Potassium in seawater

Potentiometric titration has been applied to the determination of potassium in seawater [532-534], Torbjoern and Jaguer [533-544] used a potassium selective valinomycin electrode and a computerised semiautomatic titrator. Samples were titrated with standard additions of aqueous potassium so that the potassium to sodium ion ratio increased on addition of the titrant, and the contribution from sodium ions to the membrane potential could be neglected. The initial concentration of potassium ions was then derived by the extrapolation procedure of Gran. 

Polarography has also been applied to the determination of potassium in seawater [535]. The sample (1 ml) is heated to 70 °C and treated with 0.1 M sodium tetraphenylborate (1 ml). The precipitated potassium tetraphenylborate is filtered off, washed with 1% acetic acid, and dissolved in 5 ml acetone. This solution is treated with 3 ml 0.1 M thallium nitrate and 1.25 ml 2M sodium hydroxide, and the precipitate of thallium tetraphenylborate is filtered off. The filtrate is made up to 25 ml, and after de-aeration with nitrogen, unconsumed thallium is determined polarographically. There is no interference from 60 mg sodium, 0.2 mg calcium or magnesium, 20 pg barium, or 2.5 pg strontium. Standard eviations at concentrations of 375, 750, and 1125 pg potassium per ml were 26.4, 26.9, and 30.5, respectively. Results agreed with those obtained by flame photometry. 

Therefore, iodine occurs in nature as sodium iodate, NaI03 Fluorine occurs as cryolite, Na2AlF6 and fluorspar, CaF2 whereas chlorine and bromine both occur as chlorides and bromides of sodium and potassium in seawater. Seawater contains roughly... 

The overall tendency in these interactions between fluids at different temperatures and basaltic material is the oxidation of iron and the concentration of potassium. The relatively low concentration of potassium in seawater is surely, in large part, due to these interactions. 

In addition to the hematite precipitation - acid regeneration chemistry, sodium and potassium in seawater react with aluminum in solution to form alunite, resulting in low net extraction. Alunite precipitation also regenerates acid, helping to minimize acid consumption, analogous to jarosite precipitation in atmospheric leaching. Sodium alunite precipitation, as shown in equation 9, is an analogue of jarosite precipitation in equation 3. 

Chlorine. Chlorine, the material used to make PVC, is the 20th most common element on earth, found virtually everywhere, in rocks, oceans, plants, animals, and human bodies. It is also essential to human life. Eree chlorine is produced geothermally within the earth, and occasionally finds its way to the earth s surface in its elemental state. More usually, however, it reacts with water vapor to form hydrochloric acid. Hydrochloric acid reacts quickly with other elements and compounds, forming stable compounds (usually chloride) such as sodium chloride (common salt), magnesium chloride, and potassium chloride, all found in large quantities in seawater. 

Table 8 5 shows that each of the four common s-block ions is abundant not only in seawater but also in body fluids, where these ions play essential biochemical roles. Sodium is the most abundant cation in fluids that are outside of cells, and proper functioning of body cells requires that sodium concentrations be maintained within a narrow range. One of the main functions of the kidneys is to control the excretion of sodium. Whereas sodium cations are abundant in the fluids outside of cells, potassium cations are the most abundant ions in the fluids inside cells. The difference in ion concentration across cell walls is responsible for the generation of nerve impulses that drive muscle contraction. If the difference in potassium ion concentration across cell walls deteriorates, muscular activity, including the regular muscle contractions of the heart, can be seriously disrupted. 

Schnepfe [83] has described yet another procedure for the determination of iodate and total iodine in seawater. To determine total iodine 1 ml of 1% aqueous sulfamic acid is added to 10 ml seawater which, if necessary, is filtered and then adjusted to a pH of less than 2.0. After 15 min, 1 ml sodium hydroxide (0.1 M) and 0.5 ml potassium permanganate (0.1M) are added and the mixture heated on a steam bath for one hour. The cooled solution is filtered and the residue washed. The filtrate and washings are diluted to 16 ml and 1ml of a phosphate solution (0.25 M) added (containing 0.3 xg iodine as iodate per ml) at 0 °C. Then 0.7 ml ferrous chloride (0.1 M) in 0.2% v/v sulfuric acid, 5 ml aqueous sulfuric acid (10%) - phosphoric acid (1 1) are added at 0 °C followed by 2 ml starch-cadmium iodide reagent. The solution is diluted to 25 ml and after 10-15 min the extinction of the starch-iodine complex is measured in a -5 cm cell. To determine iodate the same procedure is followed as is described previously except that the oxidation stage with sodium hydroxide - potassium permanganate is omitted and only 0.2 ml ferrous chloride solution is added. A potassium iodate standard was used in both methods. 

Wong [8] found that the determination of residual chlorine in seawater by the amperometic titrimetic method, potassium iodide must be added to the sample before the addition of the pH 4 buffer, and the addition of these two reagents should not be more than a minute apart. Serious analytical error may arise if the order of addition of the reagents is reversed. There is no evidence suggesting the formation of iodate by the reaction between hypobromite and iodide. Concentrations of residual chlorine below 1 mg/1 iodate, which occurs naturally in seawater, causes serious analytical uncertainties. 

In another spectrophotometric procedure Motomizu [224] adds to the sample (2 litres) 40% (w/v) sodium citrate dihydrate solution (10 ml) and a 0.2% solution of 2-ethylamino-5-nitrosophenol in 0.01 M hydrochloric acid (20 ml). After 30 min, add 10% aqueous EDTA (10 ml) and 1,2-dichloroethane (20 ml), mechanically shake the mixture for 10 minutes, separate the organic phase and wash it successively with hydrochloric acid (1 2) (3 x 5 ml), potassium hydroxide (5 ml), and hydrochloric acid (1 2) (5 ml). Filter, and measure the extinction at 462 nm in a 50 mm cell. Determine the reagent blank by adding EDTA solution before the citrate solution. The sample is either set aside for about 1 day before analysis (the organic extract should then be centrifuged), or preferably it is passed through a 0.45 xm membrane-filter. The optimum pH range for samples is 5.5 - 7.5. From 0.07 to 0.12 p,g/l of cobalt was determined there is no interference from species commonly present in seawater. 

In a method described by Kiriyama and Kuroda [500], molybdenum is sorbed strongly on Amberlite CG 400 (Cl form) at pH 3 from seawater containing ascorbic acid, and is easily eluted with 6 M nitric acid. Molybdenum in the effluent can be determined spectrophotometrically with potassium thiocyanate and stannous chloride. The combined method allows selective and sensitive determination of traces of molybdenum in seawater. The precision of the method is 2% at a molybdenum level of 10 xg/l. To evaluate the feasibility of this method, Kiriyama and Kuroda [500] spiked a known amount of molybdenum and analysed it by this procedure. The recoveries for 4 to 8 xg molybdenum added to 500 or 1000 ml samples were between 90 and 100%. 

Marquis and Lebel [534] precipitated potassium from seawater or marine sediment pore water using sodium tetraphenylborate, after first removing halogen ions with silver nitrate. Excess tetraphenylborate was then determined by silver nitrate titration using a silver electrode for endpoint detection. The content of potassium in the sample was obtained from the difference between the amount of tetraphenyl boron measured and the amount initially added. 

Yamamoto et al. [60] determined picogram quantities of methyl mercury and total mercury in seawater by gold amalgamation and atomic absorption spectrometry. Methyl mercury was extracted with benzene and concentrated by a succession of three partitions between benzene and cysteine solution. Total mercury was extracted by wet combustion of the sample with sulfuric acid and potassium permanganate. The proportion of methyl mercury to total mercury in the coastal seawater sampled was around 1%. 

Schnepfe [4] has described a method for the determination of total iodine and iodate in seawater. One per cent aqueous sulfamic acid (1 ml) is added to seawater (10 ml), then it is filtered, if necessary, and the pH adjusted to 2. After 15 min, 1 ml 0.1 M sodium hydroxide and 0.5 ml 0.1 M potassium permanganate are added and the steam bath heated for 1 h. The cooled solution is filtered, the residue washed, the filtrate plus washings is diluted to 16 ml and 1 ml of a 0.25 M phosphate solution (containing 0.3 pg iodine as IOj per... 

Most cation exchange occurs in estuaries and the coastal ocean due to the large difference in cation concentrations between river and seawater. As riverborne clay minerals enter seawater, exchangeable potassium and calcium are displaced by sodium and magnesium because the Na /K and Mg /Ca ratios are higher in seawater than in river water. Trace metals are similarly displaced. 

For example, the average atom of potassium spends 10 million years dissolved in the ocean before becoming incorporated into the sediments. (Potassium is in steady state, so its oceanic residence time can be computed by dividing its input rate into the total amount in seawater.) This is plenty of time for ocean mixing, which occius on time scales of a thousand years, to homogenize out any horizontal or vertical concentration gradients. 

The other reason why the average salinity of seawater is 35%o lies in the fundamental chemistry of major ions. For example, the sevenfold increase in the Na /K ratio between river water and seawater (Table 21.8) reflects the lower affinity of marine rocks for sodium as compared to potassium. In other words, the sodium sink is not as effective as the one for potassium. Thus, more sodium remains in seawater, with its upper limit, in theory, being controlled by the solubility of halite. Likewise, the Ca /Mg ° ratio in seawater is 12-fold lower than that of river water due to the highly effective removal of calcium through the formation of biogenic calcite. 

K+ Valinomycin dissolved in diphenyl ether Potassium in feldspar, urine, blood serum, seawater, vegetables 137... 

Potassium is the eighth most abundant element in the Earths crust, which contains about 2.6% potassium, but not in natural elemental form. Potassium is slightly less abundant than sodium. It is found in almost all solids on Earth, in soil, and in seawater, which contains 380 ppm of potassium in solution. Some of the potassium ores are sylvite, carnallite, and polyha-lite. Ore deposits are found in New Mexico, California, Salt Lake in Utah, Germany, Russia, and Israel. Potassium metal is produced commercially by two processes. One is thermochemical distillation, which uses hot vapors of gaseous NaCl (sodium chloride) and KCl (potassium chloride) the potassium is cooled and drained off as molten potassium, and the sodium chloride is discharged as a slag. The other procedure is an electrolytic process similar to that used to produce hthium and sodium, with the exception that molten potassium chloride (which melts at about 770°C) is used to produce potassium metal at the cathode (see figure 4.1). 

Potassium chloride (KCl) is used in drug preparations and as a food additive and chemical reagent. It is possible to reduce the sodium in your diet by substituting potassium chloride for table salt (sodium chloride), which may be healthier. Molten potassium chloride is also used in the electrolytic production of metaUic potassium. KCl is also found in seawater brine and can be extracted from the mineral carnalhte. 

Potassium is found in feldspars and micas, and is the fourth most abundant cation in seawater (390 mg kg-1). Potassium compounds are usually obtained from evaporites (i.e., residues from evaporated water) as KC1 ( potash ) or carnallite, mainly for use in fertilizers. 

Table 5), and several are now being used, or are potentially useful, for measuring key ocean elements. The most common use of direct potentiometry (as compared with potentiometric titrations) is for measurement of pH (Culberson, 1981). Most other cation electrodes are subject to some degree of interference from other major ions. Electrodes for sodium, potassium, calcium, and magnesium have been used successfully. Copper, cadmium, and lead electrodes in seawater have been tested, with variable success. Anion-selective electrodes for chloride, bromide, fluoride, sulfate, sulfide, and silver ions have also been tested but have not yet found wide application. 

Bromine occurs as bromide in seawater (0.188% Br), in the mother liquor from salt wells of Michigan. Ohio. West Virginia. Arkansas, and in the potassium deposits of Germany and France. 

There are three naturally occurring isotopes, 39K through 41K, of which 40K is radioactive with a half-life of 1.3 109 years. Tn ordinary potassium, this isotope represents only 0.0119% of the content. There are four other known isotopes, all radioactive. 33 K and 42K through 44K, all with relatively short half-lives measured in minutes and hours. In terms of abundance, potassium ranks seventh among the elements occurring in the earth s crust. In terms of content in seawater, the element ranks eighth, with an estimated 1,800,000 tons of potassium per cubic mile (388,000 metric tons per cubic kilometer) of seawater, First ionization potential 4,339 eV ... 

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