A sample of drinking water was found to be severely contaminated with chloroform \((CHCl_3)\) supposed to be a carcinogen. The level of contamination was 15ppm (by mass): (i) express this in percent by mass (ii) determine the molality of chloroform in the water sample.
(i) 15 ppm (by mass) means 15 parts per million \((10 ^6 )\) of the solution. Therefore, percent by mass \(=(\frac{15}{10^6})\times100\% \) \(= 1.5 \times 10^{ - 3} \%\) (ii) Molar mass of chloroform \((CHCl_3) = 1\times12 + 1\times1 + 3\times35.5\) \(= 119.5 \,g mol^{ - 1}\) Now, according to the question, 15 g of chloroform is present in \(10^6 g\) of the solution. i.e., 15 g of chloroform is present in \((10^6 - 15) ≈ 10^6 g\) of water. Molality of the solution \(=\frac{(\frac{15}{119.6} mol) }{(10^6\times10^{-3})}\) \(=1.26 × 10^ {- 4} m\)
It is the amount of solute present in one liter of solution.
Concentration in Parts Per Million - The parts of a component per million parts (106) of the solution.
Mass Percentage - When the concentration is expressed as the percent of one component in the solution by mass it is called mass percentage (w/w).
Volume Percentage - Sometimes we express the concentration as a percent of one component in the solution by volume, it is then called as volume percentage
Mass by Volume Percentage - It is defined as the mass of a solute dissolved per 100mL of the solution.
Molarity - One of the most commonly used methods for expressing the concentrations is molarity. It is the number of moles of solute dissolved in one litre of a solution.
Molality - Molality represents the concentration regarding moles of solute and the mass of solvent.
Normality - It is the number of gram equivalents of solute present in one liter of the solution and it is denoted by N.
Formality - It is the number of gram formula present in one litre of solution.
