The concentration of chloride ions in a water sample is 250 ppm. Calculate this concentration in mol dm⁻³.

Question

Quizplus · Accepted Answer

To convert from ppm (parts per million) to mol dm^-3:

1. Calculate the mass of the solute in the sample:
250 ppm = 250 mg/L (since 1 ppm = 1 mg/L in water)
If we assume that the sample has a volume of 1 L, then the mass of chloride ions in the sample is 250 mg.

2. Calculate the number of moles of the solute:
The molar mass of chloride ions (Cl-) is 35.5 g/mol.
So, the number of moles of chloride ions in the sample is:
250 mg / 35.5 g/mol = 0.00704 mol

3. Calculate the concentration in mol dm^-3:
If we assume that the sample has a volume of 1 L, then the concentration of chloride ions is:
0.00704 mol / 1 L = 7.04 mM

Therefore, the answer is B) 7.1 mM (rounded to one decimal place).

The Concentration of Chloride Ions in a Water Sample Is