shervette lecture Water Basics students fall08

shervette lecture Water Basics students fall08 - WATER...

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Unformatted text preview: WATER Chapter 6 Properties of Water _____________________________ Is a __________________________ in Ocean Characteristics Plays a major role in global climate, winds, and weather Has some very unique __________ and _________ properties Ocean Waves Fu Chuan-Fu 1 Atomic Structure ______ = basic building block of matter Atoms are composed of several small subatomic particles: Nucleus contains ________ (+) and ________ (no charge) __________ (-) orbit the nucleus Electrical attraction between the positively charged protons and negatively charged electrons holds the electrons in “shells” or layers around the nucleus. A _________ is a group of two or more atoms held together by mutually shared electrons (bonds). Properties of Water Water (H2O) is a molecule composed of two hydrogen atoms tightly bonded to one to oxygen atom; separated by an angle of 105º 105º Water is a ________ molecule; the oxygen end is negatively charged, the hydrogen charged, end is positively charged “Mickey Mouse ears” The _______ nature of water allows two or more water molecules to form to weak “hydrogen bonds”, which hold the molecules together bonds” Surface Tension Hydrogen bonding of Hydrogen water creates a high surface tension surface At its surface water is At deceptively sturdy Surface tension is utilized by some aquatic organisms like the common water skeeter A marine version of the water skeeter is the Sea Skater, Halobates sp. 2 Water on Earth exists in 3 physical states: Solid, Liquid, and Gas Temperature and Density As water cools, its density increases… to a point. The As increases… maximum density of water occurs at 4° C. Consequence: Ice has ~90% of the density of liquid water and thus floats with only ~10% of its mass above water Temperature and Density Another consequence of lower density ice: Bodies of Another water freeze from the top down, not bottom up. • Thus, unless a pond, lake, or bay freezes completely, there will always be liquid water below the ice to allow for living organisms to move and survive winter. Just like ice floats in a glass of cool water, so will warm Just water “float” atop a layer of cold water. Such density float” differences in water can form stable layers within the water column, leading to _____________________. _____________________ Warm water Cool water 3 Heat Capacity of Water ___________ is related to the amount of energy required to increase ___________ the temperature of a substance. Water has a very high heat capacity (nearly 5 times that of aluminum). Water • The outside of a pot heats up way before the water boils • Wet vs. dry sand example Lots of energy is gained or lost to change the temperature of seawater Lots seawater (±1 cal per gm per oC) • However, an additional 540 cal/g must be added to evaporate liquid liquid water (______________________) (______________________) Lots of energy must be lost to freeze the surface. Lots • An additional 80 cal per gram must be removed to change 0oC liquid water to 0oC ice (_______________________) (_______________________) _________________: the thermal properties of water have prevented wide variations in Earth’s temperature, moderating Earth’s climate. This moderated climate is one of the reasons that life on Earth exists, while on Mars it does not. Mars surface Water as a Solvent Water is an excellent solvent of both gases and salts Water This property influences its ability to incorporate This nutrients and dissolve solids; this is why water is such a powerful force for weathering _________________ is the dissolving of the solid _________________ material composing rocks and sediments, which accumulate and are carried by rivers to the ocean, where they contribute to its saltiness 4 Water as a Solvent Easily dissolves compounds with ionic bonds Considered to be a ___________________ Seawater contains dissolved forms of all 92 elements, but not in the same proportions WHY IS THE OCEAN SALTY? 5 Composition of Seawater The 7 most common elements dissolved in seawater: Element/(Ion) % by weight Chloride (Cl-) 55.02 Sodium (Na+) 30.66 Sulfur (SO43-) 7.71 Magnesium (Mg2+) 3.65 1.17 Calcium (Ca2+) +) Potassium (K 1.13 -) 0.30 Carbon (HCO3 Total 99.64 g/1000 g water (salinity in ppt or ‰) 18.980 10.556 2.649 1.272 0.400 0.380 0.140 34.377 The remaining 85 elements are present but in much smaller quantities. ______________ is a measure of the total amount of salts in water Average salinity of seawater is about 34.4 ppt (‰) The Components of Salinity The most abundant ions The most abundant ionic components of a kilogram of seawater Water with more salt has a higher salinity and Water has a greater ability to conduct electricity Water with more salt also has a higher density Water As density increases, the refraction of light As increases proportionately Using this knowledge someone invented the Using _______________, a device that converts the _______________, amount of light refraction into salinity units 6 Refractometer Relationship between Salinity and Density ________________ is a measure of how tightly the molecules of a substance are packed in a given amount of space • Density units are mass per unit volume (e.g. grams/cm3) • Density increases when more mass is packed into a given volume A B Which cube has the highest density? Because salinity is a measure of the amount of dissolved ions in water, the greater number of molecules present in water, the greater the density More on Salinity Salinity • The heat capacity of water decreases with increasing salinity • As salinity increases, freezing point decreases - That is why we pour salt on the ice when we make homemade ice cream • As salinity increases, evaporation slows • Osmotic pressure increases as salinity increases • Is the ocean becoming progressively saltier with age? - No, the ocean is in _____________________ - The proportion and amounts of dissolved solids remain constant, as ions are being added to and removed from the ocean at the same rate. 7 Dissolved Gases • Unlike ions, gases dissolve more readily in cold water than in warm water, and more gas molecules are retained in cold water than in warmer water • Certain dissolved gases are required for life in the ocean (e.g. oxygen and carbon dioxide). • Just 3 gases contribute ~99% of the total dissolved gases in the ocean: More on gases later when we discuss Life in the Oceans Acid-Base Balance What are acids and bases? An _________ is a substance that releases a hydrogen ion in solution. A ___________ is a substance that combines with a hydrogen ion in solution. A solution containing a base is called an ___________ solution. Acidity or alkalinity is measured on the pH scale. Normally, seawater has a pH of ~8 and is kept buffered (resists change) by dissolved CO2 in the water The pH Scale with Comparisons 10-0 10-1 10-2 10-3 10-4 10-5 10-6 10-7 10-8 10-9 10-10 Seawater is slightly alkaline, with a pH of about 8 10-11 10-12 10-13 10-14 8 Some Vertical Features in the Water Column _____________ – a temperature slope with a rapid vertical change over a small amount of depth Halocline - salinity slope with a rapid vertical change ______________ - a density slope with a rapid vertical change in density; is a barrier to mixing Isothermal – depths where water is a constant temperature _______________ – depths where water has the same salinty Isopycnal - horizontal surface with constant density Isohaline region isothermal region isopycnal region Light and Sound Sunlight does not travel well in the ocean, because scattering and absorption weaken light: • ____________ occurs when light is bounced between air and water molecules, dust and other objects such as organisms suspended in the water column. • Absorption (extinction) occurs when light’s electromagnetic light’ energy is converted to heat in the molecules of seawater and objects suspended in the water column. Note: Although the speed of light slows slightly as it enters the water, sound travels up to 5 times faster in water than in air (~ 1.5 km/hr) Absorption (extinction) of light with water depth Turbidity reduces the depth that light can penetrate 9 Light and Sound Light Light and sound both travel in waves. ________________ is the bending of waves, which occurs when waves travel from one medium to another. Refractive index is a ratio that expresses how much a wave ray (like light or sound) is refracted from one medium to another. Sound in the Ocean The science of studying sound in water is called underwater acoustics Sofar layer Like light, sound attenuates with distance traveled through water Low frequency sounds travel the farthest Whales communicate underwater using various frequencies of sound (sonar); their low frequency emissions can be heard The relationship between water depth hundreds of miles from where they originate and sound velocity 10 ...
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