Year 12 Chemistry - Shipwrecks

Minerals in oceans Oceans contain an average of 3.5% (35 g/L) of salts Colder regions (polar waters) contain less and warmer regions (tropical waters) contain more Salts produce a high level of ions is solutions, making them electrolytes, which allows redox reactions to occur. Electrolyte: a substance which when dissolved in a solvent such as water, or when molten, is able to conduct an electric current during electrolysis The percentage of ions in the oceans

Sources of Minerals Salts from the land leaching The Earth has a significant amount of minerals within soils and rocks that are soluble in water. Rain water seeps into the soil and dissolves these minerals, carrying them via waterways to the oceans. This process is known as leaching. The concentration of particular salts depends on the rocks (e.g. limestone will have high concentrations of Ca and carbonate ions).

Sources of Minerals Hydrothermal vents (“black smokers”) Where tectonic plates beneath the ocean meet and are moving apart, molten material comes into contact with sea water. This sea water becomes superheated and dissolves surrounding minerals which rise into the oceans forming hydrothermal vents. Some minerals precipitate when meeting the cold water, but some stay dissolved and are dispersed in the oceans. Source:

Hydrothermal vents Click here to see a videohere

Dissolved Gases in the oceans Many gases are added to seawater from the atmosphere through the constant stirring of the sea surface by wind and waves. The higher the temp/salinity the less the gases will dissolve. Source: Seawater also contains small amounts of dissolved gases. Some of the important atmospheric gases found in seawater include: nitrogen, oxygen, carbon dioxide (in the form of bicarbonate HCO 3 ). Compared to the other atmospheric gases, the amount of carbon dioxide dissolved in saturated seawater is unusually large.

GASES IN AIR AND DISSOLVED IN SEA WATER AT EQUILIBRIUM WITH AIR The percentage of gases in sea water is based on the total gases dissolved in sea water at equilibrium with air. GasChemical SymbolPercentage in Air Percentage in Sea Water NitrogenN OxygenO ArgonAr Carbon DioxideCO NeonNe HeliumHe MethaneCH KryptonKr Carbon MonoxideCO Nitrous OxideN 2 O XenonXe Source:

Dissolved Oxygen Can you explain the oxygen curve above? Answer: O 2 is high at the surface due to mixing with surface air and because of photosynthesis carried out by water plants and phytoplankton. These processes decrease with depth and decomposing material that falls due to gravity, consumes O 2 as it falls (minimum at approx. 1000m). Ocean currents carry O 2 to the depths and as depth increases, temperature decreases and pressure increases. These conditions allow for higher O 2 concentrations