Question

It is recommended the drinking water contain 1.6 ppm fluoride (F-) to prevent tooth decay. Consider a cylindrical reservoir with a diameter of 5.00 x 102 m and a depth of 20.0 m (the volume of a cylinder = r2h). How many grams of fluoride should be added to give 1.6 ppm? Fluoride is provided by dissolving H2SiF6. How many grams of H2SiF6 contain this amount of fluoride?

Answer #1

**radius = d/2 = ( 500 /2) = 250 m , h = 20m**

**volume of cylinder = p x r^2 x h = ( 3.14 x 250^2 x 20)
= 3925000 m^3 = 3925000 x 1000 L**

**we need 1.6 ppm F- for 3925000 x 1000
L**

**1.6 ppm means 1.6 mg of F- per
1Liter ( 1ppm = 1mg/L)**

**hence for 3925000 x 1000 Liters F-mass = ( 1.6 x 3925000
x 1000)mg = 628 x 10^7 mg = 628 x 10^4 g**

**Hence we need 6.28 x 10^ 6 grams**

**Moles of F- = mass of F- / atomic mass of F- = 6.28x10^6
/ 19 = 3.305 x 10^5**

**each H2SiF6 gives 6 F-**

**henceH2SiF6 moles = ( 3.305x10^ 5) / 6 = 5.5088 x
10^4**

**Mass of H2SiF6 = moles of it x molar mass of H2SiF6 =
5.5088 x 10^4 x 144.09 = 7.937 x 10^ g**

It is recommended that drinking water contain 1.6 ppm fluoride
(F−) for prevention of tooth decay. Consider a reservoir
with a diameter of 4.70 ✕ 102 m and a depth of 14.2 m.
(The volume is πr2h, where
r is the radius and h is the height.) How many
grams of F− should be added to give 1.6 ppm? &
Fluoride is provided by hydrogen hexafluorosilicate,
H2SiF6. How many grams of
H2SiF6 contain this much F−?

To aid in the prevention of tooth decay, it is recommended that
drinking water contain 0.700 ppm fluoride (F–).
a) How many grams of F– must be added to a cylindrical water
reservoir having a diameter of 3.01 × 102 m and a depth of 75.43 m?
(b) How many grams of sodium fluoride, NaF, contain this much
fluoride?

To aid in the prevention of tooth
decay, it is recommended that drinking water contain 0.800 ppm
fluoride (F–).
(a) How many grams of F– must be added to a cylindrical water
reservoir having a diameter of 8.96 × 102 m and a depth of 23.16
m?
(b) How many grams of sodium fluoride, NaF, contain this much
fluoride?

To aid in the prevention of tooth decay, it is recommended that
drinking water contain 0.800 ppm fluoride (F–). (a) How many grams
of F– must be added to a cylindrical water reservoir having a
diameter of 2.44 × 10^2 m and a depth of 17.27 m? (b) How many
grams of sodium fluoride, NaF, contain this much fluoride?

Water is fluoridated to prevent tooth decay. (a) How many liters
of 1.0 M H2SiF6 should be added to a reservoir with a diameter of
100 m and a depth of 20 m to give 1.2 ppm F2? (1 mol H2SiF6
provides 6 mol F.) (b) How many grams of solid H2SiF6 should be
added to the same reservoir to give 1.2 ppm F2?
The answers are A: 1.7 x 10^3 L and B: 2.4 x 10^5 g
I just...

Fluoride ion is poisonous in relatively low amounts: 0.2 g of F
- per 70 kg body weight can cause death. Nevertheless, in order to
prevent tooth decay, F - ions are added to drinking water at a
concentration of 1 mg of F - ion per L of water.
How many liters of fluoridated drinking water would a 70 kg person
have to consume in one day to reach this toxic level?
How many kilograms of sodium fluoride would...

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