Chloroform contamination in drinking water is a serious concern, especially given its potential health risks. Let's break down your question into two parts: converting the concentration from parts per million (ppm) to percent by mass, and then calculating the molality of chloroform in the water sample.
Converting ppm to Percent by Mass
To convert the concentration from ppm to percent by mass, we need to understand what these units mean. Parts per million (ppm) indicates how many parts of a substance are present in one million parts of the solution. In this case, 15 ppm means there are 15 grams of chloroform in one million grams of the water sample.
To convert ppm to percent by mass, we can use the following relationship:
- 1 percent by mass = 10,000 ppm
Using this relationship, we can convert 15 ppm to percent by mass:
Percent by mass = (ppm / 10,000)
Substituting the values:
Percent by mass = (15 ppm / 10,000) = 0.0015
To express this as a percentage, we multiply by 100:
Percent by mass = 0.0015 × 100 = 0.15%
Calculating the Molality of Chloroform
Now, let's determine the molality of chloroform in the water sample. Molality (m) is defined as the number of moles of solute per kilogram of solvent. In this case, chloroform is the solute, and water is the solvent.
First, we need to find the number of moles of chloroform. The molar mass of chloroform (CHCl3) can be calculated as follows:
- Carbon (C): 12.01 g/mol
- Hydrogen (H): 1.01 g/mol
- Chlorine (Cl): 35.45 g/mol × 3 = 106.35 g/mol
Adding these together gives:
Molar mass of CHCl3 = 12.01 + 1.01 + 106.35 = 119.37 g/mol
Next, we calculate the number of moles of chloroform in the sample:
Moles of CHCl3 = mass (g) / molar mass (g/mol)
Given that we have 15 grams of chloroform:
Moles of CHCl3 = 15 g / 119.37 g/mol ≈ 0.125 moles
Now, we need to find the mass of the solvent, which is the water. Since the total mass of the solution is 1,000,000 grams (1 million grams), and we have 15 grams of chloroform, the mass of the water is:
Mass of water = 1,000,000 g - 15 g = 999,985 g
To convert this to kilograms (since molality is expressed in kg), we have:
Mass of water = 999,985 g / 1,000 = 999.985 kg
Now we can calculate the molality:
Molality (m) = moles of solute / kg of solvent
Substituting the values we found:
Molality = 0.125 moles / 999.985 kg ≈ 0.000125 m
Summary of Results
To summarize:
- The concentration of chloroform in the water sample is approximately 0.15% by mass.
- The molality of chloroform in the water sample is approximately 0.000125 m.
This analysis highlights the importance of understanding contamination levels in drinking water and the calculations involved in assessing such risks. If you have any further questions or need clarification on any of these steps, feel free to ask!
