Question

A 500 g toothpaste sample has 0.2 g of fluoride. The concentration of fluoride ions in terms of ppm level is ___.

• A. 250 ppm
• B. 200 ppm
• C. 400 ppm
• D. 1000 ppm

Answer 1

The correct option is C 400 ppm

Mass of solute (i.e. concentration of $F^{-}$ ion) = 0.2 g in 500 g
Concentration in ppm $=\frac{\text{weight of fluoride ion}\left(g\right)}{\text{total weight of toothpaste (g)}}\times {10}^6$
Concentration of fluoride ion in ppm $=\frac{0.2}{500}\times {10}^6=400$ ppm