Sodium chloride in seawater

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. 

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. 

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 ... 

Sodium chloride has long been used as a shale stabilizer because of low cost, wide availabiUty, and its presence in many subsurface formations. The inhibitive nature of salt muds increases as the salt content increases from seawater to saturated sodium chloride. In addition to the sodium chloride consumed aimuaHy for drilling fluid, considerable quantities are incorporated while drilling salt zones. This material has been used more for minimizing washouts in salt zones than for stabilizing shales. High salt levels have found appHcation in deep water drilling (7). 

Water is called the universal solvent because of its ability to dissolve at least a little of virtually every substance. Water is a particularly good solvent for substances held together by polar or ionic bonds. Indeed, the most abundant substance dissolved in seawater is an ionic solid, sodium chloride. In comparison, only small amounts of nonpolar substances, such as hydrocarbon oils, will dissolve in water. 

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. 

Figure 2.9 Flux and rejection data for a model seawater solution (3.5 % sodium chloride) in a good quality reverse osmosis membrane (FilmTec Corp. FT 30 membrane) as a function of pressure [10]. The salt flux, in accordance with Equation (2.44), is essentially constant and independent of pressure. The water flux, in accordance with Equation (2.43), increases with pressure, and, at zero flux, meets the pressure axis at the osmotic pressure of seawater 350 psi...

De Bmybn W.J., Saltzman, E.S. (1997) The solubility of methyl bromide in pure water, 35%o sodium chloride and seawater. Marine Chem. 56, 51-57. 

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. 

Sodium chloride can also be obtained from seawater and brine. Brine is similar to seawater, but it contains more dissolved salt. Removing sodium chloride from seawater or brine is easy. All that is needed is to let the water evaporate. The sodium chloride is left behind. It only needs to be separated from other chemicals that were also dissolved in the water. 

Seawater is evaporated by concentrating the seawater in the first evaporation pool transporting to the next evaporation zone, in which calcium sulfate precipitates out and finally crystallizing sodium chloride in a further evaporation zone. The residual brine is rich in potassium and magnesium salts. The salt obtained is too impure to be used in electrolysis. Washing in special units is sufficient to increase the sodium chloride content to > 99%. I m- of seawater yields ca. 23 kg of sodium chloride. 

CE of anions in solutions of high salt content has a number of practical applications. Bromide and nitrate in seawater were detected without any pretreatment or dilution of the samples. Anions in other high-salt samples can also be analyzed directly. Figure 10.8 shows peaks for 10 ppm bromide and 2 ppm nitrate in 0.50 M sodium sulfate. The BGE contained 1.5 pure sodium sulfate. It was also possible to determine both bromide and nitrate in 0.5 M sodium perchlorate by using 1.5 M sodium perchlorate in the BGE. With 1.5 M sodium chloride in the BGE, perchlorate and nitrate coeluted and only bromide could be measured. 

Seawater contains many dissolved substances, mostly dissolved sodium chloride. In Chapter 4, you learned that sodium chloride is an ionic compound. Another ionic compound found dissolved in seawater is magnesium chloride. Some common ionic compounds used in everyday life are potassium chloride, a salt substitute used by people avoiding sodium for health reasons potassium iodide, added to table salt to prevent iodine deficiency and sodium fluoride, added to many toothpastes to strengthen tooth enamel. You will learn how to use the language of chemistry to name and write the formulas of ionic compounds. 

The total volume of seawater is 1.5 X 10 L. Assume that seawater contains 3.1 percent sodium chloride by mass and that its density is 1.03 g/mL. Calculate the total mass of sodium chloride in kilograms and in tons. (1 ton = 2000 lb 1 lb = 453.6 g)... 

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. 

Sodium chloride (table salt) is an essential nutrient for humans and other animals. It is also the major substance dissolved in seawater. Describe a simple method for separating sodium chloride from seawater. 

The apparatus shown in Figure 2.11 could be used, for example, to prepare fresh water from seawater, which can be considered a solution of sodium chloride in water. The seawater to be purified is placed in a round-bottomed distillation flask heated with an electrically powered heating mantle. The seawater is boiled and pure water vapor in the gaseous state flows into the condenser, where it is cooled and condensed back to a purified salt-free product in the receiving flask. When most of the seawater has been evaporated, the distillation flask and its contents are cooled and part of the sodium chloride separates out as crystals that can be removed. 

Perhaps it was in seawater with its chloride miHeu that life began. The element is present in considerable concentrations as sodium chloride in aU cells and body fluids. Even though it does not take part directly in many biochemical reactions, it is important for ionic balance, as it provides the negative charges that neutralize the positive metal cations. 

Sodium Metallurgy Sodium metal is obtained by the electrolysis of molten, or fused, sodium chloride. Sodium chloride is mined from huge underground deposits. The other source of sodium chloride is seawater, which is a solution of many dissolved substances, but sodium chloride is the principal one. Sodium chloride melts at 801°C, but commercial electrolysis employs a mixture of NaCl and CaCl2, which melts at 580°C. We discussed the electrolysis in some detail in Section 20.9. ... 

Sodium chloride, gypsum, and potassinm salts are all important minerals that are recovered as evaporites remaining from the evaporation of seawater and from brines pumped from below the ground. Sodium chloride in the form of mineral halite is used as a raw material for the production of industrially important sodium, chlorine, and their compounds. It is used directly to melt ice on roads, in foods, and in other applications. Potassium salts are, of course, essential ingredients of fertilizers and have some industrial applications as well. Gypsum, hydrated calcium sulfate, is used to make plaster and wallboard and is an ingredient in the manufacture of portland cement. 

The apparatus shovm in Figure 2.11 could be used, for example, to prepare fresh water from seawater, which can be considered a solution of sodium chloride in... 

The conversion pathway is g sodium chloride g seawater —> mL seawater L seawater. To convert from g sodium chloride to g seawater, we need the conversion factor in expression (1.3), with g seawater in the numerator and g sodium chloride in the denominator. To convert from g seawater to mL seawater, we use the reciprocal of the density of seawater as the conversion factor. To make the final conversion, from mL seawater to L of seawater, we use the fact that 1L = 1000 mL. 

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