Chapter 8 The Nature of Water Oceanography 2014

Earth: The Water Planet 71% of the Earth’s surface is covered in water Water on Earth 3% freshwater 97% saltwater

Review of the Water Cycle

Review of Atomic Structure Atoms are made of Protons (+) Neutrons Electrons (-) Number of these particles change depending on the element

Water’s Unique Properties Water is a polar molecule A molecule with positively and negatively charged ends Hydrogen (H) atoms bond to oxygen (O) atom with a covalent bond Covalent bond: A bond that is formed by 2 atoms sharing 1 electron O atom shares the electrons of H atoms Water is a very stable molecule because of these bonds

Water’s Unique Properties The 5 Key Effects of Hydrogen Bonds Liquid Water Cohesion/Adhesion Viscosity Surface Tension Ice Floats

The Effects of H-Bonds: Liquid Water H-Bonds require more heat to form steam takes more energy for water to change physical states H-Bonds are why water is liquid at room temperature

The Effects of H-Bonds: Cohesion/Adhesion Cohesion: water molecules attract to each another gives water a more organized structure Adhesion: water molecules “stick” to other materials Example: water droplets cling to a leaf

The Effects of H-Bonds: Viscosity Viscosity is water’s tendency to resist flow Occurs because H-Bonds make water polar Viscosity is inversely related to temperature Temperature increases = Viscosity decreases Temperature decreases = Viscosity increase

The Effects of H-Bonds: Surface Tension Surface tension is water’s resistance to objects breaking its surface Insects that can “walk on water” Polar nature of water allows for the formation of a “skin-like” surface

The Effects of H-Bonds: Ice Floats It’s unusual for the solid state to float in the liquid state most substances get more dense as they cool from liquid to solid Water is different: Ice takes up more space than liquid water Ice: H-Bonds form crystals takes up more room (volume) Ice: same mass as liquid but greater volume Makes ice less dense than liquid water D=M/V

Solutions and Mixtures Solution: A solution occurs when molecules of one substance are evenly spread among the molecules of another substance Solvent: The more abundant substance in the solution Solute: The substance being dissolved Example: Sugar dissolved into water Water is the solvent Sugar is the solute

Solutions and Mixtures, cont. Mixture: A mixture is a combination of 2+ substances that are not chemically bonded Heterogeneous Mixture: Visibly different substances Suspension: Heterogeneous but solute eventually settles Homogeneous Mixture: Looks the same throughout

Salinity Salinity is the concentration of all dissolved inorganic solids, including salt ions Measured with conductivity testing Tool measures electrical current transmitted through a sample to that of a standard Salinity is measured in ratios: there are no units. Expressed in Practical Salinity Scale (PSS) 1/6/13: Period 2 stopping point

Colligative Properties of Seawater Colligative Properties: properties of a liquid that can be changed by the presence of a solute. Increased Boiling Point Decreased Freezing Temperature Presence of Osmotic Pressure -Pressure differential created when a substance exists in differing concentrations on 2 sides of a semipermeable membrane Increased Electrical Conductivity Decreased Heat Capacity (than Freshwater) -How much heat energy it takes to raise 1 gram of a substance 1o C Slowed Evaporation -Attraction of ions & water molecules keeps water from evaporating easily

Dissolved Solids in Seawater Principle of Constant Proportions The principle that the proportions of dissolved elements in seawater are constant. Proportions of Dissolved Solids in 1 kg of seawater, 35 PSS Cl- Chloride 18.98g Na+ Sodium 10.56g SO42- Sulfate 2.65g Mg2+ Magnesium 1.28g HCO3 Bicarbonate 0.14g Ca2+ Calcium 0.40g K+ Potassium 0.38g Other 0.61g

Why the Seas are Salty Oceanic Salinity is stable. Where do the salts come from? Minerals & chemicals flushed in from rivers Eroding coastal rock + and - of materials via hydrothermal vents Biological Factors

Salinity Salinity is affected by rainfall & evaporation The Red Sea (40) and the Mediterranean (38) have higher salinities because Low freshwater input/rainfall High evaporation rate The Black Sea (18) and the Baltic Sea (8) have lower salinities because High freshwater input from rivers Low evaporation rates Ocean has an average salinity of 35

Conditions vary with Ocean Depth Changes Dependent on Depth Ocean water separates into layers because of density differences As you go deeper: Density Increases Temperature & Salinity Decrease

Key Terms Halocline: Abrupt change in salinity that marks two different water layers Thermocline: Temperature transition between a colder/deeper water layer and a warmer/upper layer of water Pycnocline: A thermocline & halocline together creating a boundary between layers of differing water density Period 7 stop point 1/10

pH pH: Scale that represents the balance between the positive hydrogen ions (H+) and the negative hydroxide ions (OH-) of a liquid

pH cont. Acid: higher concentration of H+ ions pH of less than 7 Alkaline (Basic): higher concentration of OH- ions pH of greater than 7 Neutral pH: 7 pure water Seawater range of 7.8 to 8.3

Ions and Charges Ion: the total number of electrons is not equal to the total number of protons, giving the atom a positive or negative electrical charge Sodium (Table Salt): NaCl Cation: ion with a positive charge (Na+) Anion: ion with an negative charge Cl-)

Brackish Water Brackish Water: Area of mixed freshwater and saltwater (low salinity of 0.5-17 ppt) Estuary: area where freshwater and saltwater meet Where river currents meet the ocean Chesapeake Bay

Chemistry of Water: Carbon Carbon = C Fundamental element of life Basis for chemical energy and tissue building Forms found in the ocean CO2 dissolves in water to form carbonic acid

Chemistry of Water: Nitrogen Nitrogen = N Required for: protein chlorophyll nucleic acid Makes up about 48% of dissolved gases in seawater To be used gaseous N must be fixed into: Nitrate (NO3-) Nitrite (NO2-) Ammonium (NH4+)

Chemistry of Water: Nitrogen Oxygen = O Dissolved O levels in seawater vary by Geographical location Biotic factors (algae blooms) Depth Absence of oxygen is called anoxic

Chapter 8 Key Vocabulary Group 1: Water’s Unique Properties Group 3: Inorganic Water Chemistry Polarity Salinity Covalent Bond Brackish Water Hydrogen Bond Halite Cohesion Brine Adhesion Colligative Properties Viscosity Osmosis Surface Tension Semipermeable Membrane Density D=M/V (The mass per unit volume of a substance under certain pressure and temperature) Thermocline Halocline Pycnocline Acid Group 2: Solutions and Mixtures Alkaline Solution Buffer Solvent Group 4: Organic Water Chemistry Solute Nutrients Mixture Denitrification Homogeneous Diffusion Heterogeneous Isotonic Suspension Hypotonic Ions Passive Transport Universal Solvent Active Transport Osmoregulation