxygen surrounding your candle. Without oxygen, the reaction cannot be sustained and the flame goes out.

Links

For an overview on combustion, check out this article on Britannica Kids.

For more in-depth information, Mocomi examines different types of combustion, flames, and fuels.

To learn more about how fire extinguishers work to put out flames, the journalists at The Conversation answers questions from Curious Kids.

Orange Fizz

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As demonstrated in the Make Carbon Dioxide experiment, acids and bases do not play well together. That experiment used vinegar and baking soda to create a reaction. In this experiment, the vinegar is replaced with something a little more mild (and tasty) – citric acid.

Citric acid is an acid found in citrus fruits like lemons, limes, grapefruits, and oranges, and in other fruits and vegetables like strawberries, raspberries, and tomatoes. It is a safe acid, and it’s what gives oranges, lemons, and limes their tartness. Different citrus fruits have different concentrations of citric acid. Lemons and limes have high concentrations, while oranges and grapefruits have lower concentrations. The higher the concentration of citric acid, the more sour-tasting a fruit will be. That is why lemon juice tastes sour and zingy while orange juice tastes sweet and tangy.

The Experiment

Supplies: an orange or clementine (cutie), some baking soda

What to do: Cut the orange into wedges or peel & separate into slices. Take a bite of the orange all by itself. Dip a second slice LIGHTLY into the baking soda. Take a bite. As you chew, it should start to bubble in your mouth. It might even taste like orange soda!

What is happening: Oranges and other citrus fruits contain citric acid. Baking soda is a base, the opposite of an acid. It is safe to eat but doesn’t taste very good on its own. As the citric acid and baking soda mix, it makes millions of carbon dioxide bubbles, the same gas you breathe out, and the same one that makes soda so fizzy.

Take it a step further: Try repeating this experiment using different fruits and vegetables. Compare what the flavors taste like and how fizzy the reaction is in your mouth. Did the juice fizz more or less that others you tried? Is there a relationship between how fizzy the bite with baking soda was compared to how sweet or sour the plain bite was?

Links

To see this experiment in action, head to YouTube and explore Science Fun for Everyone.

Make Carbon Dioxide

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Carbon dioxide is a clear, odorless gas that occurs naturally in our environment. It is one of the most important gases on Earth because it is one of the components necessary for plant survival. Trees and plants need carbon dioxide and water to make their own food, and they give off oxygen in the process. Humans need the oxygen to breathe and many of our food sources are from plants, so with out plants, we would suffocate and starve! Just like plants take in carbon dioxide and give off oxygen, humans take in oxygen and give off carbon dioxide. This kind of mutually beneficial relationship is called symbiosis.

Chemistry is the study of different substances and how they interact. Chemical compounds fall into different categories, depending upon where they fall on the pH scale. pH stands for “potential of hydrogen,” and the pH scale measures how much hydrogen is contained within any given compound. Vinegar is an acid. Acids fall below 7 on the pH scale. They tend to have a sour taste and can cause a burning sensation in nasal passages when smelled. Acids are sticky and react with with metals. Baking soda is a base, meaning that it falls above 7 on the pH scale. Bases are generally odorless and have a bitter taste. They tend to be slippery and they react with fats and oils. Water is neutral, meaning it falls right in the middle of the pH scale at 7. When acids and bases combine, the reaction is a volatile one, but the acids and bases can balance each other out, resulting in compounds that are closer to neutral. This experiment will combine common substances to create an interaction that will produce carbon dioxide. Carbon dioxide, or CO2, is the same gas that is used to make soda fizzy, so releasing CO2 can cause bubbles!

The Experiment

Supplies: a tall glass, baking soda, vinegar, liquid dish soap, tap water, food coloring (optional).

What to do: DO THIS EXPERIMENT OUTSIDE OR IN THE SINK. Fill the glass half full of water. Add a tablespoon of baking soda and five drops of detergent. Add 2-3 drops of food coloring, if you want. Stir well to combine ingredients. Last, add a quarter cup of vinegar. What happened when the vinegar was added?

What is happening: Water has hydrogen and oxygen as its elemental building blocks. Baking soda and vinegar both have carbon, hydrogen, and oxygen, but the proportion of “ingredients” in each of these chemical compounds is different. Baking soda also has a fourth ingredient – sodium. When all the atoms from all the compounds are allowed to combine, they react violently. The bonds holding the atoms of each compound break, allowing the atoms to reorganize into new compounds. The hydrogen from the vinegar interacts with the sodium and the carbon from the baking soda and forms two new substances – sodium acetate (a salt) and carbonic acid (a liquid). Carbonic acid is highly unstable, so even as the carbonic acid is being formed, it is also breaking apart. Immediately the atomic bonds in the carbonic acid break down, resulting in liquid water and carbon dioxide gas. The gas is lighter than the water, so it moves upward through the liquid in the form of bubbles!

Links

For a more detailed discussion of this experiment, visit the Wonderopolis website.