Chapter 2
Condensation and Freezing
Clouds gather on a stormy day, dew catches on a spider web, snowflakes fall, and ice cracks. Water takes on many forms in the world around us. It turns to vapor and forms droplets that make the clouds that rain down and moisturize the earth. And water freezes and turns to snow and ice. How does this happen?
TRY THIS
SWEATY SODAS!
If you hold a cold glass of water on a hot day, the glass gets sweaty. That moisture is called condensation.
QUESTION
What causes condensation?
WHAT YOU NEED
2 plastic cups
Water
Ice
Towel
Stopwatch
WHAT TO DO
FUN FACT
Icy Breath
Did you know you can see water vapor? On a cold day, when you breathe out, you can see a white cloud. That cloud is condensed water vapor.
WHAT'S HAPPENING
The outside of the cup with water is dry. But the outside of the cup with ice and water is wet. Congratulations, you've just made dew! If you've ever walked around in the wet grass on a cool summer morning, you've felt dew. The next time you take a hot bath or shower, look at the mirror when you get out of the tub. Why is it all fogged up?
The air around us is saturated, which means it is full of water vapor. Water vapor is the gas state of water. When you added ice to the second cup, the cup became cool. The cup then cooled the air around it. Cool air can't hold as much water vapor as warm air, so the water vapor becomes droplets of liquid. The drops attach to the cup. These drops are called dew. In the case of the mirror, the tiny drops of water from the steamy bath are clinging to the cold glass of the mirror. Draw a smiley face!
Later in this book you'll learn about meteorologists — people who study the weather. They use the dew point to tell the humidity of the air. Airline pilots also rely on dew point to fly safely in icy or foggy conditions.
YOUR NOTES
Try this experiment using fewer ice cubes. Is the outside of the cup less wet? Add more ice cubes and see what happens.
What if you use different kinds of containers, such as metal or glass?
Try this experiment in the bathroom after a hot steamy shower. What happens?
WORD to KNOW
condensation: the process by which water changes from a gas to a liquid.
water vapor: water in the form of a gas, present in the atmosphere.
Do the experiment again, but put a thermometer in the cup with the ice. When you see dew appear, look at the temperature on the thermometer. This is the dew point temperature.
Record the time it takes dew to appear on the following lines.
Fewer ice cubes 
More ice cubes
Metal container
Glass container
Steamy room
Dew point temperature
FUN FACT
Control Yourself!
When scientists do experiments, they keep one part of the experiment unchanged. You did this when you filled one plastic cup with only water. This way you know that the change in the second cup happened because you added ice. The part that stays the same is called the control.
TRY THIS
JACK FROST'S SECRET
Have you ever seen icy patterns on your windows in the dead of winter? Where did they come from?
QUESTION
What causes frost?
WHAT YOU NEED
2 plastic cups
¼-cup measure
Rock salt (you can use the kind that's meant for making ice cream)
Ice
Water
Towel
WHAT TO DO
WORD to KNOW
frost: the layer of tiny ice crystals on a cold surface.
WHAT'S HAPPENING
As you can see, a thin layer of white ice has formed on the outside of the cup with the rock salt. This is frost.
When you made dew in the last experiment, the water vapor cooled from a gas to a liquid. The rock salt in this experiment allowed the temperature of the water in the cup to get even colder, dipping below the dew point temperature. So now instead of drops of liquid on the outside of the glass with rock salt, you have ice crystals, or frost.
Outdoors, frost can cause problems. Car windows become coated in a hard white layer that's difficult to remove and impossible to see through. Flowers and fruits in gardens freeze, ending their growth period. But in the mountains, a special kind of ice crystals called hoar frost can cause a very big problem. If hoar frost forms on top of a layer of snow, and then the frost is covered by a new layer of snow, this can cause an avalanche. It's important to know what the weather is like when you go out in winter so you can be safe.
YOUR NOTES
You can test frost the same way you tested dew in the last experiment. Try different containers. Put the glass in the freezer. Does the frost appear more quickly? At what temperature does the frost appear? On the following lines, record the time it takes frost to appear.
Metal container
Glass container
Freezer
Frost point temperature
Cool Quotes
Science does not know its debt to imagination.
— Ralph Waldo Emerson
Air-mazing
Air reacts with natural chemicals in some kinds of fruit. The result of this chemical reaction is very easy to see! Break the Upside-Down-Flip-Flop code for directions to do a colorful experiment that shows this reaction.
From the Piggy Bank
You can brew up a nice batch of copper acetate using a simple chemical reaction. To find directions on how to do this, you must choose between the two sets of different letters in the puzzle grid. Use a light-colored marker to highlight the set of letters you want, then read them from left to right, top to bottom.
YUM-istry
Chemists work closely with candy makers to come up with the formulas for some of our favorite treats. Their job is to make sure each candy behaves the way it is supposed to.
Which candy is described on this page? Cross out the box marked with a dot. Continue clockwise around the border crossing out every other box. Read the descriptions that remain.
SCIENCE LAB: SLIPPING, SLIDING AWAY!
Be careful walking outside in winter — there's often ice on the sidewalks. Walk slowly, make sure you can keep your balance, and then try sliding slowly along the ice. The slippery surface of ice allows you to slide over something that isn't usually slippery, like cement. But ice is dangerous and you can fall and hurt yourself. So towns usually try to keep their citizens safe by placing salt or sand on top of the ice to provide traction.
QUESTION
Which substance makes an icy surface less slippery: salt or sand?
WHAT YOU NEED
3 ice cubes
3 small plates
½-teaspoon measure
Salt
Sand
Stopwatch
WHAT TO DO
WHAT'S HAPPENING
As you discovered in the frost experiment, salt allows water to remain liquid at a lower temperature. So salt is the best way to melt icy sidewalks. But sand provides traction, which means your finger doesn't slide easily across the sandy cube. So if you want to walk safely across a slippery sidewalk, sand is the best thing to use. Also, the kind of salt that is used to melt ice outdoors is not good for the environment. So some cities are now using sand on wintry roads and sidewalks.
YOUR NOTES
Does your family use salt or sand outdoors in the winter? Try using sand instead of salt and see if you can walk more easily on the ice. Always walk carefully and hold an adult's hand if you think you might fall.
Carbon Dioxide
Take a deep breath. Now let it out. You've just exhaled carbon dioxide, a gas that is used for so many things in our world. The chemical symbol for carbon dioxide is CO2, because it contains both carbon (C) and oxygen (O). Plants use CO2 to make food during photosynthesis — a process that gives off oxygen, which animals breathe in to live and have energy. Carbon dioxide is released in small amounts by volcanoes when they erupt, and it is used to make bubbly beverages. Normally you can't see carbon dioxide, but you can see its effects in the following experiments.
WORD to KNOW
carbon dioxide: a colorless, odorless gas that is found in carbonated sodas.
FUN FACT
Raisin' a Raisin
Do you know how raisins are made? At the end of the summer, grapes are set out to dry in the sun. After a few weeks, the sundried grapes have turned into raisins.
What did one raisin say to the other raisin at the gym?
You're in “grape” shape!
TRY THIS
RAISIN BEBOP
Cola, ginger ale, seltzer water — these are all fun drinks because they're full of bubbles that tickle your throat when you drink them. And they can make you burp! But these drinks are fun in other ways, too!
QUESTION
What makes raisins dance in a glass of fizzy water?
WHAT YOU NEED
Can of clear soda — seltzer water or a lemon-lime soda works well
Tall see-through glass
Handful of raisins
WHAT TO DO
WHAT'S HAPPENING
Soda water has more than just water in it. It has CO2, a gas that creates the bubbles you see in the soda. When you dropped the raisins into the glass, they sank to the bottom and became coated in bubbles. This is because the surface of a raisin has little pockets. Those pockets trap bubbles of air that grab some of the carbon dioxide in the soda. The bubbles cause the raisins to rise to the top of the glass. Once the raisins reach the top of the glass, the bubbles pop, the carbon dioxide is released, and the raisins sink back to the bottom. The bubbles act like a life jacket, making the raisins more buoyant, which allows them to float and sink. If your raisins aren't sinking, give them a little tap to knock off the bubbles.
YOUR NOTES
Draw a picture of your be-bopping raisins.
What other foods could you use in this experiment? How about uncooked pasta or lemon seeds? What happens?
Way to Glow!
Mix together oxalate ester and fluorescent dye, add some hydrogen peroxide and shake. Something really amazing happens! What? You don't know what these chemicals are? Maybe not, but you have probably done this experiment more than once! Break the Letter Shift code to learn when that was.
TRY THIS
DISSOLVING CHALK
You can draw all kinds of cool pictures with sidewalk chalk using different colors and sizes. Eventually the chalk sticks wear down as you use them. But did you know you can dissolve, or erode, chalk using a liquid?
QUESTION
How does a liquid dissolve a piece of chalk?
WHAT YOU NEED
Bowl
Vinegar (white or cider)
Blackboard chalk
Stopwatch
WHAT TO DO
WHAT'S HAPPENING
Chalk is made up of limestone, or calcium carbonate. The vinegar is made up of an acid called acetic acid. The acid eats away at the calcium carbonate, releasing bubbles of carbon dioxide. That is why you see bubbles forming around the chalk.
FUN FACT
Limestone Caves
There are many caves that have been formed by carbonic acid dripping onto limestone over thousands of years. The acid slowly eats away at the stone, carving out the space for a cave. Limestone is made up of tiny pieces of sea shells and a mineral called calcite.
WORD to KNOW
limestone: rock formed mostly by remains of sea shells and consisting of calcium carbonate.
FUN FACT
Giant Cave
Sarawak Chamber, in Malaysia, is the largest cave in the world. It is 2,300 feet long, 980 feet wide, and more than 230 feet high. When cavers discovered it, they couldn't see the end of their flashlight beam because the cave was so enormous!
In nature, carbon dioxide gas is always present in the air. And this gas can get into our rain, turning it slightly acidic. Usually this is not a problem, and this naturally acidic rain has helped shape many of the mountains and canyons in our landscape. However, now there's too much carbon dioxide in the atmosphere from our cars and our factories. And the rain has become too acidic, damaging forests and eroding our mountains.
YOUR NOTES
How long did it take for the chalk to start dissolving?
Which Is Which?
Take three glasses of water. Add a few drops of vanilla to one glass, a drop of perfume to the next glass, and several drops of onion juice to the last. Look away and have a helper switch the glasses around. Can you think of an easy chemical reaction that will help you to tell which glass is which?
SCIENCE LAB: BURPING BALLOON
Some caves are deep underground, and they don't have much oxygen. However, they do have a lot of carbon dioxide. But you don't know how much because CO2 has no smell. There is a simple test you can do, and it's similar to the following experiment.
QUESTION
What gas can put out a flame?
WHAT YOU NEED
Adult
Measuring cup
Vinegar
Small bottle
Funnel
Balloon
Teaspoon
Baking soda
Clay
Wide jar
Small candle
Matches
WHAT TO DO
WHAT'S HAPPENING
Mixing baking soda and vinegar causes a chemical reaction that creates carbon dioxide gas. Unlike oxygen, which makes a flame burn faster, and hydrogen, which also burns, carbon dioxide is used to put out fires. So when you released the balloon full of carbon dioxide, the candle flame went out.
It's important to always practice fire safety. Not all fires can be put out with just water. Make sure your kitchen has a fire extinguisher. It uses carbon dioxide to put out a fire.
In a deep underground cave, explorers called cavers will carry a butane lighter with them. If they are starting to have trouble breathing, they flick open the lighter and look at the flame. If the flame immediately goes out or doesn't appear at all, then they head straight back to the entrance. There is not enough oxygen in the cave for them to safely explore.
YOUR NOTES
Draw a picture of your experiment and label each part. You are making a diagram. You can use this drawing to recreate the experiment.
What other acidic liquids could you use? Try lemon juice, orange juice, or grapefruit juice.
Chemical Changes
Chemical changes happen in the world around us every day. When you boil a raw egg, you cook it and change its form. When food goes bad or a candle burns or a metal rusts, a chemical change has occurred. In a chemical change, you have a new product that you didn't have before. Perhaps now you have a new gas, a new odor, or sound, or heat. In the following experiments you'll see some pretty amazing chemical changes.
TRY THIS
OOBLECK
What's white and goopy and hard and drippy at the same time? Stumped? Do this experiment and you'll find out!
QUESTION
Can you create a substance that is both a liquid and a solid?
WHAT YOU NEED
Large bowl
1-cup measure
½-cup measure
Water
Cornstarch
Spoon
Paper towels
Food coloring
WHAT TO DO
WORD to KNOW
chemical change: a chemical process by which a new substance is created.
FUN FACT
Seuss Science
Oobleck is named for some very odd stuff that falls out of the sky in a book called Bartholomew and the Oobleck by Dr. Seuss.
WHAT'S HAPPENING
Matter, what things are made of, has four states: solid, liquid, gas, and plasma. In this experiment, you combined cornstarch, a solid, with water, a liquid. The cornstarch and water created a chemical change, resulting in a unique mixture that acts like a solid when it has pressure on it and acts like a liquid when it has no pressure. When you tapped the oobleck, it felt hard because you were putting pressure on it. When you grabbed it and then let go, the oobleck oozed out of your hand because you had released the pressure. You have made a substance that exists in two states of matter.
YOUR NOTES
Try putting the oobleck into a plastic container and hitting it against a table. What happens?
Try making a ball out of the oobleck. When you let go of the ball, what happens?
Try picking it up with a spoon or a slotted spatula. What happens?
TRY THIS
SPY SCHOOL
Ready for a top-secret assignment? In this experiment you're going to learn how a popular form of secret message is created so you can make your own. What will you write using your homemade invisible ink?
QUESTION
What makes invisible ink visible?
WHAT YOU NEED
Lemon juice
Cup
Paintbrush
Paper
Friend
Hot lamp
WHAT TO DO
Why did the spy send a secret message using lemon juice?
Because he thought it would be a-peel-ing!
Tasty
A chemist has a pile of tasty and nice smelling leaves. She wants to use the flavor and aroma but keep the dry and woody parts of the leaves separate. Connect the dots to find out one way she can do this!
WHAT'S HAPPENING
When you applied the lemon juice to the paper, you could probably see your writing at first, but then the juice dried and your writing disappeared. Presto! Your message was hidden.
To make your message appear, you held the paper close to the lamp. The heat in the lamp caused a chemical change — the water molecules in the lemon juice evaporated from the heat, leaving behind sugar molecules. The sugar molecules reacted to the oxygen in the air and turned brown, revealing the secret note.
Secret messages can be made and revealed using all kinds of methods. Ultraviolet light, for instance, is used by the United States Postal Service to print routing information on packages. The information is not visible without an ultraviolet light.
Sometimes, even though a message is “invisible,” it is still possible to tell that a blank piece of paper isn't really blank. If you look carefully, you might just see the juice sitting on top of the paper.
YOUR NOTES
Try this experiment with other citric acids, such as orange juice and grapefruit juice. Do they work as well as the lemon juice did?
SCIENCE LAB: STOVETOP PLASTIC
Quite a few of the things we use every day are made of plastic. And they are usually made in a factory using chemicals. But hiding in your fridge and cabinets are two ingredients that, when put together, make a simple kind of plastic that can be molded and decorated.
QUESTION
How do you make plastic?
WHAT YOU NEED
Pint of milk
Adult
Saucepan
Mixing spoon
1-teaspoon measure
White vinegar
Sieve
Large pan
Rubber gloves
Water
WHAT TO DO
WHAT'S HAPPENING
Milk contains a protein called casein. This protein is not something you can taste in regular milk. But when you add an acid, such as vinegar, and heat, the protein turns into lumps. These lumps are similar to the plastic used in almost everything we own. This chemical change is a big one — don't eat the lumps, they're not made of milk anymore and it's not safe!
YOUR NOTES
Describe the smell and feel of the plastic you just made.
What did you make with your plastic? Draw a picture of it here.
WORDS to KNOW
protein: an essential part of the food we eat that helps our bodies grow healthy and strong.
WORD to KNOW
Yummy Cheese
An Indian cheese called paneer is made by adding lemon juice to milk. But the cheese curds are soft and edible, unlike the plastic you made.