A sample of drinking water was found to be contaminated with chloroform ` (CHCl_3) ` which is considered as cercinogen . The level of contamination was 15 ppm ( by mass)
(i) Express this in percent (by mass)
(ii) Calculate the molarity of chloroform in the water sample.

Explanation

(i) 15ppm = 15 parts in millions `(10 ^(6) ` by mass in solution
` therefore ` Percentage by mass ` = ( 15)/( 119.5)xx 100`
` " " = 15xx 10 ^(-4) %`
(ii) As only 15g of `CHCl_3` is present in 106 g of the solution 1 mass of the solvent =10g
molar mass of `CHCl_3 = 12 xx 1+ xx1 +35-5xx3 = 119.5`
No . of moles of ` CHCl_3 =( 15)/( 119.5) = 0.1255 ` moles
` therefore ` Molarity = `( 0.1255)/( 10^(6)) = 0.1255 xx 10`
` = 1.25 xx 10 ^(-7) m `