The Chemistry of the Earth CHAPTER 19 The Chemistry of the Earth 19.2 Chemistry of the Oceans

Why is Earth sometimes called the “Blue Planet”?

Why is Earth sometimes called the “Blue Planet”? 70.9% of Earth’s surface is covered with water

Distribution of water 97.0% H2O is in the oceans 2.3% ice caps and glaciers 0.7% ground water, lakes, rivers…

Importance of water Water acts as a solvent Many chemical reactions, including those in living systems, can only happen in an aqueous solution Water in acid-base reactions Water is amphoteric; it can accept a proton from an acid, or donate a proton to a base Water in oxidation-reduction reactions The salt dissolved in ocean water makes it conductive, and electrons transfer reactions can occur

Chemicals in ocean water We know we should not drink ocean water because its salt content would make us more thirsty. Ocean water contains 3.5% salt ions, mostly Cl– and Na+. salinity: the concentration of salt in water.

Chemicals in ocean water

The water cycle Except for photosynthesis, the water cycle is a physical process. The water molecule is not chemically changed.

transpiration: the release of water from the leaves of plants as they carry out photosynthesis.

Ocean currents Water absorbs energy from the sun and distributes it. Warm water has higher kinetic energy, and water molecules are more spread out, leading to lower density.

Ocean currents Warm water cools off as it gets closer to the poles. Cold water has lower kinetic energy, and water molecules are less spread out, leading to higher density.

Ocean currents Cold water is denser and sinks to the bottom. Salt does not freeze so the salt concentration in the remaining water increases.

This overall movement creates a current Ocean currents Some of the warm water also evaporates, bringing precipitation on land. As cold water sinks, more water is pulled in to replace it. This overall movement creates a current

Carbon in water One of the gases dissolved in water is carbon dioxide, CO2 CO2(g) + H2O(l) H2CO3(aq) carbonic acid In water, the formation of carbonate ions is favored H2CO3(aq) + H2O(l) H+(aq) + CO3–(aq) carbonate ion

The carbon cycle Unlike the water cycle, the carbon cycle is a chemical process. Carbon can be found in CO2 in air, H2CO3 in water, and C6H12O6 in plants

The carbon cycle is a chemical process. Water is crucial - as a solvent - in acid-base chemistry - in redox reactions The water cycle is mainly a physical process (except for photosynthesis). The carbon cycle is a chemical process. Water properties in function of temperature create currents that can move massive amounts of ocean water