1. Topic 8 Properties of Water GEOL 2503 Introduction to Oceanography

2. H20H20 Englishman, Sir Humphrey Davey discovered the formula for water: H 2 O 3 Atoms: two hydrogen & one oxygen H+ H+ O 2- 2

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4. Polar Molecule Positive end –Hydrogens on tips of “V” Negative end –Oxygen on other end Molecules attract one another 4

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6. Properties of Water Thermal (Heat Capacity) Cohesion Surface Tension Viscosity Transmission of light, sound 6

7. Thermal Properties of Water Phase changes Heat capacity 7

8. Changes of State Solid - ice Liquid – liquid water Gas -water vapor Water is the only common substance to exist in all three states of matter at normal Earth surface temperatures 8

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10. January 8, 2010; 8 AM 10

11. January 8, 2010; 2 PM 11

12. To change a state of matter Need time to add or remove heat Need time for the hydrogen bonds to break 12

13. Pure Water 100 % water—nothing else No suspended particles No dissolved substances including gases 13

14. State Change Temperatures Pure water melts/freezes at 0° C (32 ° F) Pure water boils/condenses at 100 ° C (212 ° F) –[at standard air pressure] 14

15. For example: Take solid water (ice) Add heat Temperature rises above freezing point Ice melts Forms liquid water 15

16. Another example: Start with liquid water Add heat Temperature rises Water evaporates to form gaseous water (water vapor) 16

17. Also works in reverse: Start with water vapor (gas) Remove heat (cool) Temperature falls Water vapor condenses to form liquid water Remove more heat Freezing Solid water (ice) forms 17

18. Heat is not the same as temperature

19. What is Heat? Heat is energy Measured in calories A calorie is the amount of heat needed to raise the temperature of 1 gram of water by 1° C [Kcal (1000 calories) = 1 food calorie] 19

20. Remember: It takes 1 calorie of energy (heat) to raise the temperature of 1 gram of liquid water by 1° C Also, if you remove 1 calorie of energy the temperature of 1 gram of liquid water will then drop 1° C 20

21. But look at state (phases) changes: To change 1 gram of ice at 0° C to liquid water at 0° C Requires 80 calories per gram not 1 calorie Called the latent heat of fusion 21

22. And: To change 1 gram of liquid water at 100° C to gas (water vapor) at 100° C Requires 540 calories per gram not 1 calorie Called the latent heat of vaporization 22

23. Why? Not changing temperature Breaking chemical bonds That takes energy (heat) Works in reverse by taking heat away (chemical bonds are formed) 23

24. Solid Liquid Gas 24

25. A--hydrogen bond B--oxygen atom C--hydrogen atom D--positively charged side of the water molecule E--negatively charged side of the water molecule 25

26. State Change Terminology Solid to liquid: melting Liquid to gas: evaporation Gas to liquid: condensation Liquid to solid: freezing Solid to gas: sublimation Gas to solid: deposition 26

27. Heat Capacity Is defined as the quantity of heat required to produce a unit change of temperature in a unit mass of that material Heat capacity of water is 1 calorie per gram per degree Celsius Heat capacity of water is higher than most other liquids due to hydrogen bonding 27

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29. Heat capacities: Liquid water = 1 cal/g/ºC Ice = 0.5 cal/g/ºC Water vapor = 0.5 cal/g/ºC How many calories does it take to raise the temperature of 1 gram of water from -100 ºC to +150 ºC ? 29

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31. High heat capacity helps move heat around the Earth, moderating climate Water evaporates from oceans, absorbing heat from oceans Winds move water vapor Water returns to liquid form by precipitation, adding heat to the atmosphere 31

32. Range of normal Earth Temperatures controlled by latent heat Deserts +50° C (122° F) Antarctica -50° (-58° F) –Land range 100° C (180° F) Tropical oceans +28° C (82° F) Polar oceans -2° C (28° F) –Ocean range 30° C (54° F) 32

33. Land versus Ocean Temperatures Land: –+50° C (122° F) to -50° (-58° F) –Land range 100° C (180° F) Water: –+28° C (82° F) to -2° C (28° F) –Ocean range 30° C (54° F) 33

34. “Evaporation is a cooling process” You’ve probably heard that phrase To evaporate water takes 540 calories of heat per gram Essentially absorbing heat Example—cooling our bodies (removing heat energy) by evaporation of perspiration 34

35. Heat Capacity Summary: Day/night change of water temperature is very small Helps redistribute heat around Earth Helps stabilize Earth’s surface temperatures 35

36. Cohesion Water has more structure than other liquids due to the hydrogen bonds - hold water together Water molecules stay close together due to polarity Makes water relatively sticky 36

37. Surface Tension Water molecules form a film because of sticky nature of water Paper clip floats, water striders Overfill glass of water High surface tension is important for waves Decrease temperature increases surface tension and vice versa 37

38. Viscosity Resistance to flow High viscosity means high resistance to flow Affected by temperature—“slow as molasses in January” 38

39. Density Less dense floats on denser liquids Example: Ocean water is denser than fresh water so fresh floats on salt water Defined: mass per unit volume of a substance Measured in grams per unit centimeter cubed 39

40. What is mass? Mass is the amount of matter present It is not the same as weight Weight changes depending on gravity Mass remains constant Think of astronauts—normal weight on Earth, weightless in space, 1/6 th of Earth weight on moon, but their mass is constant 40

41. Density Pure water: D = 1.0000 g/cm 3 –At 4° C (39.2° F) Sea water has salt dissolved in it, so it is denser than pure water Sea water: D = 1.0278 g/cm 3 –At 4° C (39.2° F) 41

42. Coke Can Density Experiment Can of regular Coke sinks in water Same size can of Diet Coke floats WHY? 42

43. Effect of Temperature on Density As heat is added, molecules move faster and move farther apart End up with less mass per unit volume Therefore, as temperature increases, density decreases 43

44. Less dense substances float on denser substances Dry pine wood floats on water Oil floats on water Fresh water floats on salt water Warm water floats on cold water 44

45. Ice and Density As pure water cools, density increases Maximum D at 4° C ( D = 1 g/cm 3 ) Below 4° C solid crystal ice structure starts to form and molecules are pushed apart Same mass but occupying larger volume so lower density Ice is 10 % less dense than water at 4° C Ice floats 45

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47. Note how water molecules are farther apart than in liquid water 47

48. Effect of Salt on Density Dissolved materials increase density of water (more mass per unit volume) Pure water: D = 1.000 g/cm 3 Fresh water: D ≈ 1.000 g/cm 3 Sea water: D = 1.0278 g/cm –[at 4° C] 48

49. Pressure Increases with depth For every 10 m (33 ft.) in depth the pressure increases by 1 atmosphere 1 atmosphere = 14.7 pounds per square inch 49

50. Water = Universal Solvent Essentially everything dissolves in water 50

51. Light Visible light is narrow band of electromagnetic spectrum Visible light is broken into rainbow ROY G BIV Red absorbed within 33 ft. in ocean Blue-green light spectrum goes deeper Objects seen in natural color at the surface Objects in deeper water appear dark because illuminated by blue light 51

52. Violet Blue Green Yellow Orange Red The Electromagnetic Spectrum Gamma Rays X-Rays Ultraviolet Visible Light Infrared Rays Microwaves Radar Short Wave FM TV Broadcast Band Long Radio Waves 52

53. Visible Light & Seawater 60% is absorbed in 1st meter 80% is absorbed by 10 m (33 ft) 99% is absorbed by 150 m (500 ft) 100% is absorbed by 1000 m (3300 ft) 53

54. Why is the Sea Blue? Color = reflected light Red end of spectrum absorbed Blue-green end reflected back We see the reflected blue end of the spectrum ROY G BIV AbsorbedReflected back 54

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56. Transmission of light in water is measured using a Secchi disk 56

57. The Secchi Disk measures water clarity. Simply lower the disk and record water depth at which you can no longer see it. Very low-tech, but effective measure. 57

58. Sound Travels faster in water than air Velocity 1500 m/s (5000 ft/s) In dry air 334 m/s (1100 ft/s) Speed increases if –Temperature increases –Pressure increases –Salt increases 58

59. PDR and DSL PDR = Precision depth recorder Uses narrow sound beam traces bottom while ship is in motion Echo Finders = fish finders DSL = Deep Scattering Layer Organisms/fish found by depth recorders (creates false bottom on depth recorder) 59

60. SONAR (Sound Navigation & Ranging) Underwater location system Locates objects and finds targets Echo reflected from target Sound shadows formed Sound changes speed as passes through different densities of water 60

61. SOFAR Sound Channel Sound is transmitted more effectively and rapidly in water than it is in air Sound velocity in the ocean is about 1500 m/s, or about 4-5 times that in air Sound is focused into the SOFAR channel because of its low velocity region Sound is transmitted best through this channel -- important for submarines and cetaceans 61

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63. SOFAR Channel Experiments 63