Question

How many gram of sodium fluoride should be added to 100000 liter of drinking water containing 0.6 ppm of sodium fluoride to provide a recommended concentration of 1.75 ppm?

Answer is 115 grams. I keep getting .115 g What am I doing wrong? Please help.

Answer 1

Nevermind. I figured it out.

Key was 1 ppm is 1mg/L.

1.15 mg/L * 100,000 L = 115,000 mg (115g)

Answer 2

If a topical cream contains 1.8% (w/w) of hydrocortisone, which of the following strengths is equivalent?

Answer 3

1.75 ppm-0.6 ppm= 1.15 ppm

Since 1 ppm is equivalent to 1 mg/L, 1.15 ppm is equal to 1.15 mg/L.

Therefore,

1.15 mg/L x 100,000L = 115, 000 mg

Since grams are needed, 115, 000 mg x 1g/ 1000 mg = 115 g.

Hope this helps.