Salt Water

Properties of Salt Water  Salinity is the amount of dissolved salts in water  The salinity of the oceans averages 35 ppt (parts per thousand)  Fresh water averages 10 ppt  There are some variations in salinity due to differences in: the rates of evaporation, precipitation, and run-off

Differences in Salinity  The salinity of the Red Sea is 41ppt and the salinity of the Dead Sea is nearly 300 ppt  Table salt (NaCl) accounts for 87% of the salinity of sea water  Sea water contains at least a trace amount of most elements found in the Earth’s crust

Red Sea

Dead Sea

Salinity and Freezing  Salinity affects the freezing point of water  When ice forms in seawater the salt is extruded from the ice, leaving a more salty water beneath the ice.  Seawater therefore has no fixed freezing point

Salinity and Density  Seawater is more dense than freshwater, so freshwater floats on seawater  An increase in salinity increases the density  A hydrometer is an instrument used to measure the buoyancy of a liquid by comparing its buoyancy to that of pure water

 It can be used to measure density  If the liquid is more dense than water, the hydrometer will float higher  If the liquid is less dense than water, they hydrometer will sink more

 Major constituents of seawater at 34.32% salinity:  Chloride ions  Sodium ions  Sulfate  Magnesium  Calcium  potassium  Bicarbonate  This is a chlorine atom

 Chloride and sodium give the ocean its salty taste  Molluscs use the calcium to make their shells  Crustaceans use calcium salts to build their bodies  Diatoms use silica to form their shells

 Snails secrete lead  Sponges remove iodine from the sea

How salty is the ocean?  Maybe 50 million billion tons of dissolved solids  If the salt was removed, it would cover the Earth’s surface, 500ft thick  When 1 cubic foot of ocean water evaporates, it leaves 2.2 pounds of salt  When 1 cubic foot of Lake Michigan (fresh water) is evaporated, it leaves 0.01 pounds of salt  So, sea water is 200x saltier than fresh water

Origin of the Sea  “ocean” and “sea” are used in the same context here  It is believed to be 500 million years old, based on fossil evidence  Scientists are unsure of what has formed the ocean, but believe that the atmosphere and the oceans have evolved over time from “degassing” of the Earth’s interior

 So, water vapour and other gases left the interior, went to form clouds  The Earth’s surface cooled  Rain began to fall for centuries  Rain drained into hollows in the Earth’s surface and formed an ocean  Gravity prevented it from leaving  Salts come from the breaking down of materials of the Earth’s crust

 Salt enters the sea from rivers and streams, and then is deposited on the ocean floor  The Sun’s heat vaporized pure water and leaves the salt behind