Science Wednesday - Friday September 21st - 23rd EQ: How is water important? What gives water its unique properties? On your desk: Paper Pencil for notes Assignments: Thirsty Abe Climbing Water Water Metal Heat Comparison Everything else in the floor 1
How do we use water? 1. Agriculture - Irrigation. Parts of the country that are the least suitable to grow crops are productive farm land because of irrigation. The irrigation of Chinese rice paddies dates back to 3000 BC. Irrigation is moving water for plants from one area to another area that does not have water. 2. Industry - Nearly everything that is manufactured or made requires water to be used in mixing ingredients, during the manufacturing process, or to cool machinery. 3. Transportation - Since ancient times, mankind had used the ocean, rivers, lakes, and streams to move goods from one area to another. Transportation on water is relatively cheap, and easily developed. 4. Recreation - We also use water to swim, play, ice skate or boat. WATER IS ESSENTIAL FOR LIVING THING TO GROW, REPRODUCE, AND CARRY OUT OTHER IMPORTANT PROCESSES SUCH AS PHOTOSYNTHESIS. WATER MAY ALSO BE AN IMPORTANT PART OF AN ANIMAL'S HABITAT. 2
3
Oceans - Even though the oceans have been named, those names represent regions. It is truly 1 large interconnected ocean. Ice - The largest source of fresh water is in ice. These are the polar ice caps, permafrost, and icebergs. Rivers and Lakes - The Great Lakes cover and area that is nearly twice the size of New York state. The Great Lakes also contain almost 20% of ALL the water in the world's freshwater lakes. These are considered surface water because they can be touched. Ground Water - The largest useable source of freshwater. This water trickles down through spaces between the particles of soil and rock. It eventually reaches a layer that it cannot pass through or soak into. It fills the spaces and stays underground until we pump it to the surface. 4
Over the past few days we have gotten to observe and see how water behaves when compared to other liquids, and when compared to metals. We saw that water did some pretty unique things. The question then becomes, how does water do that? Like all matter, water is made up of atoms. Atoms are the smallest building block, or unit of matter that you can have. There are 118 known elements. The smallest piece of that element is called an atom. Atoms, will attach to form bonds. Just like the 26 letters of the alphabet, there are many different compounds that these atoms can form. Below is a water molecule. (molecule is the smallest piece of a substance that you can have and still have that substance.) It is made up of 2 Hydrogen atoms and 1 Oxygen atom. We write the chemical name for water as H 2 O. 5
+ + Because of the structure of this molecule, water tends to have a positive end of the molecule and a negative end of the molecule. The positive charge comes from the hydrogen atoms and the negative comes from the oxygen end of the atom. Because of this charge effect over the molecule, water is a polar molecule. Because water consists of polar molecule, it is said to be a polar substance. The polarity of the molecule acts much like two magnets that attract one another and will repel one other if the same poles are lined up. The positive end of the water molecule is attracted to the negative end of another water molecule. Positive end to positive end or negative to negative will repel each other. 6
+ H O + + ++ + + + H Electron Proton + The reason that water has polarity is due to the way that the oxygen and the hydrogen share electrons. They form a bond in which the hydrogen electrons travel around the oxygen atom. This means there are more protons on the hydrogen end of the atom. (Protons are +; Electrons are -!) That gives the oxygen atom two more electrons, or negative charges, than protons. That is why the oxygen end of the molecule tends to carry a negative charge. Because the hydrogen is sharing its electrons with oxygen, the hydrogen atoms will tend to have a positive charge, because it has extra protons, or positive charges. 7
This polarity, gives water some very unique properties and characteristics. Surface Tension: Surface Tension is what allowed the water to "bubble up" on the head of a the coin or token. The molecules will pull together tightly and will hold together. The attraction of the molecules makes for fairly strong bond. The molecules on the surface not only hold to one another, but also hold on to the molecules under the surface. Surface tension is what allows a bug to walk across the surface of the water without falling in. Surface tension is also what makes water form a drop on the windshield of a car. http://dsc.discovery.com/videos/timewarpwaterdroplet.html 8
Capillary Action: When we look at water in a cup or straw, the water appears to be climbing the side of the straw. Water will also climb the pores of brick or wood. Just as the molecules want to stick to each other (cohesion), they also want to stick to the other objects (adhesion), such as wood, paper towel... As the molecules stick to another object, they will pull other molecules along with them. The combined forces of cohesion and adhesion, allows water to move through materials with pores or narrow spaces. This property of water is the foundation for moisture wicking clothes that keep you cool. 9
Universal Solvent: Solution is a mixture that forms when one substance dissolves another. Solvent - the substance that does the dissolving. Solute - the substance that gets dissolved. If we take a block of sugar and place it in a glass of warm water, the sugar (solute) will dissolve completely in the water (solvent). The sugar is a polar molecule as well as the water. Because they are both polar molecules, they are attracted to one another. Tiny molecules of sugar will attach to a water molecule. So they bond. Sugar with water, water with sugar. We can't see the sugar, but we can taste it. Water is said to be a universal solvent because so many things can dissolve in water; sugar, salt, soap, bleach, alcohol, oxygen, carbon dioxide. Because oil is not a polar molecule, has no charge, it will not dissolve in water. 10
Phases of Water: Gas: Liquid: Solid: Condensation Melt Evaporation Freeze Sublimation Notice that in the solid phase, ice, the water molecules have a crystalline structure. This structure is what allows ice to float. In the layout, the molecules take up more space than in the liquid form. Therefore the density of the solid water, ice, is less than the density of the liquid form. This is why ICE FLOATS! 11
One last important property or characteristic of water is Specific Heat: It is a hot day... You walk along the board walk to the beach and your feet are very hot. You walk along the beach and the sand burns your feet... you run toward the ocean, drop your stuff next your chair, and make it to the surf. SOOOOO thankful that the ocean can cool your feet... HUM??????? Why is the board walk hot, why is the sand hot, and why does the ocean cool my feet? They have all been sitting out in the sunlight for the same amount of time... HUM??????? All material has a property called specific heat. Specific heat is the amount of heat needed to raise the temperature of a certain mass of a substance by 1 o C. The boardwalk, and the sand do not need a lot of heat to get hot, much like a frying pan on the stove. They have very LOW specific heat... They will cool off quicker also! The water, ocean, has a very HIGH specific 12
Complete the Water Property Study Guide today in class. 16. Draw a water molecule and label the parts and the charges. Test Wednesday on this material. Review Vocabulary from last test! It could be on this test also! Quiz each other on the vocabulary terms from each section! 13