The concentration of a solution may be defined as the amount of solute present in the given quantity of the solution.
The concentration of solution may be expressed in several ways as discussed below:
Mass Percentage
The mass percentage of a component in a given solution is the mass of the component per 100 g of the solution.
\[\text{Mass percentage of a component = }\frac{\text{Mass of the component in the solution}}{\text{Total mass of the solution}} × 100\]
Molarity of a solution
The molarity of a solution is defined as the number of moles of the solute dissolved per litre of the solution.It is represented as ′M′. Mathematically,
\[Molarity = \frac{\text{Moles of solute}}{\text{Volume of the solution (in mL)}} × 1000\]
Molality of the solution
The molality of a solution is defined as the number of moles of the solute dissolved per 1000 g (or 1 kg) of the solvent.
Match List-I with List-II.
| List-I (Way of expressing concentration) | List-II (A common use) |
|---|---|
| (A) Mass percentage | (I) Medicine and pharmacy |
| (B) Mass by volume percentage | (II) Commercial bleaching solution of sodium hypochlorite |
| (C) Mole fraction | (III) Concentration of pollutants in water or atmosphere |
| (D) Parts per million | (IV) Relating the vapour pressure of a solution with its concentration |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → A-II, B-I, C-IV, D-III
Each way of expressing concentration has its own merits, so each is preferred in a particular field.
(A) Mass percentage — This matches (II) Commercial bleaching solution of sodium hypochlorite. Mass percentage is common in industrial chemical applications; commercial bleaching solution contains 3.62 mass percentage of sodium hypochlorite.
(B) Mass by volume percentage — This matches (I) Medicine and pharmacy. It gives the mass of solute in 100 mL of solution and is commonly used in medicine and pharmacy.
(C) Mole fraction — This matches (IV) Relating the vapour pressure of a solution with its concentration. It is also useful in calculations on gas mixtures.
(D) Parts per million — This matches (III) Concentration of pollutants in water or atmosphere. Pollutants are present in trace quantities, for which ppm is convenient.
NCERT (2026-27 edition):
1.2 Expressing Concentration of Solutions – “Concentration described by mass percentage is commonly used in industrial chemical applications. For example, commercial bleaching solution contains 3.62 mass percentage of sodium hypochlorite in water.”
“(iii) Mass by volume percentage (w/V): Another unit which is commonly used in medicine and pharmacy is mass by volume percentage.”
“…The concentration of pollutants in water or atmosphere is often expressed in terms of μg mL–1 or ppm.”
“Mole fraction unit is very useful in relating some physical properties of solutions, say vapour pressure with the concentration of the solution and quite useful in describing the calculations involving gas mixtures.”