Toothpastes containing fluoride ions help protect against tooth decay - Leaving Cert Chemistry - Question 1 - 2021

To find the mass of fluoride in 1.0 cm³ of toothpaste with a concentration of 1,360 p.p.m., we first interpret the concentration:

1,360 p.p.m. means 1,360 mg of fluoride per liter of toothpaste.

Next, we convert 1.0 cm³ to liters:

$$1.0 ext{ cm}^3 = 0.001 ext{ L}$$

Now, we can find the mass of fluoride in 1.0 cm³ by using the concentration:

$$ext{Mass} = ext{Concentration} imes ext{Volume}$$

Substituting the known values:

$$ext{Mass} = 1,360 ext{ mg L}^{-1} imes 0.001 ext{ L} = 1.36 ext{ mg}$$

Thus, the mass of fluoride in 1.0 cm³ of the toothpaste is 1.36 mg.