Play Quizlet. Just scroll down and click on Physical, then scroll to find the Module you want.
Hydrosphere - hydro means water; sphere is... well, a sphere! =) The earth is sometimes called the blue planet, since from outer space, all the water makes it appear blue. Over 70% of the earth's surface is covered in water, not counting what isn't seen. Over 97% percent of the earth's water is ocean water and isn't drinkable. Less than 3% is freshwater, and most of that is in the glaciers and icebergs. A large percentage of what is left of our freshwater is underground!
So how do we get drinkable fresh water?
The hydrologic cycle is the way the water is continuously exchanged between earth's various water sources - oceans, lakes, ponds, rivers, creeks, and streams.
The main ways water gets into the atmosphere is by evaporation and transpiration. Transpiration is emission of water vapor from plants. When these take place, water vapor goes into the atmosphere forming clouds. This is condensation. This falls from the atmosphere to the earth in a form of precipitation.
The kids mixed ¼ cup of salt into a pot of water, then heated it on the stove to speed up the process of evaporation. They took turns holding a lid partially over the pot, with the other part of the lid over a bowl. A bag of ice was placed on the half of the lid that was over the boiling water. This coolness caused the water vapor to turn back to a liquid, just like it does on the outside of a glass of iced tea. It is condensation of water vapor from the air.
As the water collected on the underside of the lid, it ran down the lid and dripped into the bowl. When they tasted the water in the bowl, it was fresh, not salty.
Water evaporates; salt does not. Remember in the last module, Experiment 4.3 showed that water can dissolve salt, but we learned the salt is still present in the water; you just can't see it. When water evaporates, the salt is left behind.
I emailed Dr. Wile and asked about this.
He answered, "Salt doesn't evaporate from the ocean because there isn't enough energy to allow that to happen. In order to evaporate, a given molecule needs a certain amount of energy. The energy needed for water to evaporate is available at room temperature. However, since the ions in salt are so strongly attracted to each other, it takes a LOT more energy to evaporate salt. That energy begins to be available at about 800 degrees Celsius. Thus, salt cannot evaporate at the temperatures the ocean experiences near its surface."
This is a form of distillation. A chemist uses this technique to separate a mixture of two or more substances. Each substance will evaporate at different temperatures, allowing him to separate them.
Oh, and cousin A made that potholder. Didn't she do a great job! =)
Experiment 5.2, Ice and Salt
The average salinity of ocean water is about 35 grams per 1,000 grams. This varies, since where the rivers flow into the ocean, the salinity is diluted. In other places, the salinity may be much higher.
As surface runoff passes over the rocks and soil, it dissolves the salt there, bringing it along with the water to the rivers, streams, etc, and eventually to the ocean. Rivers and streams do have a little salt! They are considered freshwater because there is so little, you can't taste it. Rivers are freshwater because of the limited time the molecules of water actually spend there. They continue on to the ocean, taking the salt with them. When the water reaches the ocean, it stays until it is evaporated, leaving the salt behind.
Freshwater lakes have rivers or streams running through them.
Can you imagine IF the earth was billions of years old? The ocean would be FULL of salt!!!
Later I finished the experiment. I took the partially frozen saltwater out of the freezer, and rinsed off any salt clinging to the ice. I put the remaining ice in a glass and let it melt. Rebekah tasted it and it was still salty!
Why didn't the freshwater freeze and leave the salt?
Remember the motion of molecules and atoms. For a liquid to freeze, enough energy must be removed to slow down the molecules. So the water molecules and dissolved salt must be slowed down. Therefore they freeze together. It takes a lower temperature, but they still freeze together.
They do not, however, freeze as saltwater. They separate out as they freeze, making solid water and solid salt. When the ice melts, the salt re-dissolves, making saltwater again.
These first three pictures of an ice cube with salt will show you that salt melts ice, which shows that saltwater freezes at a slower rate and at a lower temperature than freshwater.
I even let the 2 cups of saltwater freeze until the next day, and was able to break it apart by hand!
Your freezer might be colder than mine!
Since icebergs are composed of freshwater, this experiment disproves a myth that icebergs are a result of ocean water freezing. In certain polar regions, the water can freeze to form sea ice, but sea ice is not freshwater.
Icebergs come from mountains. Every iceberg starts as a glacier. The upper part of many mountains keep snow year round, and more is added each year. The accumulated weight presses the snow at the bottom into a thick, hard-packed layer. When it gets too heavy, it starts to slowly slide down the mountain. The average is about 1 meter a day. Partway down, it begins to melt a little, and feeds other freshwater sources. Glaciers in the polar regions never reach that stage, and stay frozen. Large chunks may break away and become icebergs. Greenland is nearly covered in a huge sheet of ice that comes from two glaciers!
Experiment 5.3, Cloud Formation
Once water has entered the atmosphere through evaporation or transpiration, it can either exist as a water vapor, making humidity, or it can condense and form clouds.This experiment shows how clouds form.
The kids added warm water to 2-liter bottles, about one-eighth full. They put on the lid, and squeezed the bottle, but nothing happened.
Then they lit a match, let it burn for a minute, and dropped it into the water where it extinguished. After quickly capping the lid, they squeezed the bottle and released it. Instantly the sides of the bottle were foggy. They had made a cloud! Vapor attaches to tiny smoke particles, just as vapor attaches to particles in the atmosphere to form clouds. Each time they squeezed the bottle again, however, the "fog" disappeared, and returned once they let go. When the bottle was squeezed, the air was put under pressure, containing it in a small volume. When released, the air expanded back to it's original size. When heated, liquids usually expand and become a gas because the liquid was given energy. But adiabatic cooling is cooling (not heating) of a gas when that gas expands. The gas was given no energy to make it heat. The cooling caused some of the water vapor in the bottle to condense on the smoke particles. This made the cloud. =)
When air expands, and everything else stays the same, the gas will cool, causing condensation.
Most of us already know that if heated, air expands. Like the balloon in Experiment 3.2.
If a container of gas was released in a room, the gas would expand without being heated.
The first time the kids tried the bottle experiment, there was nothing for the water vapor to condense on. After adding the match, there were smoke particles for the vapor to condense on. Most clouds are water vapor formed around small particles in the atmosphere.
They kept playing with the bottles and used up a lot of matches! They have a lot of fun here every week. =)
Here's a video that does it a little differently.
This post got kinda long! Can you tell I love this science!?! =D
We loved the clouds in a bottle experiment. Isn't this class fun?
ReplyDeleteYes! I love it! =D
ReplyDelete