Question

If $500g$ pack of colgate toothpaste contains $0.2g$ of fluoride $\left(F^{-}\right)$. Express the concentration of fluoride in terms of $ppm$.

Answer 1

1 ppm can be easily expressed as 1 milligram of substance per kg of parent substance.

In this case $0.2g$ of $F$ in $500g$ toothpaste

$0.4g$ of $F$ in 1kg toothpaste

$400mg$ of $F$ in 1kg toothpaste

so concentration of $F$ is $400ppm$