Properties of Water

1. Properties of Water

2. Water and Living Things • What do you and an apple have in common? You both mostly consist of water! In fact water makes up nearly 2/3 of your body.

3. The Water Planet Oceans cover nearly 71% of the Earth’s surface. Most (more than 97%) of the Earth’s water is salt. Only 3% is freshwater

4. 3% Freshwater About 2/3 of the freshwater available is found in Glaciers

5. 3% Freshwater Another fraction is found in the atmosphere as water vapor (the gaseous form of water). Less than 1% of Earth’s water is available for human use

6. Water’s Unique Structure • Water is made up of atoms, which attach together, or bond, to form molecules. • 2 hydrogen atoms bonded to an oxygen atom form a water molecule.

7. H2O Each end of the molecule has an electric charge. A molecule that has electrically charged areas is called a polar molecule. The positive hydrogen ends of one water molecule attracts to the negative end of another nearby water molecule. As a result they stick together.

8. CHECKPOINT Describe the arrangement of the atoms in a water molecule. What makes it a polar molecule?

9. Surface Tension Surface tension is the tightness across the surface of the water caused by the polar molecules pulling on each other. The water forms a curved shape. Surface tension also causes raindrops to form round beads when they fall onto a windshield.

10. Capillary Action How does water move up against the force of gravity? Just as water molecules stick to each other, they stick to the sides of objects. As they stick to the object, they pull other water molecules up with them. This is how water is able to move up the stems of plants. The combined force of attraction among water molecules and with the molecules of surrounding materials is called capillary action. Another example of capillary action is water climbing up a paper towel.

11. Universal Solvent • A solution is a mixture that forms when one substance dissolves another. • The substance that does the dissolving is called the solvent. • One reason that water is able to dissolve many substances is that it is polar. The charged ends of the water molecule attract the molecules of the other polar substances.

12. Universal Solvent • Water dissolves many substances and even gases, including oxygen and carbon dioxide. These dissolved gasses are important for organisms that live in the water. • Some substances do not dissolve, like oil and wax. • The molecules of oil are nonpolar molecules – they have no charged regions. Nonpolar molecules do not dissolve in water

13. CHECKPOINT List a solid, liquid, and a gas that dissolve in water.

14. Changing State • States, or forms include a solid, liquid or gas • The ice is solid, the water is liquid, and the water vapor in the air is a gas. • Water is the only substance on Earth that commonly exists in all of its different states. • Most other substances require extreme hot or cold to change states, for example a steel car door doesn’t melt on the hottest day in July. A piece of steel would remain solid even in your kitchen oven.

15. Melting • Think about an ice cube. The ice is solid; it has a shape because its molecules are arranged in a ridged structure. The ice is very cold. • Temperature is a measurement of the average speed of molecules. At -10 degrees Celsius the molecules are moving back and forth, but are not moving fast enough to break free from the structure. • If you put the ice in a pan on the stove, the heat energy will allow the molecules to move faster. The temperature reaches 0 degrees Celsius and the ice melts becoming liquid water.

16. Boiling and Evaporation • Liquid water takes the shape of the container it is in. This is so because the molecules move more freely, bouncing off each other. • If you boil water, the temperature increases and the molecules speed up. • At 100 degrees Celsius the water boils and a state change occurs. The molecules have enough energy to escape the liquid and become invisible water vapor. • Evaporation is the process by which molecules at the surface of a liquid absorb enough energy to change to the gaseous state

17. Condensation • As water vapor cools down, it releases energy to its surroundings. The molecules slow down and the temperature decreases. The temperature of the gas reaches boiling point, the vapor changes back to the liquid state. • The process by which gas changes to a liquid is called condensation.

18. Freezing • If the liquid continues to be cooled, the molecules lose energy and slow down. At 0 degrees Celsius the liquid water freezes, changing back into its solid state.

19. CHECKPOINT In which state do water molecules have the most energy?

20. Why ice Floats • Ice cubes float when you put them in glass of water. When water freezes the molecules line up forming grid like crystals, taking up more space than when in the liquid state. • Ice is less dense than liquid water. • When ice freezes on a lake the water freezes from the top down, instead of the bottom up. • Why might this be important for the living organisms in the lake?

21. Weathering • When water freezes, it expands. This phenomenon is responsible for much of Earth’s surface through the process called weathering. • Water seeps into cracks in rocks, and then freezes and thaws with changes in temperature. Over time, this process widens the cracks, breaking off pieces of the rock.

22. Specific Heat • Specific heat is the amount of heat needed to increase the temperature of a certain mass of a substance by 1 degree Celsius. • Water requires a lot of heat to increase its temperature. Meaning water has a HIGH specific heat.