Solutions are homogeneous systems that contain two or more components, as well as products that are the result of the interaction of these components. They can be in solid, liquid or gaseous state. Consider the liquid state of aggregation of solutions. Their composition includes a solvent and a substance dissolved in it (the latter is less).
The colligative properties of solutions are their characteristics that are directly dependent only on the solvent and concentration of the solution. They are also called collective or common. The colligative properties of solutions are manifested in mixtures in which there is no interaction of a chemical nature between their constituent components. In addition, the forces of mutual action between the particles of the solvent and the particles of the solvent and the substance dissolved in it are equal in ideal solutions.
Colligative properties of solutions:
1) The vapor pressure is lower over the solution than over the solvent.
2) The crystallization of the solution occurs at a temperature below the crystallization temperature of the solvent in its pure form.
3) The solution boils at a higher temperature than the solvent itself.
4) The phenomenon of osmosis.
Let us consider colligative properties separately.
The equilibrium at the phase boundary in a closed system: liquid - vapor is characterized by saturated vapor pressure. Since part of the surface layer in the solution is filled with solute molecules, equilibrium will be achieved with a lower vapor pressure.
The second collegial property — the decrease in the crystallization temperature of the solution as compared to the solvent — is due to the fact that the particles of the solute interfere with the construction of crystals and thereby prevent crystallization at lower temperatures.
The boiling point of the mixture is higher than the solvent in its pure form, due to the fact that the equality of atmospheric pressure and saturated vapor pressure is achieved with greater heating, since some of the solvent molecules are associated with particles of the dissolved substance.
The fourth collegiate property of solutions is the phenomenon of osmosis.
The phenomenon of osmosis is the ability of a solvent to migrate through a septum, which is permeable to some particles (solvent molecules) and impermeable to others (dissolved substance molecules). This septum separates a solution with a high solute content from a less concentrated solution. An example of such a semi-permeable septum is the membrane of a living cell, a bull’s bubble , etc. The phenomenon of osmosis is due to equalization of concentrations on both sides, separated by a membrane, which is thermodynamically more beneficial for the system. Due to the movement of the solvent into a more concentrated solution, an increase in pressure is observed in this part of the vessel. This excess pressure is called osmotic.
The colligative properties of solutions of non-electrolytes can be mathematically represented by the equations:
∆ bp = bk ∙ cm;
∆ Tcr. = Kzam ∙ cm;
π = CRT.
Colligative properties in numerical terms differ for electrolyte solutions and non-electrolyte solutions. For the first they are somewhat larger. This is due to the fact that electrolytic dissociation occurs in them , and the number of particles increases significantly.
The colligative properties of solutions are widely used in everyday life and in production, for example, the phenomenon of osmosis is used to produce pure water. In living organisms, many systems are also built on the colligative properties of solutions (for example, plant cell growth).