SEAWATER and the properties of the water molecule

The form of the H 2 O molecule determines its behavior One hydrogen H and two oxygen O atoms bonded by sharing electrons One hydrogen H and two oxygen O atoms bonded by sharing electrons Both H atoms make a positive side, O side is negative, so it is a: Polar molecule Both H atoms make a positive side, O side is negative, so it is a: Polar molecule

Hydrogen bonding Polarity means small negative charge at O end Polarity means small negative charge at O end Small positive charge at H end Small positive charge at H end Attraction between + and – ends of water molecules to each other or other ions Attraction between + and – ends of water molecules to each other or other ions Fig. 5.3

Effects of hydrogen bonding: the result of polarity Hydrogen bonds are weaker than covalent bonds but still strong enough to result in: Hydrogen bonds are weaker than covalent bonds but still strong enough to result in: 1. High surface tension 2. Cohesion and adhesion 3. High solubility of chemical compounds in water 4. Solid, liquid, gas at Earth’s surface 5. Unusual thermal properties 6. Unusual density

Water molecules in different states of matter Fig. 5.5

Putting heat in perspective Heat is energy of moving molecules Heat is energy of moving molecules Calorie is amount of heat needed to raise the temperature of 1 gram of water by 1 o C Calorie is amount of heat needed to raise the temperature of 1 gram of water by 1 o C Temperature is measurement of average kinetic energy Temperature is measurement of average kinetic energy

Fig. 5.6 Effect of heat input on temperature

Unusual thermal properties of H 2 O H 2 O has high boiling point H 2 O has high boiling point H 2 O has high freezing point H 2 O has high freezing point High latent (hidden) heats of High latent (hidden) heats of Vaporization/condensation Vaporization/condensation Melting/freezing Melting/freezing Evaporation Evaporation

Unusual thermal properties of H 2 O Water high heat capacity Water high heat capacity Which is the amount of heat required to raise the temperature of 1 gram of any substance 1 o C, also called “specific heat” Which is the amount of heat required to raise the temperature of 1 gram of any substance 1 o C, also called “specific heat” Water can take in/lose lots of heat without changing temperature much Water can take in/lose lots of heat without changing temperature much Rocks low heat capacity Rocks low heat capacity Rocks quickly change temperature as they gain/lose heat Rocks quickly change temperature as they gain/lose heat

Specific Heat Values Specific Heat Material(cal/g °C)(J/kg K) Aluminum Copper Iron Lead Brass Magnesium Zinc Styrofoam Air Water Ice

Global thermostatic effects Moderate temperature on Earth’s surface Moderate temperature on Earth’s surface  Equatorial oceans (hot) don’t boil  Equatorial oceans (hot) don’t boil  Polar oceans (cold) don’t freeze solid  Polar oceans (cold) don’t freeze solid Marine effect Marine effect Oceans moderate temperature changes day/night; different seasons Oceans moderate temperature changes day/night; different seasons Continental effect Continental effect Land areas have greater range of temperatures day/night and during different seasons Land areas have greater range of temperatures day/night and during different seasons

Density of water due to temperature Density of water increases as temperature decreases, until it gets to 4 o C to 0 o C (ice) density of water decreases as temperature decreases Density of water increases as temperature decreases, until it gets to 4 o C to 0 o C (ice) density of water decreases as temperature decreases Density of ice is less than density of water Density of ice is less than density of water

Density of water Fig. 5.10

Density of Various Materials Materialg/cm 3 Aluminum2.7 Copper8.96 Iron7.87 Lead11.3 Brass8.4 Magnesium1.74 Zinc7.14 Lead11.3 Water1.00 Ice0.917

Salinity Total amount of solid material dissolved in water- Traditional definition Total amount of solid material dissolved in water- Traditional definition Typical salinity is 3.5% or 35 o /oo Typical salinity is 3.5% or 35 o /oo o /oo or parts per thousand (ppt) = grams of salt per kilogram of water g/Kg Six elements make up 99% of dissolved solids in seawater Fig. 5.12

Measuring salinity Can be measured by specific gravity, electrical conductivity or by refraction of light Can be measured by specific gravity, electrical conductivity or by refraction of light We will measure with a refractometer in parts of salt per thousand of water (the unit being ppt or 0/00) We will measure with a refractometer in parts of salt per thousand of water (the unit being ppt or 0/00) 2% would be equal to 20 0/00 2% would be equal to 20 0/00

Salinity variations Open ocean salinity 33 to 38 o /oo Open ocean salinity 33 to 38 o /oo Coastal areas salinity varies more widely Coastal areas salinity varies more widely Influx of freshwater lowers salinity or creates brackish conditions Influx of freshwater lowers salinity or creates brackish conditions Greater rate of evaporation raises salinity or creates hypersaline conditions Greater rate of evaporation raises salinity or creates hypersaline conditions Salinity may vary with seasons (dry/rain) Salinity may vary with seasons (dry/rain)

Processes that add/subtract water from oceans Precipitation (rain or snow) Precipitation (rain or snow) Runoff (river flow) Runoff (river flow) Melting icebergs Melting icebergs Melting sea ice Melting sea ice Evaporation Evaporation Formation of sea ice Formation of sea ice Salinity decreases through: Salinity increases through:

Deep ocean variation of salinity Surface ocean salinity is variable Surface ocean salinity is variable Deeper ocean salinity is nearly the same (polar source regions for deeper ocean water) Deeper ocean salinity is nearly the same (polar source regions for deeper ocean water) Halocline, rapid change of salinity with depth Halocline, rapid change of salinity with depth

Salinity versus depth Fig. 5.22

Hydrologic cycle describes recycling of water near Earth’s surface Fig. 5.15

Surface ocean variation of salinity…why? Fig. 5.21

Surface ocean variation of salinity Polar regions : salinity lower, lots of rain/snow and runoff Polar regions : salinity lower, lots of rain/snow and runoff Mid-latitudes : salinity higher, high rate of evaporation Mid-latitudes : salinity higher, high rate of evaporation Equator : salinity lower, lots of rain Equator : salinity lower, lots of rain Thus, salinity at surface varies primarily with latitude Thus, salinity at surface varies primarily with latitude

What else affects DENSITY (besides salinity)?

TEMAPERATURE affects DENSITY Density seawater controlled by temperature, Density seawater controlled by temperature, Most important influence is temperature Most important influence is temperature Density increases with decreasing temperature, as more molecules can pack tightly when not moving as much Density increases with decreasing temperature, as more molecules can pack tightly when not moving as much Ocean layered according to density Ocean layered according to density to g/cm 3 surface seawater to g/cm 3 surface seawater Salinity greatest influence on density in polar oceans Salinity greatest influence on density in polar oceans Polar ocean is isothermal Polar ocean is isothermal

Our ocean is layered due to density differences at depth Pycnocline, abrupt change of density with depth Pycnocline, abrupt change of density with depth Thermocline, abrupt change of temperature with depth Thermocline, abrupt change of temperature with depth Halocline, abrupt change of salinity with depth Halocline, abrupt change of salinity with depth High latitude oceans High latitude oceans Isothermal Isopycnal

Fig. 5.23

Lastly…sound and light of seawater Due to density, the speed of sound in salt water is 1500 m/sec Due to density, the speed of sound in salt water is 1500 m/sec As opposed to 340 m/sec in air As opposed to 340 m/sec in air The index of refraction of light in water is 1.33, as you increase the salinity, you increase the index The index of refraction of light in water is 1.33, as you increase the salinity, you increase the index

Residence time and steady state Fig. 5.16

Carbonate buffering Keeps ocean pH about same (8.1) Keeps ocean pH about same (8.1) pH too high, carbonic acid releases H+ pH too high, carbonic acid releases H+ pH too low, bicarbonate combines with H+ pH too low, bicarbonate combines with H+ Precipitation/dissolution of calcium carbonate CaCO 3 buffers ocean pH Precipitation/dissolution of calcium carbonate CaCO 3 buffers ocean pH Oceans can absorb CO 2 from atmosphere without much change in pH Oceans can absorb CO 2 from atmosphere without much change in pH

Fig Carbonate buffering

Acidity and alkalinity Acid releases H+ when dissolved in water Acid releases H+ when dissolved in water Alkaline (or base) releases OH- Alkaline (or base) releases OH- pH scale measures the hydrogen ion concentration pH scale measures the hydrogen ion concentration Low pH value, acid Low pH value, acid High pH value, alkaline (basic) High pH value, alkaline (basic) pH 7 = neutral pH 7 = neutral

Can you drink seawater? No, it will make your cells plasmolyze and you will die. But we now can remove salt from seawater No, it will make your cells plasmolyze and you will die. But we now can remove salt from seawater Distillation--most common process Distillation--most common process Electrolysis Electrolysis Reverse osmosis Reverse osmosis Freeze separation Freeze separation

Fig. 5.24