Download Chapter 6 Nature of Water PPNT

Journal #2
• What are two things you know about water?
• What are two things you want to know about
water?
Chapter 6
The Nature of Water
The Water Planet
• Water covers about 71% of the Earth’s surface.
• The world’s oceans provide more than 99% of the
Earth’s biosphere: the habitable space on earth.
• A majority of the water on this planet cant be
used directly for drinking, irrigation, etc. because
most of it is salt water.
• As the population on Earth increases so does the
need for water.
How do we meet the demand for
water?
• What is it?
• Where does it go?
• How does it cycle in nature?
Water’s Unique Properties
• Water as a simple molecule:
– Its structure gives the unique properties
– Hydrogen atoms---Oxygen atoms by a covalent bond
(sharing of electrons); makes water very stable
• A molecule with a positive (hydrogen end) and
negative (oxygen end) end has polarity. This is called
a polar molecule.
- This enables water to bond with other water
molecules.
- Positive hydrogen end attracts negative oxygen end.
- This bond that forms is known as a hydrogen bond
(weak alone, strong in large numbers).
Why a polar molecule?
• Liquid water: Due to the hydrogen bonds, water is able
to be a liquid at room temperature. Otherwise, water
would be a gas.
• Cohesion/adhesion: Due to hydrogen bonds and
polarity, water molecules tend to stick to one another;
this is COHESION. When water molecules stick to other
things this is called ADHESION.
• Viscosity: Tendency for a fluid to resist flow. Colder
water= more viscous ex: oil in a frying pan
• Surface Tension: a skin-like surface formed due to the
polar nature of water. Water’s resistance to organisms
trying to break through the surface.
Why a polar molecule?
• Why does ice float?
- When water cools, goes from liquid to solid.
- Hydrogen bonds spread out into crystal
structure, taking up more space than in liquid
form
- Ice floats
- What would happen if ice sank?
Solution vs. Mixture
• Solution: molecules of one substance are
homogeneously dispersed among the
molecules of another substance (seawater)
- Solute: the substance being dissolved
- Solvent: the substance doing the dissolving
(water)
• Mixture: when two or more substances
closely intermingle, yet retain their individual
properties. (chexmix)
Salts and Salinity
• Salinity: total quantity of all dissolved
inorganic solids in seawater
• Sodium Chloride is the most abundant sea
salt
• Scientists measure the salinity in many ways
• Varies from no salinity near mouths of rivers
to more salinity in confined, arid regions of
ocean
Colligative Properties:
• Properties of a liquid that may be altered by the
presence of a solute and are associated primarily with
sea water (pure water has none)
• They include:
–
–
–
–
–
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Ability to conduct an electrical current (electrolyte)
Decreased heat capacity (less heat to raise temp)
Raised boiling point
Decreased freezing temperature
Slowed evaporation: due to attraction of molecules
Ability to create osmotic pressure: Osmosis: water
molecules moving from high concentration to low
concentration. Water moving in= raises osmotic pressure
The Principle of Constant Proportions
• In seawater, no matter how much the salinity
varies, the proportion of several key inorganic
elements and compounds NEVER change.
• Only the amount of water and salinity
changes
Why are the Seas Salty?
• Source of salts seems to come from eroding
minerals and chemicals that dissolve in fresh
waters that flow into the ocean. (waves
contribute to this as well)
• Belief that all of these factors counterbalance,
keeping salinity of the ocean fairly constant
• Ocean is said to be in chemical equilibrium.
Salinity and Temperature
• Precipitation vs. Evaporation
- Rainfall decreases salinity by adding fresh
water
- Evaporation increases salinity by removing
fresh water
- Fresh water input from rivers lowers salinity.
• Salinity and Temperature also vary with depth
Water Density
• Low temperature + high salinity = high density
• Warm, low-density surface waters are separated
by the cool, high-density deep waters by the
thermocline: the zone in which temperature
changes rapidly with depth
• Salinity differences overlap temperature
differences and the transition from low-salinity
surface waters to high-salinity deep waters is
known as the halocline.
• Both together make the pycnocline: zone where
density increases as depth increases
Acidity and Alkalinity
• Concentration of positively charged hydrogen
ions or negatively charged hydroxide ions
determines waters acidity or alkalinity.
• Measured as pH: when solution has many
hydrogen ions, considered an acid with a pH
value of 0 to less than 7; when solution has a pH
value of more than 7 considered a base (lots of
hydroxyl ions; called an alkaline)
• pH of seawater is relatively stable, but changes
slightly with depth because the amount of carbon
dioxide also varies with depth. Why is this?
Biogeochemical Cycles
• Organisms require certain elements and
compounds in order to stay alive
- Primary nutrient elements related to seawater
are: carbon, nitrogen, phosphorus, silicon,
iron, and other trace elements.
- Not all these nutrients cycle at the same rate;
this affects the nature of organisms and where
they live in the sea
Carbon Cycle
Nitrogen Cycle
Water Cycle
What factors of water affect marine
life?
• Diffusion and Osmosis:
- Diffusion: Moving from high concentration to low
concentration
- Osmosis: diffusion of water moving from areas of high
concentration to low concentration
• Hypertonic: water moves from inside (high) the cells to
outside the cells (low). Ex: putting a freshwater fish into a
marine environment
• Isotonic: water molecule concentration is equal on both
sides (marine fish in seawater)
• HypOtonic: water moves from outside the cells to inside
the cells causing them to burst. Ex: placing a marine fish
into a fresh water environment (cells will burst in the fish)
Active Transport, Osmoregulators,
Osmoconformers
• Osmosis- type of passive transport moving water
molecules from high to low. NO ENERGY
• Active Transport: Moves molecules from low to high
and REQUIRES ENERGY
- Goes against the flow of diffusion
• Osmoregulators: Marine fish have ability to regulate
water concentration in their cells using active
transport; Adapt to changes in salinity
• Invertebrates cant control their internal water
concentration. Internal salinity rises and falls as salinity
rises and falls in the surrounding seawater. These
organisms are called osmoconformers.
Daily Quiz # 1
1) What does it mean to be polar? What does
polarity do for water molecules?
2) Where does the salts in the ocean come
from?
3) Differentiate between hypertonic and
hypOtonic. How does this affect marine life?