Which of the following solutions will exhibit highest boiling point? (a) \(0.01 \mathrm{M} \mathrm{Na}_{2} \mathrm{SO}_{4}(\mathrm{aq})\) (b) \(0.01 \mathrm{M} \mathrm{KNO}_{3}\) (aq) (c) \(0.015 \mathrm{M}\) urea (aq) (d) \(0.015 \mathrm{M}\) glucose (aq)

Colligative properties are unique characteristics of solutions that depend solely on the quantity of solute particles, regardless of their identity. These properties include boiling point elevation, freezing point depression, vapor pressure lowering, and osmotic pressure.

Boiling point elevation is a particularly common manifestation of colligative properties and arises because solute particles disrupt the ability of the solvent to evaporate. This disrupts the establishment of equilibrium between the liquid and gas phases at the natural boiling point, thus requiring a higher temperature to achieve boiling.

Real-Life Example of Boiling Point Elevation

For example, when salt is dissolved in water, the boiling point of the resulting solution is higher than that of pure water. This is because the dissolved salt ions interfere with the ability of water molecules to escape into the gas phase. The same principle is applied when salting roads in winter to prevent ice formation – the presence of salt lowers the freezing point of water, preventing it from freezing as easily.

The van't Hoff factor (\( i \)) represents the number of particles a compound breaks down into when it dissolves in a solvent. It's crucial for calculating the magnitude of boiling point elevation and other colligative properties.

For ionic compounds such as NaCl, which dissociates into Na+ and Cl- ions, the van't Hoff factor is 2, indicating it produces two particles per formula unit. Compounds that don't dissociate, like sugar molecules in water, have a van't Hoff factor of 1, as they do not break into smaller particles.

Impact on Boiling Point

In practice, the boiling point elevation of a solution is directly proportional to the van't Hoff factor of the dissolved substance. Using the factor allows us to predict how much the boiling point of a solution will increase compared to the pure solvent. This is why knowing the precise van't Hoff factor is essential for accurately calculating boiling point elevation.

Solute concentration refers to the amount of solute dissolved in a given quantity of solvent, typically measured in molarity (moles per liter). It's another key determinant of colligative properties, including boiling point elevation.

The higher the concentration of a solute in the solvent, the greater the effect on the boiling point. When more particles are present, they further disrupt the ability of the solvent molecules to enter the gas phase, resulting in a higher boiling point elevation.

Comparing Solutions with Different Concentrations

When comparing solutions with different concentrations but the same solute, the solution with the higher solute concentration will have the higher boiling point. This relationship is linear for solutions that follow ideal behavior, meaning that doubling the concentration leads to double the change in boiling point, provided that the van't Hoff factor for the dissolved substance is the same.