# Answer to Question #4329 in Other Chemistry for sarah

Question #4329
You are the public health officer in the water treatment facility for a city of 50,000 people. A concentration of 1.0 ppm of flourine in the drinking water is sufficient for the purpose of helping to prevent tooth decay. (1 ppm means &quot;one part per million,&quot; or 1 g of flourine per one million grams of water). The compound normally chosen for flouridation is the same as is found in some toohtpaste&#039;s sodium flouride. You know that sodium flouride is 45% flourine by mass. Calculate how many kilograms of sodium flouride you will need to have in order to flouridate the city&#039;s water supply for one year, based upon your estimate that the average daily consumption of water is 150 gallons per person. (1 gallon = 3.79 L; 1 year = 365 days; 1 ton = 2000 lb; 1 lb = 456.3 g; density of water = 1.0 g/mL )
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2015-10-02T03:48:17-0400
Vgeneral(H2O) = 50 000*150*3.79*365 = 1.4*1010 L
m general(H2O) = 1.4*1010*1 = 1.4*1010 kg
m(F)H2O = m(F)/(m(F) + m(H2O))(10^-6) = m(F)/(m(F) + 1.4*10^10)*(10^-6)
m(F) = 1.4*10^4 kg
(NaF) = 1.4*10^4/0.45 = 2.3*10^4 kg

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Assignment Expert
05.10.15, 13:37

Dear Kira,
1) mass = volume × density. Density of water equals 1 kg/L. That's why m = 1.4×1010 L × 1 kg/L = 1.4×1010 kg;
2) mass of F can be 1 kg per 1000000 kg of water, or 1 g per 1000000 g of water (thanks, there was a mistake in the previous comment);
3) to find the mass of F we need to find million part of water mass (million part of 1.4×1010). That's why we divide 1.4×1010 by 106 (1000000).

Kira
03.10.15, 07:45

Thank you for your quick reply! I still have few questions. How did you get the mass of water is 1.4x10^10 kg? And why the mass of F is 1g per 1000000 kg of water? Isn't "1g of flourine per million GRAMS of water"?And why do you have to divided 100000 by 1.4x10^10?

Thanks!!!

Assignment Expert
02.10.15, 11:59

Dear Kira,
1.Calculate the volume and mass of water needed to supply a city: 1.4×1010
kg.
2.Calculate the mass of fluorine (F) needed for preventing tooth decay: 1 kg per
1000000 kg of water, mass (F) = 1.4×1010/106 = 1.4×10kg.
3. Calculatethe amount of NaF needed (NaF consists of 45% of F): 1.4×104/0.45 = 2.3×104
kg.

Kira
02.10.15, 09:45

Still comfused!! would you mind explain?