Why does much of the nation drink fluoridated water? What will be ...

[Marty]

Why does much of the nation drink fluoridated water? What will be an ideal response?

Question 2

What causes overturn in freshwater lakes? What will be an ideal response?

[lolol]

Answer to Question 1

The fluoride ion dissolved in water reduces the incidence of tooth cavities when it is present in
amounts of 1.0 to 1.5 ppm. Tooth enamel and bone are composed of the mineral apatite, whose
structure allows the free substitution of fluoride, chloride, or hydroxyl ions in the mineral structure. In
the presence of fluoride, the crystals of apatite in tooth enamel are larger and more perfect, which
makes them resist decay. Too much fluoride in drinking water, howeverconcentratio ns greater than
4 ppmcan cause childrens teeth to become mottled with dark spots. It took decades and many
studies to prove that fluoride is an effective way to dramatically reduce tooth decay.

Answer to Question 2

Freshwater has a maximum density at 4C. During the summer, surface waters are warmer and less
dense than water at depth. The water of a lake will commonly be layered above and below a boundary
called the thermocline. Cooling of surface water during the winter will cause it to become denser than
underlying water, which weakens the thermocline and causes gravitational instability. The cold surface
water will tend to sink under these conditions, thereby stirring the lake in what is called overturn. This
has the benefit of oxygenating the deep-water layer and preventing it from becoming stagnant.

[Marty]

Excellent

[Joy Chen]

Thanks for the timely response, appreciate it