Matter

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.

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!

Evaporate Some Water, Part 2

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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

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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

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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

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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.