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.(ii) determine the molality of chloroform in the water sample.

(i) To convert parts per million (ppm) to percent by mass, you simply divide by 10,000 because 1% = 10,000 ppm. So, 15 ppm = 15/10,000 = 0.0015% by mass.

(ii) To determine the molality of chloroform in the water sample, we first need to know the molar mass of chloroform (CHCl3). The molar mass of CHCl3 is approximately 119.38 g/mol.

Molality (m) is defined as the number of moles of solute per kilogram of solvent. In this case, the solute is chloroform and the solvent is water.

First, we need to convert ppm to grams. Since ppm is parts per million, 15 ppm of chloroform is equivalent to 15 g of chloroform in 1,000,000 g of water.

Next, we convert the mass of chloroform to moles.

Number of moles = mass/molar mass = 15 g / 119.38 g/mol = 0.1257 moles

Then, we convert the mass of water to kilograms.

1,000,000 g = 1000 kg

Finally, we can calculate the molality.

Molality (m) = moles of solute / kg of solvent = 0.1257 moles / 1000 kg = 0.0001257 mol/kg or 0.1257 mmol/kg.

(i) To convert parts per million (ppm) to percent by mass, you need to understand that 1% is equivalent to 10,000 ppm. Therefore, to convert 15 ppm to percent, you divide 15 by 10,000.

15 ppm / 10,000 = 0.0015%

(ii) To determine the molality of chloroform in the water sample, you need to know the definition of molality. Molality (m) is defined as the number of moles of solute per kilogram of solvent.

First, let's convert 15 ppm to grams. Since ppm stands for parts per million, 15 ppm means there are 15 grams of chloroform in 1 million grams of water.

Next, convert the mass of water to kilograms (since molality is in terms of kilograms of solvent). 1 million grams is equal to 1,000 kilograms.

Now, we need to find the number of moles of chloroform. The molar mass of chloroform (CHCl3) is about 119.38 g/mol.

So, the number of moles of chloroform = mass/molar mass = 15 g / 119.38 g/mol = 0.1257 mol

Finally, we can find the molality by dividing the number of moles of chloroform by the mass of the water in kilograms.

So, molality (m) = number of moles of solute / mass of solvent in kg = 0.1257 mol / 1000 kg = 0.0001257 mol/kg or 0.0001257 m.