Calculation of Molality of Chloroform in Water Sample
To determine the molality of chloroform in the water sample containing 15 ppm chloroform by mass, we will first need to convert the given concentration from parts per million (ppm) to molality.

Step 1: Convert ppm to mass fraction
In order to convert ppm to mass fraction, we need to use the formula:
\[ \text{Mass Fraction (w)} = \frac{\text{ppm} \times 10^{-6}}{1} \]
Given that the water sample contains 15 ppm of chloroform, we can calculate the mass fraction of chloroform in the sample:
\[ w = 15 \times 10^{-6} = 0.000015 \]

Step 2: Calculate molality
Now that we have the mass fraction of chloroform in the water sample, we can proceed to calculate the molality using the formula:
\[ \text{Molality (m)} = \frac{\text{Mass Fraction (w)}}{\text{Molar Mass of Chloroform} \times \text{Density of Water}} \]
The molar mass of chloroform (CHCl3) is approximately 119.38 g/mol, and the density of water is 1 g/mL. Plugging in these values:
\[ m = \frac{0.000015}{119.38 \times 1} = 1.26 \times 10^{-7} \text{mol/kg} \]
Therefore, the molality of chloroform in the water sample is approximately 1.26 x 10^-7 mol/kg. This represents the concentration of chloroform in the water sample in terms of the number of moles of chloroform per kilogram of water.

0.000125