A sample of drinking water was found to be severely contaminated with chloroform, `CHCl_(3)`
supposed to be carcinogenic in nature. The level of contamination was 15 ppm ( by mass).
(i) Express this in precent by mass.
(ii) Determine the molality of chloroform in the water sample.

Explanation

(i) 15 ppm means 15 parts of million,
So, Mass percent `= (15xx100)/(10^(6))=1.5xx10^(-3)%`
(ii) Molecular mass of `CHCl_(3)`
`= 12.01+1.0079+(3xx35.45)`
`= 119.367 ~=119` gm/mol
`1.5xx10^(-3)%` means, `1.5xx10^(-3)` gm chloroform in 100 gm
Molality `= ("Weight of solute " xx 1000)/("Molecular mass of solute" xx "Volume of solution (in gm)")`
`=(1.5xx10^(-3) xx 1000)/(119xx100)`
`= 0.000126=1.26xx10^(-4)m`