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Physical and Chemical Properties of Water

Physical and Chemical Properties of Water. The Water Molecule. Water is a compound Compound: substance that contains two or more different elements. H 2 O: 2 hydrogens and 1 oxygen A water molecule is held together by a Covalent Bond. Molecules are held together by shared electrons.

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Physical and Chemical Properties of Water

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  1. Physical and Chemical Properties of Water

  2. The Water Molecule • Water is a compound • Compound: substance that contains two or more different elements. • H2O: 2 hydrogens and 1 oxygen • A water molecule is held together by a Covalent Bond. • Molecules are held together by shared electrons. • 2 or more water molecules are held together by Hydrogen bonds • Hydrogen Bond-When a hydrogen atom is linked to another atom by electrostatic forces. Much stronger than covalent bonds. • Gives water properties such as cohesion and adhesion.

  3. A Polar Molecule • Molecule behaves like a magnet. • Its positive end attracts negatively charged particles • Its negative end attracts positively charged particles • Most salts are held together by opposite charges (Na+, Cl- is NaCl) and when these come in contact with water, they are pulled apart. • This is why water is a good Solvent (dissolve things well).

  4. Properties of Hydrogen Bonding • Cohesion-Allows individual water molecules to stick to each other (cluster), giving water a high surface tension. It also allows for diffusion. (think of the water on the penny or paper clip on water…this is due to cohesion and surface tension). • Adhesion-The tendancy of water to stick to other materials (making them wet). (capillary action in soil or water running up a paper towel).

  5. Physical Properties of Ocean Water • Heat Capacity • Temperature • Density • Salinity • Ability to transmit light • Ability to transmit sound

  6. Heat Capacity • Heat: A measure of energy produced by vibration of atoms or molecules. • Temperature: A measure of how rapidly molecules are vibrating. • Heat Capacity: The amount of heat it takes to raise 1 gram of a substance by 1 degree Celsius. • Water has highest heat capacity of any substance. • From hydrogen bonding! • Means water’s temperature does not rise or lower very easily.

  7. Measuring Heat • Calories per gram • Heat=Specific Heat x Change in Temperature • How would we calculate Specific Heat?

  8. Temperature and Density • Water becomes more dense as it gets colder. • UNTIL: It reaches 4 degrees Celsius. • Then water becomes less dense as it freezes • Why does this happen? Hint: Density=Mass/Volume

  9. Salinity and Density • Note that a higher salinity gives water a higher density. • Note also that salinity decreases the temperature at which water freezes • So ocean water freezes at about -2 degrees Celsius • Fresh water freezes at 0 degrees Celsius

  10. Temperature, Salinity, Density 10 C 12 PPT 1.010 g/cm3 21 C 15 PPT 1.010 g/cm3 Note that two samples of water can have the same density at different combinations of temperature and salinity.

  11. Density Summary • Density of Seawater is 1.020-1.030 g/cm3 • Fresh is only 1.000 g/cm3 • Cold, salty water is more dense than warm, less salty water. • Seawater’s density increases with increasing salinity, increasing pressure, and decreasing temperature (until right before it freezes). • Two samples of water can have the same density at different combinations of temperature and salinity.

  12. Light in the Ocean -Long wavelengths are absorbed at shallow depths. -Blue light penetrates to the deepest levels and is reflected back -To our eyes. this is why the oceans appear blue.

  13. Photic Zone • Photic Zone: The depth light penetrates in the ocean. • 200 meters in clear, tropical waters • 100 meters in most ocean waters • All photosynthetic organisms live in this zone (corals, sea grasses, algae, phytoplankton). • Infrared radiation is converted to heat • Most of life in the ocean is found here.

  14. Aphotic Zone • Aphotic Zone: Zone below photic zone that is in complete darkness. • About 1% of light penetrates to a depth of 100-125 meters • Absolutely no light penetrates below 1,000 meters. • ¾ or 75% of the ocean is in total darkness!

  15. Refraction • Refraction: Bending of waves. Light acts as a wave and a particle. Light bends toward The normal When it travels From a lower Density to higher Density. Light bends away from The normal when it Travels from higher density To lower density.

  16. Snell’s Law Nair=1 Nwater=0.75

  17. Sound in the Ocean • Sound: Form of energy transmitted through a medium through vibration of molecules. • Sound intensity decreases through seawater due to spreading, scattering, and absorption. • Sound travels about 1,500 m/s in seawater • Sound travels 334 m/s in air at 20 degrees C. • Speed of sound increases as temperature, pressure, and salinity increase. • Low frequencies travel farther than high frequency

  18. Sofar Layer • The minimum velocity layer • 1200 m depth in North Atlantic down to 600 m depth in North Pacific • Sound waves move at minimum speed and allow for sounds to heard for great distances since refraction keeps sounds waves within the layer.

  19. Shadow Zones 80 M Maximum sound velocity occurs at 80 m which deflects sound and causes a shadow zone.

  20. SONAR • SONAR: Sound Navigation and Ranging.

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