Ocean Water Chemistry Chap 13 – Section 3
Why is ocean water salty? • Undersea volcanoes erupted, ejecting chemicals into the water • Rains eroded land washing chemicals from rocks into the ocean • Over a LONG period of time this produced the salty ocean water
SALINITY • Salinity is a measurement of the total amount of dissolved salts in a sample of water • Average % - ocean water is 3.5% dissolved salts and 96.5% water • Salinity usually measured in parts per thousand 1000 g sample of ocean water 35 parts per thousand 965 grams of water 35 grams of dissolved salts
Composition of Seawater • Sodium chloride is present in the largest amount • In water, it dissolves and the sodium and chloride separate into ions. • Sodium & Chloride ions make up over 80% of the ions in salt water!
Salinity is usually lower at the surface. WHY? Rain, sleet, etc adds fresh water lowering the salinity. Salinity is usually lower near the mouths of rivers. WHY? Rivers dump fresh water into the ocean! Salinity is usually higher near the equator and the poles. WHY? Surface water evaporates in the warming climates leaving salt behind or surface water freezes leaving salt in liquid water.
How does salinity levels affect the water? • It lowers the freezing point of water. Ocean water freezes at -1.9oC instead of 0oC. • Salt water has a higher density than fresh water therefore saltwater has a greater buoyancy. • It “lifts” floating objects higher.
The Dead Sea The Dead Sea is the saltiest body of water in the world – it has the highest salinity. It has a salinity 8.6 times ocean water’s salinity. Salinity is btw 300 – 400 parts per thousand!!
What is used to measure salinity? • HYDROMETER A tube that is calibrated and is put in the water to see how high it floats!
Other Ocean Properties • Temperature: Warm water = lower density; rises Cold water = higher density; sinks As you move away from equator ocean water temp decreases. Temperature decreases with depth. Deeper = colder! • Gases: Dissolved gases in water that organisms must have to live! Oxygen and Carbon Dioxide CO2 is very plentiful in the ocean. O2 is more scarce Amount of dissolved oxygen is affected by temperature! Higher temp = less oxygen Lower temp = more oxygen
Temperature variation in oceans EQUATOR WARMER temps near equator!
Comparison of Salinities • Brine has the highest • Fresh has the lowest • What does ppt stand for?
CHANGES WITH DEPTH • Temperature decreases and pressure increases! In order for scientists to study under water they must use SUBMERSIBLES. They are built to resist pressure.
Lab –Investigating Changes in Density • We are going to make our own hydrometer using a pencil and tacks! • You are going to measure the differences in density of warm and cold water. • You will then measure water samples with different salinities. • Read the lab on pg. 454 of your textbook.