Properties of Water

1. Properties of Water Water and Ocean Structure

2. The Water Molecule • H2O = 1 oxygen atom and 2 hydrogen atoms • Atoms are linked by covalent bonds • Polar molecule with hydrogen atom positively charged; oxygen atom negatively charged. • This polarity causes an attraction between neighboring molecules

3. Dissolving Property of Water • Positive hydrogen ion attracts negative chlorine ions; negative oxygen ion attracts positive sodium ion • Water’s dissolving ability related to molecular structure • Water separates compounds held together by opposite electrical charges, i.e. salt (Na+ + Cl-)

4. States of Water • Water is only substance that naturally occurs in all 3 states • Heat is a measure of how many molecules are vibrating and how fast • Temperature is a measure of how rapidly the molecules are vibrating • Thus, addition or loss of heat changes water’s physical property

5. Latent Heat • Latent Heat of Fusion • Latent Heat of Vaporization • Amount of heat needed to change from a solid to a liquid • Amount of heat needed to change from a liquid to a vapor

6. Latent Heat • Latent heat of vaporization (evaporation) is far greater than latent heat of fusion (melting). • Water - freezes 0°C; boils 100°C • All of the H bonds between H20 molecules must be broken to form vapor

7. Heat Capacity of Water Heat Capacity for Common Substances • Ability of a substance to change temperature with a given amount of heat • Water has a very high heat capacity compared to land • High heat capacity causes slow temperature changes in world’s ocean • Helps keep the Earth’s surface temperature stable

8. Heat Capacity of Water

9. Viscosity of Water • The resistance of fluid to flow • Water has low viscosity Exxon Valdez 1989 • Affected by temperature • Surface water at equator is warmer and less viscous than Arctic

10. Surface Tension of Water • Lateral and downward attraction between individual molecules • Creates a strong boundary at surface • ↑ salt = ↑ surface tension • ↓ H2O temp = ↑ surface tension Water strider

11. Unique Property of Water Why does ice float on water? • When liquid H20 loses heat and temperature lowers to freezing point, ice forms • Water expands as it freezes • Angle between H and O atoms in H20 molecule increases from 105° to 109° • Ice less dense than water – ice floats

12. Density of Water Density of water is affected by: • Temperature • As water first cools, density increases and volume decreases • Below 4°C, density decreases • At 0°C, ice forms, density decreases rapidly • Salinity • Adding salts increasesdensity • Fresh H20 floats on salt H20

13. Density of Water

14. Compressibility of Water • Substance’s ability to undergo volume changes • Water has slight compressibility • # of molecules/unit volume does not change much

15. Transmission of Light Why is the ocean blue? • Photic zone – maximum light penetration • Intensity of light decreases with depth • 65% of light absorbed in 1st m • Only 1% reaches 100 m • No visible light below 1,000 m • Water absorbs red, orange, yellow and ultraviolet wavelengths • Only blue light remains where it is reflected and scattered

16. Transmission of Light • As light passes from less dense air to more dense water, it changes speed and bends • Refraction • Light travels faster through water than air

17. Transmission of Sound • Sound travels faster in water • Sound velocity in water = 1,500 m/sec (5x greater than in air) • Sound speed increases with pressure, temperature and salinity • Use sound with sonar

18. Sound and Locating Objects • When sound speed decreases with depth, waves are bent downward • When sound speed increases with depth, waves are bent upward • An area exists where no sound waves travel – shadow zone