CHAPTER 6 - WATER (continued)

Transcription

1 CHAPTER 6 - WATER (continued) Metric Is Beautiful Water freezes at: Water boils at: Fahrenheit 32 ºF 212 ºF Centigrade* 0 ºC 100 ºC *aka the Celsius scale, after its creator, Swedish astronomer Anders Celsius (1742!) Gabriel Fahrenheit, German physicist (who also invented the mercury thermometer), devised his scale in 1714 (so 100ºF = body temperature) Centigrade Temperatures 30 is hot, 20 is pleasing; 10 is not, and 0 is freezing. The 3 States of Matter If you know ºF & want to find ºC: If you know ºC & want to find ºF: Exact formula ºC = ( ºF - 32 ) / 1.8 ºF = ( 1.8 x ºC ) + 32 Approximation (easy way) ºC = ( ºF - 30 ) / 2 ºF = ( 2 x ºC ) + 30 Fig. 6.4, p

2 States of Matter & Bond Strength Gas = Molecules not bonded to one another; move independently. Takes the volume and shape of its container. Liquid = Molecules loosely bonded to one another; bonds easily broken, so liquids flow. Volume is fixed, but takes shape of container. Solid = Molecules strongly bonded to one another; fixed size and shape. Bend or break with applied force. Properties of Water A. The water molecule - Ice, Water, Vapor B. Density & temperature C. Heat & temperature D. Changes of state E. Refraction, light, & sound A. The Water Molecule Element = A substance composed of identical particles that cannot be chemically broken down into simpler substances (e.g., hydrogen) Atoms = The particles that make up elements. Made of protons (p + ), neutrons (n o ), electrons (e ). Molecule = A group of atoms held together by chemical bonds (e.g., O 2 gas) Compound = A substance that contains 2 or more different elements in fixed proportions (e.g., water = H 2 O) Ion = A charged particle (e.g., H + or O 2- ) The Water Molecule If water weren t polar, it would freeze at -90ºC (-130ºF) and boil at -68ºC (-90ºF). And it wouldn t be nearly so good a solvent (dissolver of salts etc). º 2

3 The Water Molecule The Water Molecule Strongly bonded Loosely bonded Not bonded º! Melting!! Evaporation! " Freezing " " Condensation " (ice in glaciers & polar ice caps) (oceans, rivers, & lakes) (water vapor in the atmosphere) Ice The Water Molecule - Types of Bonds Covalent bonds Within each H 2 O molecule Bonds the H s to the O Very strong! (sharing electrons) Hydrogen bonds Hydrogen bonds Between H 2 O molecules Bonds H 2 O molecules to each other Constantly forming and breaking in liquid water 3

4 The Water Molecule - Types of Bonds High surface tension Hydrogen bonding creates skin Important for living organisms Capillarity (e.g., in vascular plants) Fig. 6.2, p. 122 Cohesion The Water Molecule - Types of Bonds Universal solvent Electrostatic bonds between dipolar water and ions Ocean is salty ( NaCl # Na + + Cl ) B. Density & Temperature Density ( $ ) = Mass / Volume (in g/cm 3 ) Ratio, so $ % if mass % or if volume & Relative water density affects watercurrent development Water-density vs. organism-density determines whether an organism will sink or float Some floating organisms can vary their density! Adhesion 4

5 Density & Temperature Density ( $ ) = Mass / Volume (in g/cm 3 ) Most substances get denser (that is, have more mass per unit volume) as they get colder ( T & # $ % ) This is only true for water down to ~4ºC (remember, water freezes at 0ºC) As water cools from ~4ºC to 0ºC, it becomes less dense! ( T & # $ & ) The maximum density of fresh water ( $ max ) is at 3.98ºC Let s draw all that on a graph s draw all that on a graph! Temperature %!! Density %! Density & Temperature Normal substance! Density %! Density & Temperature Water 4ºC! Temperature %! Density & Temperature See Fig. 6.3, p

6 Density & Temperature Density & Temperature Why that funky density peak at 4ºC? 4 Glad you asked!! Liquid water = Made of 2 types of molecular aggregates: Structured aggregates Open, 6-sided structure (~ice), stronger H-bonding Break up and re-form constantly ( times every 1/millionth of a microsecond!) Free molecules Denser packing, weaker bonding Surround the structured aggregates As T! from 4ºC to 0ºC: Molecules begin to line up to form ice crystals = Open, 6-sided structures # Molecules occupy more volume (same mass) # Density & As T! toward 4ºC: Amount of thermal motion & # Molecules occupy less volume (same mass) # Density % C. Heat & Temperature Heat = Energy produced by the random vibration of atoms or molecules A measure of how many molecules are vibrating and how rapidly they re vibrating Temperature = An object s response to an input or removal of heat Records only how rapidly the molecules are vibrating Heat Capacity = a link = The amount of heat required to raise the temperature of 1 gram of a substance by 1ºC Heat & Temperature 1 calorie ' Amount of heat required to raise 1 gram of pure liquid water by 1ºC Water resists changing temperature when it absorbs or releases heat VERY HIGH! º Table 6.1, p

7 D. Changes of State Changes of State Let s s draw all that on a graph Fig. 6.7, p. 126! Temperature %! Solid S & L Water Liquid L & G! Heat %! Gas Changes of State Changes of State! Temperature %! Solid S & L Water Liquid L & G! Heat %! Gas Temperature changes (the water warms as heat is added) when water is totally S or L or G! Temperature %! Solid S & L Water Liquid L & G! Heat %! Gas Temperature doesn t change (T stays same as heat is added) as the water changes state 7

8 Changes of State ) ) At 20ºC (68ºF), latent heat of evaporation = 585 cal/g See Fig. 6.6, p. 126 Global Thermostatic Effects therme = heat; stasis = stay the same Global Thermostatic Effects Water moderates global T s Thermal inertia = Substance resists change in T with gain or loss of heat Water prevents large swings in T Between day and night Between summer and winter 2 cities at same latitude SF s maritime climate! Less extreme T differences Also consider E. WA (desert) vs. W. WA (not!) Fig. 6.8, p

9 Global Thermostatic Effects Global Thermostatic Effects Evaporation removes heat from oceans Condensation adds heat to atmosphere Heat is re-distributed globally Global Thermostatic Effects Global Thermostatic Effects (same distance from Sun) Highest T Lowest T ( Range Earth 57 ºC (123 ºF) -68 ºC (-141 ºF) 125 ºC (264 ºF) Moon 135 ºC (248 ºF) -155 ºC (-280 ºF) 290 ºC (528 ºF) 9

10 E. Refraction, Light, & Sound Refraction Sound & light both travel as waves Refraction = The bending of waves, which occurs when waves travel from one medium to another e.g., from air into water, or between water masses of different densities Refractive index = Ratio that expresses how much the waves are bent Fig. 6.23, p. 140 Light in the Ocean Photic zone = Thin layer of sunlit water at the ocean s surface, generally less than 100 m deep Aphotic zone = The rest Major implications for marine life! Sunlight doesn t travel well in the ocean Scattering - When light is bounced between air and water molecules, suspended sediments, dust, and/or other substances Absorption - When light s electromagnetic energy is converted to heat in the ocean water molecules Light in the Ocean Not all wavelengths (colors) of light are absorbed the same amount by water Blue light penetrates deeper than any other color Wavelength % absorbed Color (nm) in 1st meter I.R. Red Orange Yellow Green Blue Violet U.V Depth 99% absorbed Fig. 6.21a&b, p

11 Light in the Ocean Speed of light: In water ~223,000 km/sec In air ~300,000 km/sec! The speed of light in water is only ~3/4 its speed in air Sound in the Ocean Relationship between water depth and sound velocity Note the region of minimum sound speed at ~1000 m depth Refraction tends to keep sound waves within this layer (SOFAR* layer) *SOund Fixing And Ranging Fig. 6.22, p. 139 The SOFAR Layer The SOFAR Layer It s efficiency, not speed, that matters Fig. 6-24, p

12 SONAR (SO SOund Navigation And Ranging) SONAR Fig. 6.25, p. 141 Side-Scan SONAR Multibeam System See Fig. 6.26, p. 142 Light vs.. Sound in the Ocean Speed of sound: In water ~1500 m/sec In air ~330 m/sec! Speed of sound in water is ~5x its speed in air Which travels deeper: light or sound? (Hint: Check your notes) Which travels faster: light or sound? Let s do a little calculation (Hint: Keep track of units!) Light vs.. Sound in the Ocean Which travels deeper in the ocean: light or sound? Light ~100 m (photic zone) Sound >3000 m (see scale on figure) 3000 m = (?) x 100 m 3000 m / 100 m = (?) " Sound travels >30 times deeper than light in ocean Which travels faster in the ocean: light or sound? Light ~223,000 km/sec Sound ~1500 m/sec = ~1.5 km/sec 1000 m = 1 km, so 1500 m = 1.5 km 223,000 km/sec = (?) x 1.5 km/sec 223,000 km/sec / 1.5 km/sec = (?) " Light travels 150,000 times faster than sound in ocean 12

13 Next Time SALINITY SALINITY Fig. 6.12, p Minute Write Summarize the main points of today s lecture. List 3 to 5 questions you have, based on today s s lecture. What did you find most interesting about today s s lecture? How was the lecture relevant to you? Fig. 6.1, p