Water

Underwater Fireworks

by

Fireworks are fabulous! We love watching the colors explode and gently float down through the air, but we can’t watch fireworks all the time. Underwater fireworks are something we can watch any time, even in our kitchen!

The Experiment

Supplies: Water, vegetable oil, food coloring (any color), a large clear glass, a second smaller glass, a fork

What to do: Fill the large glass almost to the top with room-temperature water. Pour 2 tablespoons of oil into the other glass. Add 2 drops of food coloring to the glass with the oil. Vigorously stir the oil into the food coloring using a fork. Stop once you break the food coloring into little drops. Pour the oil and coloring mixture into the tall glass. Now watch! The food coloring will slowly sink in the glass, with each droplet expanding outwards as it falls.

What is happening: Food coloring dissolves in water, but not in oil. This has to do with the incompatibility of the molecular structures of the water and the oil. When you pour in the food coloring/oil mixture, the oil will float at the top of the water because it is less dense. The food coloring will begin to dissolve once it sinks through the oil and into the water.

Take It Further

Variations on this demonstration:

  • Try mixing in one drop each of two different food colorings.
  • What happens if you omit the oil and drop the food coloring directly into the water?
  • Try varying the size or shape of the water glass, the amount of the oil, or the amount of the food coloring. Just remember, when you are manipulating variables to only change one thing at a time!

Links

For a more detailed explanation of the miscibility of fluids, along with a more expansive version of this demonstration, head over to the Scientific American website.

Water That Coin

by

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

by

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.

Exploring Density

by

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

by

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.

Evaporate Some Water, Part 2

by

In the first Evaporate Some Water experiment, we explored the water cycle and how water can be converted into water vapor using only the energy from the sun. But what happens to water that is not in a stream, lake, or ocean?

The Experiement

Supplies: Two clear glasses of the same size, a marker pen, a piece of cardboard that will cover one of the glasses, tape, food coloring (optional).

What to do: Put a vertical strip of tape on the side of each glass. Measure out enough water to fill each glass about 3/4. Fill each glass with the exact same quantity of water. Add food coloring, if available. On the piece of tape, mark the water level on each glass. Tape the cardboard cover onto one of the glasses so that it does not fall off. Place both glasses in direct sunlight and leave them for a full day of sunlight. Then observe the level in each glass. Which glass had more water evaporated out of it?

What is happening: The piece of cardboard blocked the water vapor from reaching the atmosphere, so the water stayed inside the glass. Blocking the top of the glass created a miniature closed ecosystem, where the water evaporated into the space in the top of the glass, then condensed and returned to the pool of water below. The Earth is a closed ecosystem on a grand scale, with our atmosphere trapping the water and keeping it here, just like the cardboard kept the water in the glass.

Links

To find out more about closed ecosystems and instructions on how to make one of your own, visit NASA’s Climate Kids website!

Evaporate Some Water

by

Matter exists in one of four different categories or states – solid, liquid, gas, or plasma. Some molecules can exist in multiple states, while others will only ever be in one. When we think of water, we usually think of the liquid that comes out of our faucet, falls from the sky as rain, or fills creeks, rivers, ponds, lakes, and oceans. The water in these examples is in liquid form, but if you heat up water, it changes. It stops being a liquid and becomes a gas called water vapor. Another common name for this vapor is steam. Similarly, when liquid water gets really cold, it changes state again. This time it becomes a solid – ice.

The water that exists on the surface of the Earth is the same water that has been here for millions of years. On the surface of the planet, water can be found in liquid form (water), or as a solid (snow and ice). Water can also be found in the atmosphere as water vapor. Water moves from the atmosphere to the planet as precipitation. Water moving from the planet to the atmosphere is called evaporation. When there is more energy from the sun present, like on a hot, sunny day, water evaporates more quickly. Humidity refers to the amount of water vapor in the air. High humidity is when a large amount of water vapor is present. Low humidity is when little water vapor is present.

The Experiment

Supplies: A hot sunny day, chalk, a paper cup of water, a flat portion of concrete, a watch or clock.

What to do: Pour some water on the concrete or asphalt to make a puddle about 18 inches in diameter – preferably in full sunlight. Use the chalk to make a circle around the edge of the puddle. Every 15 minutes or so come back to examine the puddle and draw a new circle around it.
What happened to the puddle each time you checked on it? How long did it take for the puddle to disappear entirely?

What is happening: Energy from the sun, in the form of heat, changes the water from liquid to water vapor, causing it to evaporate into the atmosphere.

Links

To learn more about evaporation and the water cycle, head over to the National Geographic Kids website.

Work With Ice Power

by

Everything in the universe is made of matter, but not all matter is the same. Matter can be sorted into one of four different categories – solid, liquid, gas, or plasma. Some molecules will only ever be found in one of the four states, while other molecules can shift from one state to another, depending upon the conditions surrounding that molecule.

One of the things that can make a molecule shift from one state to another is temperature. When we think of water, we usually think of the liquid that comes out of our faucet, falls from the sky as rain, or fills creeks, rivers, ponds, lakes, and oceans. The water in these examples is in liquid form, but if you heat up water, it changes. It stops being a liquid and becomes a gas called water vapor. Another common name for this vapor is steam. Similarly, when liquid water gets really cold, it changes state again. This time it becomes a solid – ice.

Different states of matter are organized differently at the atomic level, as demonstrated in the picture. The more energy that molecules are exposed to the more “excited” they become, and they start to move around more. Exposing water to increasing or decreasing amounts of energy, in the form of heat, causes the water to change its state. Molecules may need a different amount of space, depending upon what state they are in.

The Experiment

Supplies: A freezer-safe container with a lid, water

What to do: Fill the container with as much water as you can while still being able to carry it without spilling! Set the container in the freezer where it won’t be disturbed for several hours. Now, add more water, until the container is filled all the way to the brim. Set the lid loosely on the top. DO NOT TIGHTEN THE LID. After several hours, come back to check on your container. What happened to the water? What happened to the lid?

What is happening: As with the water/rubbing alcohol experiment, when water is in its liquid form, the molecules can squish together more easily. In its solid form (ice) the water molecules take up more space, so the water will expand in volume as it freezes. For a variation of this experiment, pour 1/2 cup of water into a liquid measuring cup. Make sure the water is to the line. Freeze your measuring cup and water for several hours. Where on the measuring cup is the surface of your ice?

Links

For more information on states of matter, check out the Chem4Kids website.

Find the Invisible Space

by

Matter is what scientists call all the stuff around us. Matter may come in all different colors, shapes, and sizes, but all matter can be “broken down” into smaller parts – all the way to the atomic level. At its core, matter is just a bunch of different atoms that have gotten together in an organized fashion. Atoms are the core building blocks of everything around us.

Atoms are super tiny, so small that they can only be seen with a special kind of microscope. Atoms have a center, called a nucleus, which contains parts called protons and neutrons, and they have things called electrons that float around the outside of the nucleus, sort of like how the moon “floats” around the Earth. Every atom has some “invisible space” that exists between the nucleus and the electrons.

Think of a bin filled with loose LEGO. Each individual piece represents an atom. When you put two or more atoms together, you create a molecule. Different molecules have different shapes and sizes. When you put multiple molecules together, you get a compound. Compounds can be combined to make anything, just like LEGO bricks, but regardless of what you build, the invisible space still exists at the atomic level.

Even though we can’t see the invisible space, we can still prove that it exists using everyday objects.

The Experiment

Supplies: A 1 cup measuring cup, a measuring cup that is at least 2 cups, water, and rubbing alcohol.

What to do: Measure EXACTLY 1 cup of water very carefully and pour it into the large measuring cup. Measure EXACTLY 1 cup of rubbing alcohol and pour the rubbing alcohol into the large measuring cup. Check the amount of liquid in your large measuring cup. Is it 2 cups of liquid?

What is happening: Water molecules consist of a single oxygen atom combined with two hydrogen atoms. Rubbing alcohol molecules have three carbon atoms, seven hydrogen atoms, and a single oxygen atom. The shape of the rubbing alcohol molecules allows them to “slide” in-between the water molecules and fill the invisible spaces. This is one case where 1 + 1 does NOT equal 2!

Links

To learn more about atoms, check out Rader’s Chem4Kids website.