Question 20 of 50intermediate🔧 ApplyNumerical2 marks
A sample of drinking water was found to be severely contaminated with chloroform (CHCl3) supposed to be a carcinogen. The level of contamination was 15 ppm (by mass):
(i)
express this in percent by mass
Answer
15 ppm = ⁻⁴ % = 0.0015% by mass
(ii)
determine the molality of chloroform in the water sample.
Answer
Molality of chloroform = ⁻⁴ mol/kg (or ⁻⁴ m)
Explanation
This question tests the conversion between different concentration units. For ppm to percent by mass, we use the relationship that 1 ppm = 10⁻⁴ %. For molality calculation, we need to find moles of solute and mass of solvent in kg. Since the solution is very dilute (15 ppm), the mass of solvent is approximately equal to the mass of solution.