Colligative Properties Examples

Friedrich Wilhelm Ostwald, a chemist and philosopher, coined the term “colligative properties” in 1891.

We can determine that colligative property is a quality of a substance by the quantity of particles (molecules or atoms) present but not by the nature of the particles. The two examples of colligative properties are the pressure of an ideal gas and the lowering of a solvent’s freezing point due to dissolved particles.

The word “colligative” derives from the Latin word “colligatus,” which means “to be tied together or bound together.” Colligative properties are useful when defining a solution since they show how the properties of the solution are related to the solute concentration in the solution.

Colligative Properties Meaning

Chemical solutions have colligative properties determined by the particles of solute and that of solvent rather than the chemical identity of the solute particles. On the other hand, colligative properties are dependent on the type of solvent. 

The four colligative properties are freezing point depression, boiling point elevation, vapour pressure reduction, and osmotic pressure.

Colligative properties apply to all solutions. However, the equations used to determine them only apply to ideal or weak nonvolatile solute solutions dissolved in a volatile solvent. Calculating colligative characteristics for volatile solutes requires more advanced formulas. A colligative property’s magnitude is inversely related to the solute’s molar mass.

Colligative Properties Examples

When we add a pinch of salt to a cup of water, it freezes at a lower temperature, boils at a higher temperature, has a lower vapour pressure, and changes its osmotic pressure. While colligative properties are usually associated with nonvolatile solutes, we can also observe their effect on volatile solutes.

When we mix alcohol (a volatile liquid) with water, the freezing point drops below the expected value for pure alcohol or pure water. As a result, alcoholic beverages rarely freeze in a household freezer.

Working of Colligative Properties

The dissolved particles displace some of the liquid phase solvent when we introduce a solute to produce a solution. This behaviour lowers the solvent concentration per unit of volume. 

The number of particles rather than the kind matters in a dilute solution. For example, entirely dissolving CaCl2 gives calcium and chloride particles, whereas completely dissolving NaCl yields just two particles (a sodium ion and a chloride ion). 

Table salt would have a stronger effect on colligative characteristics than calcium chloride. Hence, calcium chloride is a more efficient de-icing agent at lower temperatures than common salt.

Colligative Properties

The different types of colligative properties are as follows: 

• Freezing Point Depression

Solution freezing points are lower than the freezing points of pure solvents. The lowering of the freezing point is related to the molality of the solute.

The freezing point of water lowers when we dissolve sugar, salt, alcohol, or any other substance in it. Other than water, the effect operates, although the amount of temperature change varies depending on the solvent.

• Boiling Point Elevation

The boiling factor of a liquid is the temperature at which the vapour strain equals the ambient strain. 

We know that adding a non-volatile liquid to a natural solvent reduces the solution’s vapour strain. We need to raise the temperature of the solution to make the vapour strain equal to the ambient strain. 

The elevation in the boiling factor denotes the difference between the boiling factors of the solution and the natural solvent.

• Vapour Pressure Lowering: 

In a natural solvent, the molecules of the solvent take up the entire floor. When we add a non-volatile solute to a solvent, the floor now contains both the solute and the solvent molecules, reducing the number of solvent molecules blanketing the floor. 

The vapour strain of the solution is smaller than that of the natural solvent at the same temperature since the response’s vapour strain is purely due to the solvent.

• Osmotic Pressure: 

When we place a semi-permeable membrane between a solution and a solvent, solvent molecules pass through the membrane and enter the solution, increasing its volume. The most effective solvent molecules can pass across this semi-permeable barrier, while larger molecules like solute cannot. 

A solution’s osmotic pressure is proportional to the solute’s molar concentration. As a result, the higher the osmotic pressure of the solution, the more solute dissolved in the solvent.

The Van’t Hoff equation describes the relationship between osmotic pressure and solute concentration.

Conclusion

Ostwald hypothesised three different types of solute properties:

• Colligative properties are solely dependent on the concentration and temperature of a solute. They are unaffected by the solute particle’s nature.
• The total qualities of constituent particles determine additive attributes, which are dependent on the chemical makeup of the solute. Mass is an additive property, for example.
• The molecular structure of a solute determines its constitutional qualities.