Leonie Boshoff-Mostert Edited by Anne Starace

Transcription

1 GASES, LIQUIDS AND SOLIDS: Condensation Leonie Boshoff-Mostert Edited by Anne Starace Abstract Matter is sorted into three groups: solids, liquids and gases. Solids, liquids and gases each have characteristic properties. This activity illustrates some of those properties. Keywords: molecule, condensation, physical change "Science is simply a way of looking at the world with an open, inquiring mind. It usually starts with an observation" Dr. David Darling Funded by the National Science Foundation and the University of Nebraska

2 Content Standards K History & Process Standards K Skills Used/Developed: 2

3 TABLE OF CONTENSE I. OBJECTIVES...4 II. SAFETY...4 III. LEVEL, TIME REQUIRED AND NUMBER OF PARTICIPANTS...4 IV. LIST OF MATRIALS...4 V. INTRODUCTION... 4 VI. PROCEDURE...6 VII. FREQUENTLY ASKED QUESTIONS... 7 VIII. REFERENCES

4 I. OBJECTIVES Students will: -learn the properties of solids, liquids, and gasses. -observe the effects of condensation of water. II. SAFETY Do not let participants come close to the hot plate. Make sure the can is completely cold before passing it around. III. LEVEL, TIME REQUIRED AND NUMBER OF PARTICIPANTS LEVEL This activity is suitable for grades k-6. TIME REQURED About 20 minutes NUMBER OF PARTICIPANTS About 3-15 IV. LIST OF MATERIALS pop can water hot plate tongs tray of cold water large enough to hold pop can V. INTRODUCTION Molecules Atoms are the building blocks for all matter. In nature most atoms do not exist alone. They combine with other atoms to form molecules. Molecules are very, very small and you can't see them with your naked eye - you need a very powerful microscope to see them. Solids, liquids and gases are the three different forms of matter. If something changes from one state of matter to the other, say from a liquid to a gas, it is still made of the same molecules. Changing states of matter is a physical change, not a chemical one. Everything and anything in the world is matter in one stage or another 1. As different as they are, the three forms of matter are the same in a few ways: 4

5 all matter occupies space all matter has mass all matter consists of tiny units called atoms Under normal conditions, most substances occur in just one of these states. For example, we think of iron as being a solid. But if it is heated enough, iron will turn in to a liquid, and eventually into a gas 2. What do we know about gases, liquids and solids? Then gases, liquids and solids will be explained intuitively, making use of posters and encouraging a lot of audience participation - i.e. asking them what they already know about gases, liquids and solids. Can we touch it? Feel it? What does it do? Does it flow? SOLIDS Solids have a definite size and shape. If you look at a solid through a powerful microscope you see that the molecules are packed tightly together. Though the individual molecules are shaking and vibrating, they are all fixed in one spot. The molecules of most (not all - think of an exception! wood) solids are carefully arranged in set patterns. Any material with its atoms and molecules in a definite pattern that is repeated throughout the material is called a crystal. layer C layer B layer A Figure 1 Crystalline Solid LIQUIDS Did you know? three quarters of the earth's surface is covered with liquid water over half of your body weight is water only two liquids, water and oil, are found in nature (But often these liquids have tiny particles in them that make them look different from pure water or oil. For example, blood is water with blood cells in it. ) If you could see the molecules in a liquid you would notice that they are packed together, but not as tightly as in a solid. And they are not in any particular pattern or order. They are randomly scattered around. One property of all liquids is that they flow. Although liquids take up a definite amount of space, they have no shape - liquids take the shape of the container they are in. Liquids always seek their own level. Think of water in a bowl, 5

6 no matter how you lean the bowl, the water does not tilt. Liquids always stay level because of gravity and because the molecules in liquids attract each other. Figure 2 Liquids always stay level GASES Gases are a form of matter in which the molecules are much farther apart than in either solids of liquids. The size of the gas molecules is tiny compared to the distances between them. Gas molecules move around constantly and therefore they spread and fill up any container. Like liquids, gases have no shape, but take on the shape of the container they are in. When a gas spreads out we say it diffuses. One way to test this is to go into a room and shut the door and windows. Then stand in one corner with a closed bottle of a smelly liquid, say vanilla essence. Have a friend stand in the opposite corner. Open the bottle and slowly wave it back and forth in the air to help the smell get out. See how long it takes for diffusion to carry the smell - which is vanilla essence gas molecules - across the room. Gases change size. If you have a balloon filled with Helium gas and you let the gas escape into a room it will diffuse through the room. The Helium gas changed from the size of the balloon to the size of the room - even though it is spread very thinly. The gas we know the best is air! VI. PROCEDURE SETUP Pour 15 ml of water into the empty pop can EXECUTION Heat the pop can filled with 15 ml of water it on the hot plate until a cloud of condensed water vapor escapes from the mouth of the can for about 20 s. Using the tongs, quickly lift the can from the burner and invert it in a tray containing cold water to a depth of a few centimeters. The can will collapse instantly. This activity shows 2 different forms of water: gas (water vapor) and liquid. When the can is cooled the water vapor "shrinks" to form a liquid - we say it condenses. The liquid water takes up much less volume than the gas did - so the can has to shrink! CLEANUP Turn off hotplate. Pour water down a sink. Recycle pop can. 6

7 VII. FREQUENTLY ASKED QUESTIONS VIII. REFERENCES 1. M Berger, "Solids, Liquids and Gases", G. P. Putnam's Sons, New York, D Darling, "From Glasses to Gases", Dillon Press, New York,