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Seawater, or sea water, is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% (35 g/L, 35 ppt, 600 mM). This means that every kilogram (roughly one liter by volume) of seawater has approximately 35 grams (1.2 oz) of dissolved salts (predominantly sodium ( Na +
The resulting 'Knudsen salinities' are expressed in units of parts per thousand (ppt or ‰). The use of electrical conductivity measurements to estimate the ionic content of seawater led to the development of the scale called the practical salinity scale 1978 (PSS-78). [9] [10] Salinities measured using PSS-78 do not have units.
A change in pH by 0.1 represents a 26% increase in hydrogen ion concentration in the world's oceans (the pH scale is logarithmic, so a change of one in pH units is equivalent to a tenfold change in hydrogen ion concentration). Sea-surface pH and carbonate saturation states vary depending on ocean depth and location.
Besides the well-known Pitzer-like equations, there is a simple and easy-to-use semi-empirical model, which is called the three-characteristic-parameter correlation (TCPC) model. It was first proposed by Lin et al. [ 22 ] It is a combination of the Pitzer long-range interaction and short-range solvation effect:
Deep sea water column The (oceanic) water column is a concept used in oceanography to describe the physical (temperature, salinity , light penetration) and chemical ( pH , dissolved oxygen , nutrient salts) characteristics of seawater at different depths for a defined geographical point.
At 20 °C (68 °F) one liter of water can dissolve about 357 grams of salt, a concentration of 26.3 percent by weight (% w/w). At 100 °C (212 °F) (the boiling temperature of pure water), the amount of salt that can be dissolved in one liter of water increases to about 391 grams, a concentration of 28.1% w/w.
In the technical terms of physical chemistry, the minimum freezing point of a water-salt mixture is −21.12 °C (−6.02 °F) for 23.31 wt% of salt. Freezing near this concentration is however so slow that the eutectic point of −22.4 °C (−8.3 °F) can be reached with about 25 wt% of salt. [13]
The particular substance sampled may be specified using a subscript, e.g., the amount of sodium chloride (NaCl) would be denoted as n NaCl. The unit of amount of substance in the International System of Units is the mole (symbol: mol), a base unit. [1] Since 2019, the value of the Avogadro constant N A is defined to be exactly 6.022 140 76 × ...