Oxygen dissolved in sea-water

Oxygen, dissolved in sea-water in equilibrium with a normal . atmosphiere 76C mm) of iair saiurated with water vapour... 

Note the table gives the quantity of oxygen dissolved in sea-water at dirferent temperatures and chlorinities when in equilibrium with a normal atmosphere saturated with water vapour, li thus represents the condition approached by the surface water when biological activity is not excessive. 

In parallel to reaction 3.6, oxygen dissolved in sea water is reduced to peroxide according to Eq. (4.13). The challenge is to avoid a precipitation of LiOH and Mg(OH)2 both at the cathode and GCE. Mg(OH)2 is formed by the reaction of Mg " ions that are present in sea water in high concentration, with hydroxyl ions produced by Eq. (4.22). 

The procedure used was to determine the concentration of dissolved oxygen (02) with an 02-electrode63. A (linear) calibration curve was prepared of current (due to the response of the 02-electrode) vs. oxygen concentration in sea water ranging from fully deaerated to saturation at an 02 pressure of one atmosphere. 

The carbon cycle in seas involves the assimilation of carbon dioxide dissolved in sea water by the phytoplankton with a simultaneous oxygen release. Zooplankton and fish use this oxygen for the respiration. During the organic matter decomposition, CO2 is supplied into the atmosphere. On land, the exchange of carbon dioxide with the atmosphere is accomplished by respiration, photosynthesis and by the combustion of fossil fuels. 

Dissolved oxygen is a very important factor in the corrosion of metals immersed in sea water. Because of its biological significance, a vast amount... 

Palladium is considerably less resistant to anodic corrosion than platinum, though it may be used for evolution of oxygen from alkaline solutions. It is attacked rapidly when used as an anode in sea-water, and dissolves quantitatively in acid chloride solutions. 

Paints used for protecting the bottoms of ships encounter conditions not met by structural steelwork. The corrosion of steel immersed in sea-water with an ample supply of dissolved oxygen proceeds by an electrochemical mechanism whereby excess hydroxyl ions are formed at the cathodic areas. Consequently, paints for use on steel immersed in sea-water (pH 8-0-8-2) must resist alkaline conditions, i.e. media such as linseed oil which are readily saponified must not be used. In addition, the paint films should have a high electrical resistance to impede the flow of corrosion currents between the metal and the water. Paints used on structural steelwork ashore do not meet these requirements. It should be particularly noted that the well-known structural steel priming paint, i.e. red lead in linseed oil, is not suitable for use on ships bottoms. Conventional protective paints are based on phenolic media, pitches and bitumens, but in recent years high performance paints based on the newer types of non-saponifiable resins such as epoxies. 

Tsunogai S. and Tanaka N. (1980) Flux of oxygen across the air-sea interface as determined by the analysis of dissolved components in sea-water. Geochem. J. 14, 227 -234. 

Soluble salts—halite (NaCl) and gypsum (CaSC>4 2H2O), as well as sulfides (pyrite, FeS2) in soils reclaimed from seas or swamps. These minerals readily dissolve in percolating water or, in the case of the sulfides, are readily attacked by oxygen. Saline and sodic ( alkali ) soils are examples of this category. 

The reaction of dissolved Fe with oxygen is known to be fast and its rate was determined in sea-water by Millero et al. (1987) ... 

Hetman (21) has used this type of instrument for the determination of cyanide ions in water. By the use of an anodic voltage sweep he was able to determine as little as 0.05 /xg./ml. of cyanide in a sodium hydroxide supporting electrolyte. Whitnack (56) has used this technique to determine copper, lead, zinc, and manganese at the 0.05 /xg./ml. level in sea water. He also used it for continuous monitoring of chloride and dissolved oxygen. 

In solution, a dissolved trace gas in equilibrium with the atmosphere would have the same partial pressure as the gas in the air. Its absolute concentration in terms of molecules or mass per unit volume of water depends on its solubility. Gas solubility varies over many orders of magnitude depending on the affinity of water for the gas molecules and the volatility of the gas. Gases range widely in their solubility in sea water, from the permanent gases like nitrogen (N2), oxygen (O2), nitrous oxide (N2O) and methane (CH4) that have a low solubility in sea... 

The chemical components of calcium carbonate — dissolved calcium ions and carbon dioxide — are widely distributed. Calcium is the fifth most common element in the earth s crust (after oxygen, silicon, aluminium and iron). It was extracted from early igneous rocks by the combined effects of erosion by the weather and corrosion by acidic gases (oxides of sulfur, oxides of nitrogen and carbon dioxide dissolved in rain water). Carbon dioxide makes up about 0.03 % by volume of the earth s atmosphere and is dissolved in both fresh and sea water. Combination of dissolved calcium ions and carbon dioxide resulted in the sedimentary deposition of calcium carbonate, which was subsequently converted into limestone rock. Early limestones (Precambrian — Table 2.1) are believed to have been deposited as precipitates of CaCOa, and/or as a result of the biochemical activity of very simple organisms, such as bacteria. 

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