1. pH and Salts Colligative Properties of Seawater vs. Freshwater Determining Salinity, Temperature, and Depth

2. MenuPreviousNext 6 - 2 Acidity and Alkalinity npH changes with depth because the amount of carbon dioxide tends to vary with depth. nH 2 O + CO 2 --  H 2 CO 3 which is an acid  Shallow depths have less carbon dioxide with a pH around 8.5. because photosynthesis uses CO 2 up  Middle depths have more carbon dioxide and the water is slightly more acidic with a lower pH. with no Photosynthesis to remove the carbon dioxide. The Inorganic Chemistry of Water Chapter 6 Pages 6-21 & 6-22

3. MenuPreviousNext 6 - 3 Acidity and Alkalinity (continued) The Inorganic Chemistry of Water Chapter 6 Pages 6-21 & 6-22 At 3,000 meters (9,843 feet) and deeper, the water becomes more alkaline again. This is because the decay of sinking organic material produces carbon dioxide, and there are no photosynthetic organisms to remove it.

4. MenuPreviousNext 6 - 4 Salts and Salinity nSalinity includes the total quantity of all dissolved inorganic minerals in seawater. nSalinity is expressed in parts per thousand because even very small variations are significant. nThe ocean’s salinity= 35 (‰)which is parts per thousand n(Note: To convert parts per thousand into percent, you divide by 10, so that 35‰ = 35%.) nSodium chloride (rock salt or halite) is the most common and abundant sea salt. The Inorganic Chemistry of Water Chapter 6 Pages 6-9 to 6-11

5. MenuPreviousNext 6 - 5 The Inorganic Chemistry of Water Chapter 6 Pages 6-9 to 6-11

6. MenuPreviousNext 6 - 6 The Principle of Constant Proportions nIn seawater no matter how much the salinity varies, the proportions of several key inorganic elements and compounds do not change. Dissolved Solids in Seawater The Inorganic Chemistry of Water Chapter 6 Page 6-13

7. MenuPreviousNext 6 - 7 The Colligative Properties of Seawater nAbility to conduct an electrical current. A solution that can do this is called an electrolyte.  Decreased heat capacity. Takes less heat to raise the temperature of seawater.  Raised boiling point. Seawater boils at a higher temperature than pure fresh water.  Decreased freezing temperature. Seawater freezes at a lower temperature than fresh water due to increased salinity.  Slowed evaporation. Seawater evaporates more slowly than fresh due to the attraction between ions and water molecules.  Ability to create osmotic pressure. The Inorganic Chemistry of Water Chapter 6 Pages 6-12 & 6-13

8. MenuPreviousNext 6 - 8 Osmotic Pressure in Seawater The Inorganic Chemistry of Water Chapter 6 Pages 6-12 & 6-13

9. MenuPreviousNext 6 - 9 Determining Salinity, Temperature, and Depth nIf you know how much you have of any one seawater chemical, you can figure out the salinity using the principle of constant proportions. nChloride accounts for 55.04% of dissolved solids – determining a sample’s chlorinity is relatively easy. nThe formula for determining salinity is based on the chloride compounds: salinity ‰ = 1.80655 x chlorinity ‰ Sample of seawater is tested at 19.2‰ chlorinity: salinity ‰ = 1.80655 x 19.2‰ salinity ‰ = 34.68‰ The Inorganic Chemistry of Water Chapter 6 Pages 6-13 to 6-16

10. MenuPreviousNext 6 - 10 Determining Salinity, Temperature, and Depth nMost commonly, salinity is determined with a salinometer. This device determines chlorinity and calculates the salinity based on the water’s electrical conductivity. It is accurate. nThe primary tool to measure the properties of seawater is the conductivity, temperature, and depth (CTD) sensor. The CTD profiles temperature and salinity with depth. nAnother less accurate way to determine salinity is with a refractometer. The Inorganic Chemistry of Water Chapter 6 Pages 6-13 to 6-16

11. MenuPreviousNext 6 - 11 Determining Salinity, Temperature, and Depth The Inorganic Chemistry of Water Chapter 6 Pages 6-13 to 6-16 Salinometer CTD Sensor Simple Refractometer