Fluoride ions drinking water

As far as the addition of fluoride to drinking water is concerned, the key requirement is that the compound chosen should yield free fluoride ions readily on dissolution in water [123]. Sodium fluoride can be used as it is reasonably soluble and dissolves readily [124]. However, even by the 1950s it was proving relatively expensive, and so the use of alternative compounds was investigated [125]. This identified fluorosilicic acid and its disodium salt as possible alternatives (Table 4), and their use as the source of fluoride in drinking waters continues to this day. 

Fluorine is widely distributed in Nature, representing about 0.065% of the earth s crust, making it the 13th most abundant element. It is more abundant than chlorine and much more abundant than common metals such as zinc and copper. Fluorine occurs in many minerals in which fluoride ion replaces hydroxide. The conversion of hydroxyapatite to flu-oroapatite strengthens tooth enamel. However, this would result in an increased brittleness in bones. An untested theory is that the widespread use of fluoride in drinking water, which had remarkable benefits in preventing dental caries in the 1960s, may be the cause of the rise in osteoporosis in the elderly population. 

Tooth enamel is composed of the mineral hydroxyapatite, Ca5(P04)s0H, which has a Ksp of 6.8 X 10 . The molar solubility of hydroxyapatite is 2.7 x 10 mol/L. When hydroxyapatite is reacted with fluoride, the OH is replaced with the F ion on the mineral, forming fluorapatite, Ca5(P04)3F. (The latter is harder and less susceptible to caries.) The Ksp of fluorapatite is 1 x 10 °. Calculate the solubility of fluorapatite in water. Given your calculations, can you support the fluoridation of drinking water Your answer must be within 0.5%. 

EXPERIMENT 13 POTENTIOMETRIC DETERMINATION OF FLUORIDE IN DRINKING WATER USING A FLUORIDE ION-SELECTIVE ELECTRODE ... 

Fluoridation of drinking water is employed in many places to aid in the prevention of tooth decay. Typically the F ion concentration is adjusted to about 1 ppb. Some water supplies are also hard that is, they contain certain cations such as Ca that interfere with the action of soap. Consider a case where the concentration of Ca is 8 ppb. Could a precipitate of Cap2 form under these conditions (Make any necessary approximations.)... 

Most t5q3es of water contain fluoride ions. The fluoride concentration of the different water samples ranges from traces to 10 mg/dm . From the 1930s, it has been known that low concentration (0.5-1.5 mg/dm ) of fluoride in drinking water is beneficial in... 

Overly high conventrations of nitrate (limiting value in Table 23.1) can be reduced by bacterial denitrification, ion exchange, or reverse osmosis. The fluoridation of drinking water is discussed in 7.3.2.10. 

F H. T. Dean et al. put the correlation between decreased incidence of dental caries and the presence of fluoride ions in drinking water on a quantitative basis... 

Table 4. Sources of fluoride ion and their use in drinking water in the United States [125]...

Second, these materials are unable to undergo fluoride recharge [283], Their predominantly hydrophobic composition means that there is no basis for interaction with, or uptake of, the strongly hydrophilic F ion in situ. Hence, exposure to fluoridated drinking water or fluoridated toothpastes has no effect, and these materials are unable to function as fluoride reservoirs [284],... 

FICs are useful as electrochemical sensors, electrolytes and electrodes in batteries and in solid state displays (Farrington Briant, 1979 Ingram Vincent, 1984). If a FIC material containing mobile M ions separates two compositions with different activities of M, a potential is set up across the FIC that can be related to the difference in the chemical activities of M. By fixing the activity on one side, the unknown activity on the other can be determined. This principle forms the basis of a number of ion-selective electrodes LaFj doped with 5% SrF2 is used for monitoring fluoride ion concentration in drinking water. Similarly, calcia-stabilized-zirconia is used in cells of the type... 

Fluoride ion tends to replace the isoelectronic ion OH- in solids. In particular, hydroxyapatite, Cas O OH, the chief constituent of tooth enamel, reacts slowly with aqueous fluoride to form fluoroapatite, which is harder and more resistant to tooth decay. The dental profession therefore advocates fluoride treatments at the time of regular dental checkups, and also (primarily to provide for the dental health of children) the presence of 0.7-1.0 ppm natural or added F in drinking water. Too much (>4 ppm) F in water, however, is acknowledged to cause mottling of teeth and bone sclerosis. Thus, the range of concentrations over which fluoride in public drinking water is considered to be beneficial is rather narrow. 

The effect of pH on solubility is also important in understanding how fluoride ion reduces tooth decay. When tooth enamel comes in contact with F ions in drinking water or fluoride-containing toothpaste, OH- ions in hydroxyapatite, Ca5(PC>4)30H, are replaced by F- ions, giving the mineral fluorapatite, Ca5(PC>4)3F. Because F- is a much weaker base than OH-, Ca5(P04)3F is much more resistant than Cas(P04)30H to dissolving in acids. 

Fluoride (F ) is a halogen ion that occurs in many potable and wastewaters. It may also occur in soils, sediments, hazardous waste, aerosol, and gas. While a low concentration of fluoride (below 1 ppm at controlled level in drinking water) is beneficial for reducing dental caries, a higher content is harmful. Fluoride in water may be determined by one of the following methods ... 

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