Properties of Water
Video Notes http://www.youtube.com/watch?v=2vfld5 yk4lm (1:26) http://www.youtube.com/watch?v=ivu4nl vd_90 (4:37) https://www.youtube.com/watch?v=0ens nj4zfz8#t=4.4600086 (4:58) new
H 2 O is a small molecule That plays a vital role in Earth s ecology It behaves differently than other compounds
Density Most compounds are more dense in solid form. Water is LESS dense as a solid. List one advantage **Ice covers the top of water, allowing marine life to survive underneath.
Density Why is H 2 O LESS dense when solid? The molecules are spread farther apart when they are frozen. Ice Water
Water is Polar There is an uneven distribution in charge. The hydrogen side is slightly positive The oxygen side is slightly negative This polarity causes a strong hydrogen bond
Hydrogen Bonding Opposites attract! The positive hydrogen end of one molecule is attracted to negative oxygen end of another molecule Very strong bond!
Hydrogen Bonds These bonds are so strong, that in order for H 2 O to change from a liquid to a gas, the hydrogen bonds must be broken! It takes a lot of energy to do this This is why water has a high boiling point (it requires more heat energy than molecules similar in size).
Quick Check What must happen for water to change from a liquid to a gas?
At sea level, H 2 O remains liquid 0-100 o C 32-212 o F
Aqueous Solutions The oceans are the largest aqueous solutions!
Solutions of Water Most water is not pure, it comes in a type of solution A mixture of water and another element(s) Ocean water is an aqueous solution A mixture of salt dissolved in water
Think pair - share What does salt do to the boiling point, freezing point, and density of water?
Salty Differences? Salt concentration will change the density, boiling point, and freezing point More salt = increases density increases boiling point temp decreases freezing point temp (That s why they sprinkle salt on sidewalks and roads after heavy snow and ice)
Consider this: Discuss these with the person next to you. Does it take more energy to change the state of pure water or ocean water (between solid/liquid/gas)? What are the pros and/or cons of this? Ocean water is liquid generally -2 to 100.3 o C 28.4 to 212.5 o F
Properties of Ocean Water Salinity
Two Important Factors Salinity the measure of the dissolved salts in water. Temperature the heat energy contained in water.
Measuring Salinity Evaporate the water and weigh the salt that remains. Salinity = Mass of salt/mass of water sample Expressed as a % (parts per hundred) Since salinity in seawater is low, we state it in parts per thousand (%0) Seawater = 35%0 generally
Measuring Salinity Oceanographers measure electrical conductivity Ions dissolved in seawater enable an electric current to pass through it More salts = stronger current Measured in practical salinity units (psu) Average salinity of seawater = 35 psu
Guestimate How many elements are there in sea salt?
What is the Salt in Saltwater? Seawater contains over 70 elements! Chloride- 55% Sodium- 31% Sulfate- 8% Magnesium- 4% Others- 3% What is table salt composed of? Sodium Chloride
Is the Ocean Mined? Yes! Salt and magnesium are mined from the ocean.
Important Trace Elements Calcium Required for hard shells to form Nitrogen and phosphorus Required for photosynthesis
Too Much Nitrogen = Eutrophication (Algal Blooms) Depending on the type of algae, can be toxic to marine life.
How does salt get into the ocean? Underwater volcanoes release minerals (hydrothermal vents) Erosion of mineral-rich rocks Decomposition of dead marine animals Freezing ice sheets Scientists think that the salt composition of the oceans has been much the same for 200 million years!
How does salt leave the ocean? Plants and animals take up dissolved minerals Minerals precipitate out of solution and settle to the ocean floor
Variations in Salinity Salinity varies from place to place Extreme heat and cold higher salinity due to water evaporation River entry points, areas of heavy rainfall or snow melt lower salinity due to entering freshwater
Water Masses Scientists study water masses (similar to air masses) Salinity and temperature are important for identifying water masses and tracking movements in the ocean NASA s Aquarius mission Feb. 2013 imaged salinity in Earth s oceans for the first time. (3:17) https://www.youtube.com/watch?v=5xqp_b18vmw
Temperature Profile of the Ocean Blank or Notebook Paper
Almost all the energy that heats the ocean comes from the. Because water temperature doesn t change quickly, temperature decreases rapidly with depth.