Links and Connections WITHIN CHEMISTRY 1. See module on Solubility and Precipitation. 2. The volume of the earth’s oceans is 1.4 x 10 21 L, with a concentration of sodium chloride of 31.3 g per kg of seawater. Total number of moles of sodium chloride in the ocean is 7.5 x 10 20 , which is equivalent to 4.4 x 10 22 g or 4.9 x 10 16 tons. BETWEEN CHEMISTRY AND OTHER DISCIPLINES Biology (saline solutions and solution concentrations) Geology Economics Physics (physical separations) Oceanography
TO THE CONTEMPORARY WORLD Personal 1. Kelp (seaweed) is harvested to provide many products. The most important of these is probably algin, or sodium alginate, a polysaccharide with gelling properties. It finds uses in ice cream and soft drinks. 2. The similarities between seawater and blood: Both composed of mostly water. Both have similar densities. Both contain similar percentages of dissolved salts. Both have similar pH values. Both are slightly basic. Community Obviously, teachers in communities on or near an ocean (or the Great Salt Lake) can plan many field trips and take advantage of experts in the area. Teachers in inland cities can use museums and museum directors as resources. Marine biologists and chemists are hired by aquariums (Seaworld and Disney Epcot Center, for example) to maintain balanced ecosystems in display tanks. Societal (Science/Technology/Society; Current Events) 1. Increasingly, the desalinization of seawater looks attractive as a source of fresh water for populations of arid regions. 2. Sea salts are farmed in many areas by drawing the seawater into evaporating ponds. 3. The sea is a source for many very important chemical separations. It is the largest source of Br salts, which are used to make Br 2 . 4. A discussion of some methods of desalination that are currently used: Distillation. In a closed system, evaporation can remove salt from seawater. Upon condensation this fresh water can be isolated from the seawater and collected. Freezing. Because salt interferes with the hydrogen bonding that occurs as water freezes, water will crystallize first where the hydrogen bonding is not inhibited. Therefore, as ice freezes it excludes the salt from the crystal, effectively purifying itself. Reverse osmosis. A semipermeable membrane (a membrane permeable to H 2 O molecules but not to ions or larger molecules) can separate fresh water from seawater. The fresh water, by osmosis, passes into the seawater and dilutes it. The level on the seawater side rises since more H 2 O molecules enter this side than leave. In order to force more H 2 O molecules back into the fresh water side an external force in excess of the osmotic pressure of normal seawater (24.8 atm) is exerted on the seawater side. More fresh water is forced back into the fresh water side than diffused into the seawater. The net result: production of fresh water. Electrodialysis. Very similar to reverse osmosis. A semipermeable membrane selectively isolates the salt from the fresh water. An electrical potential difference speeds the process by attracting the ions. 5. Hydrocarbons in the form of oil and natural gas are being produced from wells on the continental shelves in many areas of the world. Some of the issues raised by such drilling: The size of the oil reservoir. Active earthquake faults. Prevailing winds and currents in the area of a drilling platform. Ecological, social, and economic impacts of drilling activities on the community. Impact of drilling with current oceanic resources such as fishing and recreation. 6. Manganese nodules on the ocean floor contain large amounts of iron and manganese. 7. Phosphate compounds have accumulated on submarine terraces on many continental shelves. 8. Potential gold and diamond deposits lie at the mouths of large rivers. 9. Muds near hot springs on the ocean ridges are rich in metallic minerals. 10. Energy can be derived from the sea by tides, waves, and thermal differences. 11. Major and minor ions in seawater are present in living systems in the same relative concentrations. Does this give any credence to the hypothesis that life originated in the oceans?
Return to table of contents
