Standard Sea Water

The saltiness of the ocean is defined in terms of salinity. In theory, this term is meant to represent the total number of grams of dissolved inorganic ions present in a kilogram of seawater. In practice, salinity is determined by measuring the conductivity of a sample and by calibration through empirical relationships to the International Association of Physical Sciences of the Ocean (IAPSO) Standard Sea Water. With this approach, salinity can be measured with a precision of at least 0.001 parts per thousand. This is fortunate, considering that 75% of all of the water in the ocean falls neatly between a salinity of 34 and 35. Obviously, these high-precision measurements are required to observe the small salinity variations in the ocean. 

The accuracy of the inductively-coupled plasma procedure was assessed by analysing waters of known sulfate composition, and by comparing measured sulfate values for a wide range of samples with those obtained for the same waters by an automated spectrophotometric procedure. Good agreement is obtained between the derived sulfate measurements and the normal values for International Standard Sea Water and an EPA Quality Control Standard. 

Early scientists recognized that standards were needed to determine reliable values of the chlorinity and salinity of seawater. The IAPSO Standard Sea Water Service (originally based in Copenhagen) collected and distributed seawater from the North Atlantic with a known, measured chlorinity. This sample was supplied to oceanographers to standardize the AgNOg solutions used to determine chlorinity in various laboratories. 

By the salinity of sea water is understood the number of grams of total salts in 1000 grams of the water. This may be determined gravimetrically or volumetrieally, the latter method being the most usual, the chlorine being determined, and from it the total salts calculated. This method of course implies suitable laboratory facilities, and if these arc not available the water must be stored until such time as it can be tested. To obviate this difficulty attempts have been made to determine salinity by electric conductivity measurements. By employing a standard sea water and comparing its conductivity with that of the unknown samples, it is claimed that very accurate results are easily obtained at sea or under conditions entire unsuitable for ordinary laboratory work.1... 

Rusby J. S. M. (1967) Measurements of the refractive index of seawater relative to Copenhagen Standard Sea Water. Deep-Sea Res. 14, 427-439. 

On the other hand, if HoO is available in the environment, then the S02 could for example, be converted to acid. But the acid would not be inert, unless dilute. The extent to which it could be diluted would depend upon the amount of H20 in "the relevant system". If the plant is near to the sea, then the concentration of sulfate ions in the sea would dictate the dead state configuration of the sulfur (i.e., the extent of dilution of SO4) see (14) for the listing of available energy values of various elements relative to standard sea water. 

Normal sea water as prepared by the Hydrographic Laboratories of Copenhagen is used whenever a standard sea water is designated. It is slightly more concentrated than other standard sea waters, having a total solids concentration of 35,175 p.p.m. Calcium is 408 p.p.m. magnesium 1298 sulfate 2702 and bicarbonate 142 p.p.m. 

Supply of Sea Water. Sea water was collected from Port Phillip Bay at Frankston, Victoria, some 30 miles from Melbourne, the nearest point to the laboratories at which clean sea water of salinity approximating that of standard sea water (1) could be regularly obtained. The water was transported in 3000-gallon batches by road tanker and delivered into two large rubber-lined tanks at the laboratories. Analyses of the batches over a period of two years gave the results reported in Table I. 

In a few tests a white crystalline Mg(OH)2 scale has been produced, which remains on the tube surface as an attached layer when dry. It is thought that the presence of suitable crystal nuclei in the feed water may account for this result. In tests on one batch of sea water a scale containing approximately 30% CaCOs [remainder largely Mg(OH)2] was produced. Analysis of this batch of sea water showed only minor deviations from standard sea water for the major constituents and no explanation can be offered for this unusual result. 

Electrical resistivities can be measured on split cores by a half-automated logging system (Berg-mann 1996). It measures the resistivity (R ) and temperature (T) by a small probe which is manually inserted into the upper few millimeters of the sediment. The resistivity (R, ) of the interstitial pore water is simultaneously calculated from a calibration curve which defines the temperature-conductivity relation of standard sea water (35%o salinity) by a fourth power law (Siedler and Peters 1986). 

In standard sea water of 35%o salinity density increases by maximum 0.3-10 g cm per °C (Siedler and Peters 1986), i.e. by less than 0.1% per °C. Hence, temperature corrections can usually be neglected. 

The coefficients (c ) to (c ) depend on the geometry of the probe and are determined by a least square fit to the calibration measurements in standard sea water. 

For long-term storage of seawater, the special glass ampoules used by the Standard Sea Water Service should be employed. Seawater sealed in this type of resistant glass has been found to remain unchanged with respect to sample composition, electrical conductivity and density over a period of several years (see also Chapters 3 and 11). 

To preserve continuity with the previous 1%9 definition, the reference KQ solution has a mass fraction of 32.4356 x 10 of KQ, to have the same conductivity as a standard seawater with S=35 (Cl=19.3739%o in the 1969 definition, see Eq. (3-2)). Equation (3-4) is valid for a practical salinity S from 2 to 42. For 15= , the practical salinity is 5=35. As the coefficients in Eq. (3-4) were determined by comparison of diluted and evaporated fractions of standard seawater with the KO solution, a standard sea water with known K15 value may replace the KCl solution as a reference. This is the general practice for preparing standard seawater. 

These considerations, however, do not apply to aqneous solutions beyond the above-stated limits of pH and concentrations and to nonaqueons and mixed aqueous-nonaqueous solutions, for which the nominal hydrogen ion activity, that is, the pH, is required. Sea water is one example of aqueous solutions for which special treatment is needed and highly saline brines is another one. Standard sea water of salinity 0.35% has an ionic strength of about 0.7 m and at 25°C has, because of this, pH=pH(dilute aqueous solu-tions)+0.076 as shown by Bates [12], provided that the cell is standardized with the same electrodes against the standard buffer used in dilute aqueous solutions described above. 

Evaluate the chlorosity (F,) of the primary standard sea water, Eau de Mer Normale, from the equation... 

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