Question

A sample of drinking water was found to be severely contaminated with chloroform, `CHCl_(3)`, which is supposed to be carcinogenic in nature. The level of contamination was `15 pp m` (by mass).
a. Express this is precent by mass.
b. determine the molarity of chloroform in the water sample.

Answer 1

a. `15 pp m` means `15` parts in million `(10^(6))` parts
`:.` Precent by mass`=15/10^(6)xx100=15xx10^(-4)`
`=1.5xx10^(-3)%`
b. Molar mass of chloroform `(CHCl_(3))=12+1+3xx35.5`
`=118.5 g mol^(-1)`
`100 g` of the sample contains chloroform`=1.5xx10^(-3)g`
`:. 1000 g (1 kg)` of the sample will contain chloroform
`=1.5xx10^(-2) g=(1.5xx10^(-2))/118.5=1.266xx10^(-4) mol`
`:.` Molarity`=1.266xx10^(-4)m`