Search any question & find its solution
Question:
Answered & Verified by Expert
A sample of drinking water was found to be severely contaminated with chloroform ( \(\mathrm{CHCl}_3\) ), supposed to be a carcinogen. The level of contamination was \(15 \mathrm{ppm}\) (by mass).
(i) express this in percent by mass.
(ii) determine the molality of chloroform in the water sample.
(i) express this in percent by mass.
(ii) determine the molality of chloroform in the water sample.
Solution:
1587 Upvotes
Verified Answer
\(15 \mathrm{ppm}\) means 15 parts in million \(\left(10^6\right)\) by mass in the solution.
\(\therefore\) Percentage by mass \(=\frac{15}{10^6} \times 100=15 \times 10^{-4} \%\)
As only \(15 \mathrm{~g}\) of chloroform is present in \(10^6 \mathrm{~g}\) of the solution, mass of the solvent \(=10^6 \mathrm{~g}\)
Molar mass of \(\mathrm{CHCl}_3=12+1+3 \times 35 \cdot 5\)
\(=119 \cdot 5 \mathrm{~g} \mathrm{~mol}^{-1}\)
Moles of \(\mathrm{CHCl}_3=\frac{15}{119 \cdot 5}\)
\(\therefore\) Molality \(=\frac{15 / 119.5 \times 1000}{10^6}=1.25 \times 10^{-4} \mathrm{~m}\)
\(\therefore\) Percentage by mass \(=\frac{15}{10^6} \times 100=15 \times 10^{-4} \%\)
As only \(15 \mathrm{~g}\) of chloroform is present in \(10^6 \mathrm{~g}\) of the solution, mass of the solvent \(=10^6 \mathrm{~g}\)
Molar mass of \(\mathrm{CHCl}_3=12+1+3 \times 35 \cdot 5\)
\(=119 \cdot 5 \mathrm{~g} \mathrm{~mol}^{-1}\)
Moles of \(\mathrm{CHCl}_3=\frac{15}{119 \cdot 5}\)
\(\therefore\) Molality \(=\frac{15 / 119.5 \times 1000}{10^6}=1.25 \times 10^{-4} \mathrm{~m}\)
Looking for more such questions to practice?
Download the MARKS App - The ultimate prep app for IIT JEE & NEET with chapter-wise PYQs, revision notes, formula sheets, custom tests & much more.