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        a sample of drinking water was found to be severely contaminated with chloroform CHCl 3 supposed to be a carcinogen the level of contamination was 15ppm by mass 	express this in % mass 	determine the molality of chloroform in the water sample
7 months ago

## Answers : (2)

Arun
22557 Points
							Dear student

1) 15 ppm means 15 parts in 1 millions (10^6)
and percentage always for 100

hence 15 ppm = (15/10^6 )*100
= 15*10^-4
= 1.5*10^-3
2) molar mass of chloroform = 118.5g/ mol

from percentage by mass 100 gram of sample has 1.5*10^-3 g of chloroform
then 1000 gram of sample has = 1.5*10^-3 g * 1000 gram/ 100 gram
= 1.5*10^-2 g

molality = moles of solute / mass of solvent in Kg

moles of solute = mass of solute / molar mass
= 1.5*10^-2/ 118.5
=1.266*10^-4 moles

molality =  1.266*10^-4 moles/ 1 Kg =1.266*10^-4 m

Regards
Arun


7 months ago
Soumendu Majumdar
159 Points
							Dear Aiden,PPM refers to parts per million or (mass of chloroform) x $10^{6}$ divided by the total mass--Equation 1Mass percentage refers to the mass of chloroform x $10^{2}$ divided by the total mass--Equation 2So dividing Equation 2 by Equation 1 we getMass percentage =  $15\times 10^{2}/ 10^6$ = $15\times 10^{-4$Now molality is defined as the ratio of the number of moles of solute divided by the mass of solvent in kgThe molecular mass of chloroform or mass of 1 mole of chloroform is 119.38 g/mol (you may round it off as 119.5 or 120 g/mol as required)Now out of 100g of the solution, the mass of chloroform is $15\times 10^{-4$ gSo the mass of solvent = $100-15\times 10^{-4$ g = 99.9985 g (You may round it off as 100 g)= 0.0999985 kg (can be rounded off to 0.1 kg)Now the number of moles of chloroform = $15\times 10^{-4}/119.38$So molality = $15\times 10^{-4}/119.38 \times 0.0999985$ mol/kg= $1.2565\times 10^{-4}$ mol/kgHope this helps!regards,Soumendu

7 months ago
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