Creative Chemistry

Water That Coin

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There is an adage that says, “Like attracts like.” It basically means that similar things tend to stay together. It is possible to witness this in action simply by dropping water onto a penny.

The Experiment

Supplies: A paper towel, a penny, a small glass, an eye dropper or pipette, tap water.

What to do: Wash the penny well with soap and water. Make sure to dry it thoroughly. Set the penny flat on the paper towel. Fill the glass with water. Use the pipette or eye dropper to remove some water from the glass. Carefully place drops of water onto the penny, one at a time. How many drops of water can you place onto the penny before the bulge of water runs off the coin?

What is happening: As you place the drops of water onto the coin, you should see the water forming a small, dome-shaped bulge or bubble. Eventually, the bubble will “burst”, causing the water to run off over the edge of the penny.

The water bubble is a result of two things – cohesion and surface tension. Cohesion is when particles of the same substance stick together – “like attracting like”. Water molecules behave sort of like a bar magnet. They have a positive end and a negative end. The positive end of one water molecule is drawn to the negative end of the next water molecule. This cohesion draws the molecules tightly together, forming the dome-shaped bubble.

The outside of the bubble has surface tension. The attractive force exerted upon the surface molecules of the water by the molecules beneath tends to draw the surface molecules into the bulk of the water and makes the water assume the shape having the least surface area. In other words, the cohesion of the molecules is trying really hard to make the surface of the water (that area of the bubble where the water molecule has no neighboring molecule to cling to) as small as possible. The molecules on the surface are more attracted to the other water molecules than they are the air molecules around them, so they form a bubble. As long as the surface tension is greater than the force of gravity, the bubble will remain intact on top of the penny.

Take It Further

If you repeat this test several times, you will discover that the number of drops you can put on the penny each time changes. This is because the water you are using is changing each time. When an element of an experiment can change, that element is called a variable, because it can vary from test to test.

Try repeating this experiment using different variables. Some options include changing the type of coin you are using. Try it on a nickle, a dime, and a quarter. What do your results look like when comparing water on coins with smooth edges vs. water on coins with ridged edges? Another variable could be the liquid. What happens if you use bottled water instead of tap water? What about using salt water? You could also try using other liquids, like soda, fruit juice, or vegetable oil. You can also try rubbing alcohol or hydrogen peroxide. Just remember, if you are going to change a variable, make sure you only change one thing at a time. That will allow you to identify how the change in variable alters your results.

Links

To see this experiment in action, watch this video from Sick Science!
To explore more about cohesion and adhesion of water, visit Khan Academy.

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.

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!

Discovering Enzymes in Chemical Reactions

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Our world is constantly changing, as are the things in our world. Some changes that occur are the result of chemical reactions. A chemical reaction is when substances interact with one another resulting in all the substances being changed into something entirely new. Chemical reactions occur all around us, and even inside of us, every day!

There are different kinds of chemical reactions. Synthesis is when two or more different substances combine to make something completely new, like hydrogen and oxygen combining to become water. Decomposition is just the opposite. A complex substance breaks apart into it’s separate ingredients. Sea salt, used in cooking, is “made” by capturing salty ocean water and allowing the water to evaporate until all that is left is the salt (see our Evaporation experiments to learn about the water cycle). There are other types of chemical reactions that involve replacing or exchanging components, called displacement reactions. The illustration below shows how the different components interact.

Chemical reactions can be affected by other substances or variables (like reaction conditions), even if those things aren’t part of the reaction. Inhibitors slow down reactions, while catalysts speed them up. Temperature is a variable that can act as either an inhibitor or a catalyst. Cold temperatures often slow reactions down, while warmer temperatures have a tendency to speed things up.

Enzymes are biological molecules that act as catalysts in chemical reactions. There are wide range of enzymes that occur naturally in the human body that help the mechanics of our body to work. Our digestive system is full of enzymes, all designed to help convert the food we eat into the individual components our bodies need to function. One of the things that make enzymes special is that, even after the chemical reaction is over, the enzymes still remain, unchanged, ready to assist with the next reaction. In this experiment, we will examine an enzyme called catalase found in potatoes.

The Experiment

THIS EXPERIMENT REQUIRES COOKING AND THE USE OF A KNIFE. ADULT SUPERVISION IS RECOMMENDED.

Supplies: Hydrogen peroxide, a potato, 5-6 glasses or bowls, water, a knife and a cutting board, small saucepan, a spoon for adding and removing potato pieces from the glasses.

What to do: Peel and dice the potato into 1″ cubes. Add about 1/3 of the cubes to the saucepan. Add enough water to completely cover the potatoes. Cook over medium heat until the cubes are tender, about 10-15 minutes. Remove the potatoes from the heat, drain, and set aside to cool. Fill two glasses with water and four glasses with hydrogen peroxide. Make sure there is enough liquid to completely cover the potatoes once they are added. Take one raw potato cube and cut it into 4 smaller pieces. Add potato pieces to the glasses as indicated in the chart below. Observe the results.

#1#2#3#4#5#6
WaterWaterHydrogen PeroxideHydrogen PeroxideHydrogen PeroxideHydrogen Peroxide
1 Raw Potato cube1 Cooked Potato cube1 Raw Potato Cube1 Cooked Potato cube4 Small Raw Potato cubesSave for Round 2
(Control)(Control)

The pieces of potato in the glasses with water are there to provide a comparison. There should be no reaction that takes place in either of those glasses. Once the reaction in glass #3 has subsided, remove the potato cube and examine it. What does it look like compared to the potato piece from glass #1? After you have finished the visual inspection, add the potato piece from glass #3 to glass # 6. What happens?

What is happening: Raw potatoes contain an enzyme called catalase. Catalase is found in almost all living organisms, including people. Its job is to help speed up the decomposition of hydrogen peroxide (which can be harmful) and convert it to water and oxygen gas. The bubbles that were formed in the glasses with the raw potatoes contained oxygen gas. Just as catalase helps decompose the peroxide, heat breaks down the catalase, which is why the glass with the cooked potato piece had no reaction. Cutting the potato into smaller pieces created more exposed surfaces, giving the peroxide more opportunity to interact with the catalase. The reaction in glass #3 ended when the catalase had decomposed as much of the hydrogen peroxide as it could. Even though the potato was drastically altered visually, it still contained the catalase enzyme, which is why it could cause another reaction when added to glass #6.

Take It a Step Further

Catalase is present in almost all living organisms, so why not try this experiment with other fruits and vegetables? If you do, you can omit the cooking part, as you already know that heat degrades the catalase and makes it ineffective. The more bubbles you get in your reaction, the greater the amount of catalase present in that food. Which foods produced more bubbles? Which produced fewer bubbles?

Links

Cool Kid Facts has a great page that discusses chemical reactions and goes into more detail about some of the different kinds of reactions, including photosynthesis and combustion (did you know fire is a chemical reaction?!).

Education.com replicates this experiment, but uses raw, cooked, and frozen potatoes to compare how temperature affects the catalase. You can check it out here.

For a detailed examination of this experiment using a sweet potato and a variety of different liquids, including ammonia and vinegar, check out this chemistry class report. They have some pretty interesting pictures!

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.

Exploring Density

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Density describes the relationship between a substance’s mass, or weight, and its volume, or how much space it takes up. Things that are more dense take up less space than things with less density. To visualize density, let’s compare baseballs and marshmallows. A regular baseball weighs about one pound. It is small and compact and fits in the palm of your hand. A 16 oz. bag of marshmallows also weighs one pound, but because there is more air incorporated into the marshmallows, they are less dense. One pound of marshmallows takes up a lot more space, or volume, than a one-pound baseball.

When you combine substances that have different densities, the substances with the greatest density tend to move toward the bottom, while those with lesser densities tend to rise to the top. Gases tend to be lighter and less dense than liquids. Liquids tend to be lighter and less dense than solids. Even within these groups, there are a variety of densities.

The Experiments

Simple Experiment

Supplies: A clear jar with a lid, vegetable oil, water, food coloring (optional).

What to do: Fill the jar about half-full with water. Add food coloring, if desired. Pour in vegetable oil until the jar is almost full. Put the lid on the jar and MAKE SURE IT IS TIGHT. Give the jar a good shake so that the water and oil are thoroughly mixed. Set the jar where it won’t be disturbed and observe the liquid.

What is happening: The oil is less dense than the water, so it rises up to “float” on the surface of the water. The water and oil do not mix because of the molecular properties of each compound. Water molecules tend to want to “stick” to other water molecules, while oil molecules tend to want to stick to other oil molecules. This is because of something called molecular polarity, where the structures of the two molecules are not compatible. They push each other away, similar to a pair of magnets that won’t stick together. The longer the jar sits, the more the water and oil will sort themselves out, until they are completely separate again.

Complex Experiment

Supplies: A large jar or clear glass cylinder, liquid measuring cup with pour spout, a turkey baster, different colors of food coloring, honey or molasses, light corn syrup (Kayro), blue liquid dish soap, rubbing alcohol, yellow corn oil, water.

What to do: Pour 1 cup of honey or molasses into the bottom of your jar. Measure out 1 cup of light corn syrup and add some red food coloring. Stir until well combined. Carefully pour the corn syrup into the jar, making sure to avoid hitting the sides of the jar. Measure out 1 cup of dish soap. Slowly add the dish soap, again avoiding the sides of the jar. Measure out 1 cup of water and add to the jar, but this time use the turkey baster to slowly drizzle the water down the side of the jar. Measure out 1 cup of corn oil and add to the jar, again using the turkey baster. Finally, measure out 1 cup of rubbing alcohol. Add green food coloring and stir well. Add the rubbing alcohol into the jar using the turkey baster.

What is happening: Different liquids have different densities. Liquids like honey and dish soap are more dense than water, while other liquids, like rubbing alcohol and vegetable oil are less dense and will float above the water. Adding the food coloring helps distinguish the different layers. The various densities of the different liquids is what keeps the layers separate.

Links

You could take the Density Column experiment one step further by dropping in solid objects to see where they land, OR you could just watch this great video from the Bearded Science Guy.

Blobs in a Bottle

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If you have ever seen a lava lamp, you know how mesmerizing it is to watch the blobs rise and sink through the liquid. Most lava lamps contain a combination of water and wax. As a solid, wax is heavier than water and will sink to the bottom of the container. When wax melts into a liquid, it is lighter than water and will rise or float on top of the water. A lava lamp works by having a heat source at the bottom of the lamp to melt the wax. The melted wax rises through the water, but then sinks as it cools off and begins to harden again.

In this demonstration, we will re-create the effects of a lava lamp using common household items, with no electricity needed! The “blobiness” effect will wear off during the demonstration, but you can regenerate it whenever you want!

The Experiment

Supplies: A clean 1-liter clear soda bottle, tap water, vegetable oil or baby oil, fizzing tablets (such as Alka Seltzer), and food coloring.

What to do: Pour the water into the bottle until it is about 1/3 full. Use a measuring cup or funnel to slowly pour oil into the bottle until it’s almost full. You may have to wait a few minutes for the oil and water to separate. Add about 10 drops of food coloring to the bottle (red is nice, but any color will look great.) The drops will pass through the oil and then mix with the water below. Break a seltzer tablet in pieces and drop a piece into the bottle. DO NOT PUT THE CAP ON THE BOTTLE. Observe what happens. Continue to add pieces of the seltzer tablet as you see fit. What happened inside the bottle after you added the seltzer tablet pieces?

What is happening: The oil floats on top of the water because it is less dense (see the liquid density experiment for more information). The fizzing tablet contains a mixture of powdered acids and bases that begin to combine as they dissolve in the water (see the carbon dioxide experiment). As the tablet dissolves, it creates carbon dioxide gas. As the gas rises through the oil, it takes some of the water with it. When the gas bubble reaches the surface of the oil, the bubble “pops,” allowing the gas to escape, and the water sinks back down through the oil to the bottom.

Extra: Once your tablet pieces are completely dissolved and the reaction is over, you can store the oil & water mixture with the cap on to save for later. To make more blobs, simply add more tablet pieces!

Links

To see this demonstration in action, head over to BASF’s YouTube page.