Question

A 500 g toothpaste sample has 0.02 g fluoride concentration. What is the concentration of fluorine in terms of ppm levels?
A ) 250
B ) 40
C ) 400
D ) 1000

Answer 1

Hint: PPM represents parts per million. It is the mass of solute (in grams) present in \[{10^6}{\text{g}}\] of solution. Use the following formula for ppm.
\[{\text{ ppm }} = {\text{ }}\dfrac{{{\text{Mass of solute }}}}{{{\text{Mass of solution }}}}{\text{ }} \times {\text{ 1}}{{\text{0}}^6}\]

Complete step by step answer:
The mass of a sample of toothpaste 500 g. The mass of fluoride ions in the sample of toothpaste is 0.02 g. Calculate the concentration of fluorine in terms of ppm levels.
\[{\text{ ppm }} = {\text{ }}\dfrac{{{\text{Mass of solute }}}}{{{\text{Mass of solution }}}}{\text{ }} \times {\text{ 1}}{{\text{0}}^6} \\
{\text{ ppm }} = {\text{ }}\dfrac{{{\text{0}}{\text{.02 }}}}{{{\text{500 }}}}{\text{ }} \times {\text{ 1}}{{\text{0}}^6} \\
{\text{ ppm }} = {\text{ 40 ppm}} \\\]
Hence, the fluoride ion concentration in the toothpaste sample is 40 ppm.
The concentration of 40 ppm for fluoride ions in the toothpaste means that the mass of fluoride ions present in \[{10^6}{\text{g}}\] of toothpaste sample is 40 g.

Hence, the correct option is the option B ).

Additional Information: ppm can also be expressed in the units of mg/kg or µg/kg.
Thus, one ppm represents 1 mg of solute present in 1 kg of solution.

Note: While expressing the concentration in ppm, the amount of solute can be expressed in either grams or millilitre. Similarly the amount of solution can be expressed in either grams or millilitre. Thus ppm is the mass of solute (in grams) present in \[{10^6}{\text{g}}\] of solution. Also, ppm is the volume (in millilitres) of solute present in \[{10^6}{\text{mL}}\] of solution.