Parts per billion, and part per million question, plz help???

symptoms of mercury poisoning become apparent after a person has accumulated more than 20 mg of mercury in the body





a) express this amount as parts per million for a 60 kg person.


b) express this amount as parts per billion


c) express this amount as mass/mass percent





what are the units for ppm and ppm anyways? plz explain. thanks!

Parts per billion, and part per million question, plz help???
(a)


20 mg / 60 kg


= 20 * 10^(-3) gm / 60 * 10^3 gm


= 0.333 * 10^(- 6)


= 0.333 ppm.





(b)


If you take billion to mean 10^9, then:


0.333 ppm = 333 parts per billion.





Using 10^12 for billion, the answer is 3.33 * 10^5 parts per billion.





(c)


0.333 * 10^(-6)


= 0.333 * 10^4 %


= 3.33 * 10^3 %.





ppm is a description of what the ratio 0.333 represents. There isn't really any unit, unless you call ppm itself the unit. ppm is dimensionless, as it is just the ratio of two numbers.