Chlorides in seawater

Write the chemical equation for (a) the industrial preparation of magnesium metal from the magnesium chloride in seawater (b) the action of water on calcium metal. 

The large amount of sodium chloride in seawater samples causes nonspecific absorption [366-370], which can only be partially compensated by background correction. In addition the seawater matrix may give rise to chemical as well as physical interferences related to the complex physico-chemical phenomena [371-373] associated with vaporization of metals and of the matrix itself. 

The Bellar et al. [219] purge and trap method has been applied to the determination of vinyl chloride in seawater. Using the Hall electrolytic conductivity detector, no response was obtained for the acetone used to prepare the vinyl chloride standard solution. 

Stoeppler and Matthes [44] have made a detailed study of the storage behaviour of methylmercury and mercuric chloride in seawater. They recommended that samples spiked with inorganic and/or methylmercury chloride be stored in carefully cleaned glass containers acidified with hydrochloric acid to pH 2.5. Brown glass bottles were preferred. Storage of methylmercury chloride should not exceed 10 days. 

May et al. [45] used radiochemical studies to ascertain the behaviour of methylmercury chloride and mercuric chloride in seawater under different storage conditions. The application of 203Hg unambiguously revealed that the loss of mercury observed upon storage of unacidified seawater samples in polyethylene bottles was due to adsorption and to the diffusion of metallic Hg (Hg°) through the container wall. 

Hydrolyzes in water forming methyl alcohol and hydriodic acid. The estimated half-life in water at 25 °C and pH 7 is 110 d (Mabey and Mill, 1978). At 70 °C, the hydrolysis rate was determined to be 3.2 X 10 Vsec which is equivalent to a half-life of 6 h. (Glows and Wren, 2003). May react with chlorides in seawater to form methyl chloride (Zafiriou, 1975). 

Chlorine is the 20th most abundant element on the Earth. It is not found as a free element (atoms) except as a diatomic gas escaping from very hot active volcanoes. It has been known for thousands of years as rock salt (hahte). It is also found in sylvite and carnalhte and as a chloride in seawater. In nature, it is mostly found in dissolved salts in seawater and deposits in salt mines. Its best-known compound is sodium chloride (NaCl), which is common table salt. Chlorine is important for the chemical industry. Numerically, it is the 12th most produced chemical in the United States and ranks ninth in volume of chemicals produced in the United States. 

Chlorine does not occur in the elemental state because of its high reactivity. In nature the element occurs mainly as sodium chloride in seawater. Its abundance in seawater is 1.9% by weight. It also exists as chloride in many rocks and minerals such as camaUite (KMgCls 6H2O) and sylvite (KCl). 

When a nonvolatile solute is present in a solution (such as the sodium chloride in seawater), the boiling point of the solvent is increased. This increase is called boiling-point elevation. The origin of boiling-point elevation is the effect of the solute on the entropy of the solvent. 

Seawater contains about 3.5% salts, in which the content of sodium chloride is about 80%. The concentration of dissolved salts as well as temperature and pressure influence the physical properties of seawater. The total salt concentration is usually called salinity . Salinity is generally measured by the electrical conductivity or determination of chloride content. At present, salinity(S) is defined as S = 1.80655 Cl (Cl is the concentration of chloride in seawater) [5]. Dissolved oxygen and silica are usually measured as additional parameters to characterize seawater. The concentrations of nitrogen and phosphorus are the indices of nutrients and measure the fertility and production of the oceans. 

Chlorine occurs in Nature mainly as sodium chloride in seawater and in various inland salt lakes, and as solid deposits originating presumably from the prehistoric evaporation of salt lakes. Chlorine is prepared industrially mainly by electrolysis of brine ... 

Figure 2 makes it clear that —log y falls slowly as hydrochloric acid replaces a part of the sodium chloride in seawater I. The linear variation is in accord with Hamed s rule, and the magnitude of the drop is a measure of —log ynci referred to the new standard state. The behavioral similarity between seawater I and 0.66M sodium chloride is illustrated by the fact that the values of log ynci for these two solvents at Hci = 0.06 mole/kg are —0.001 and —0.002, respectively. 

A 1 liter sample of seawater contains 29.25 g of sodium chloride. What is the molar concentration of sodium chloride in seawater sample ... 

The minerals from which the metals are extracted, existed for millions of years in the earth s crust and are the most stable form of the metal. A considerable amount of energy is required to convert this mineral into the metal. Once this pure metal comes into contact with the natural environment such as sea-water or soils, the metal slowly converts back to its original starting material. Iron, for example, is obtained from the mineral, haematite, an oxide of iron. Once the pure iron comes into contact with water and air (oxygen), it slowly converts back to the oxide. This is called corrosion and the product is familiar to everyone as red rust. Nearly all metals will corrode in natural environments although the rates of corrosion will vary from metal to metal and alloy to alloy. In addition, the rates of corrosion will vary from one natural environment to another. Iron will corrode at approximately 50 pun per year in freshwater but at 120 pm per year in seawater. The reason for this is due to the difference in chemical composition between freshwater and seawater. The latter contains salt (sodium chloride) and this is very deleterious to the corrosion behaviour of the metal. Silver artefacts may be excavated after several hundred years buried in soils with only minimal amounts of corrosion. Those recovered from marine sites after a similar period of burial, have completely corroded and have reverted back to 100% mineral. This is entirely due to the presence of chlorides in seawater. 

SO4/CI) designates the molal concentration ratio of sulfate to chloride. In seawater this ratio is 0.0516. 

Although it is probable that methyl chloride in seawater arises from biological processes, the route to its production is still obscure. Zafiriou... 

Magnesium has a high chemical reactivity, and for this reason it is never found in nature in its free state but rather in compounds—as chloride in seawater and in salt deposits such as carnallite (MgCl2 KCl - 6H2O) and as carbonates in the ores dolomite (MgCOs CaCOs) and magnesite (MgCOs), etc. 

Reinforced concrete structures exposed to marine environments suffer premature corrosion-induced deterioration by chloride in seawater. Corrosion is typically found in piers and docks, bulkheads and retaining walls, mooring structures and navigational aids. 

The determination by means of nitration of an organic compound such as 2,6-xylenol Hartley and Asai, 1963) is subject to interference from large amounts of chloride in seawater and is not sensitive enough. 

Some organic compounds form coloured products if they are oxidized by nitrate ions in acid solution. Examples are brucine (Jenkins and Medsker, 1964), diphenylbenzidine Atkins, 1954), reduced strychnidine Dal Pont, 1962), diphenylamine Isaeva, 1958) and resorcinol Costa, 1951). However, no reliable trouble-free method has been developed based on this technique. Another spectrophotometric method based on the formation of nitrosyl chloride in seawater containing 50 % concentrated sulphuric acid has been developed by Armstrong (1963), but this method cannot be recommended because of the difficulties connected with handling concentrated sulphuric acid solutions at sea, and because it is relatively insensitive. 

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