Vinegar

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.

Green Pennies

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As discussed in the enzyme experiment, chemical reactions occur when separate atoms or molecules interact and combine their molecular building blocks to create new and different compounds. The addition of enzymes to a reaction will speed the reaction up, but even without the enzyme, the reaction will still occur. It will just take a little more time.

Displacement or Replacement Reactions are those that when molecules from one substance or compound change place with molecules from another substance or compound, forming a third, different substance or compound. Oxidation is a good example of a replacement reaction. When iron interacts with water and oxygen, the oxygen from the air and the water combines with the iron to form iron oxide (rust). Other molecules present in the air and the metal will combine with the hydrogen to produce an acid. This acid seeps into the microscopic spaces in the iron and opens them up, like tunnels, to allow more oxygen to penetrate into the metal, allowing the metal to oxidize even further. Left alone for a long period of time, the iron can be completely oxidized, until there is nothing but rust left.

In this experiment, we will create a displacement reaction on the surface of a penny.

The Experiment

Supplies: Paper towel, four or five pennies, vinegar, and a non-metal saucer or bowl. A plate with a raised edge or a shallow baking dish works well. Dark or “dirty-looking” pennies may work better than bright shiny ones. Try to use an assortment of pennies, if possible.

What to do: Fold the paper towel in half and fold again into a square. Place the paper towel in the dish. Pour enough vinegar onto the paper towel to thoroughly wet it, but without creating a pool of vinegar. Place the pennies on the paper towel and fold the towel loosely over onto the pennies. Wait 24 hours. Observe what happens. What happened to the pennies? What happened to the paper towel?

What is happening: Modern pennies have a zinc core and a copper alloy exterior, while older pennies are entirely copper alloy. Alloy is just a fancy word meaning a mixture of metals, and “copper alloy” means that the main metal in the mixture is copper. The dark, dirty-looking material on the dingy pennies is actually copper oxide (copper’s version of “rust”). The vinegar penetrated the copper oxide and disolved it slightly (decomposition reaction), freeing the copper to interact with the oxygen in the air. The copper, vinegar, and air combined to create copper acetate, which is green. The copper acetate is a substance completely separate from the penny, the paper towel, and the vinegar. This explains why it was able to settle onto both the paper towel and the penny.

Left on its own, copper will eventually change in appearance, from its shiny orange-red color to the green that appeared on the pennies. When construction began on the Statue of Liberty, back in 1875, Lady Liberty was not the dull, pale green she is today. She was shiny and orange-red, like a new penny. Exposure to the air, combined with acid rain (rain containing pollutants that lower the pH of the water, causing it to be slightly acidic), has caused a patina (surface discoloration) of copper acetate to form on the statue’s surface. This infographic demonstrates the color change over time. Notice how, during the first several years, the color of the statue was closer to that of an old penny?

The Statue of Liberty is almost 150 years old. She has aged quite nicely!

Links

For a variation in this experiment, head to The Exploratorium. Their experiment, involving pennies, vinegar, and salt, actually creates free-floating copper in the vinegar!

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.