Question

A sample of drinking water severely contaminated with chloroform, $CHCl _{3}$, is supposed to be carcinogenic in nature. The level of contamination was $15 \,ppm$ (by mass) What is the molality of chloroform in the water sample?

• A. $2.25 \times 10^{-5} m$
• B. $1.25 \times 10^{-4} m$
• C. $1.85 \times 10^{-6} m$
• D. $1.72 \times 10^{-5} m$

Answer 1

Answer: (B)

$15 \,ppm$ means $15\, g$ of $CHCl _{3}$ are dissolved in $10^{6} g$ of solvent. Molality $=\frac{w_{B} / m_{B}}{\text { Mass of solvent }} \times 1000$

$w_{B}=15 \,g , m_{B}=119.5, M_{B}=10^{6} g$

Molality $=\frac{15 / 119.5}{10^{6}} \times 1000$

$=1.25 \times 10^{-4} m$