Colligative and Propeties of Solution

Colligative and Propeties of Solution

What Are Colligative Properties ?

The term of  “colligative” comes from Latin word “colligare” which means “to gather”. Colligative properties are properties of solution that do not depend on the identity of the solutes, but on the number of dissolved particles in the solution. There are two kinds of colligative properties,namely :

-          Colligatigative properties of nonelectrolyte solutions

-          Colligative properties of electrolyte solutions

What Properties belong to Colligative Properties of Solution ?

The formation of solution, from solute and solvent, only gives a small effect to the chemical properties of solute. Its physical property, however, will drastically change. Colligative properties of solution is The vapor pressure of the pure solvent is higer then that of solution, The boiling point of the pure solvent is lower thanthat of the solution, The freezing point of the pure solvent is higer than that of the solution. It means that the presence of a solute can cause : the pavor pressure lowering, the boiling point evaluation, and the freezing point depression. The properties are know as colligative properties of solution. The osmotic pressure, which arises from osmosis between two solutions with different concentrations, is also know as colligative properties of solution.

 The Vapor Pressure Lowering

Vapor pressure : If a liquid is placed in a closed container, it will evaporate. The liquid particles will decrease while the gaseous particles will increase. As the gaseous particles increase, they will bounce around and turn back into liquids or undergo condensation. The evaporation and the condensation rates equilibirium is reached. At equilibrium, the evaporation and the condensation rates will be the same. When these particles hit the wall of the container, they exert a pressure. This pressure in this equilibrium  is called the saturated vapor pressure of the liquid or vapor pressure of the liquid.

The value of vapor pressure depends on the identities of substance and temperature. Subtances with high vapor pressure are easily evaporated, and they are called volatile substances, such as ethanol and ether. While substances with low vapor pressure are hardly evaporated (nonvolatile), for examples water,glycol, and glycerol.

The solute molecules and the solvent molecules attract each other. It eans that the solute molecules it causes the vapor pressure of solution is than that of the pure solvent. The difference between the vapor pressure of the pure solvent and that of a solution is called the vapor pressure lowering. This phenomenon was discovered for the first time by a French chemist, Francois-Marie Raoult. Raoult stated that the addition of a nonvolatile solute to a solvent led the lowering of vapor pressure.

The Boiling Point Elevation

Have you ever seen boiling water ? A liquid boils when its saturated vapor pressure becomes equal to the external pressure. The normal boiling point of a liquid is a temperature at which the vapor pressure equals to 1 atmosphere. For example, the normal boiling point of water is 100C. But at a different pressure, water will boil at different temperature. For example, at the top mountain the pressure is lower, so the noiling point of water will also be lower than 100 C. You have learned that a nonvolatile solute in solution causes the lowering of vapor pressure.

The Freezing Point Depression

The freezing point or melting point of a solution is the temperature at which solid and liquid are in equlibirium. The most generic solid-liquid equilibrium is water and ice at 0C and 1 atmosphere . This dynamic equilibrium can be illustrated by a glass of ice that is set in 0C. At this temperature, Ice starts melting. At the same time, water also freezes and merges with the ice block. This equilibrium will change if tempratute raises or drop.

The Osmotic Pressure

The process where a solvent passes throught a asemipermeable membrance from one solution to another (or from a pure solvent into a solution) is called osmosis. Osmosis process will last until equilibrium is reached. It can be seen when the volume of a solution stop changing. The volume difference between the two solutions at the equilibrium generates a pressure called the osmotic pressure. The osmotic pressure is defined as a pressure given to prevent osmosis process, which is to prevent the flow of solvent molecules.

Colligatives Properties in Daily Life

Colligatives properties, especially the freezing point depression, have so many uses in daily life. The applications of freezing point depression can survive many lives during cold season. The application of freezing point depression :

1  .       Ice Cream Making .

     What is he difference between ice block and ice cream ? ice block is so hard and has no taste because ice block is only water that freezes. Wheares, ice cream is soft and delicious. The ingredients of ice cream, such as sugar, milk, chocolate, butter, and salt lower freesing point of water and make ice cream cold and soft but no frozen.

      2  .       Antifreeze in Car Radiator. In a cold region, people often apply an antifreeze agent such as ethylene glycol to their car radiator. Do you know why ? In cold region, water in radiator easily freezes. If it happens continuously, the car engine will damage. A solution of ethylene glycol in the radiator water can lower the freezing point, so the water will not freezing easly.

3   .       Antifreeze to melt snow. In certain regions, every winter, snow drops over the streets, of course, it makes vehicles difficult to move. People often put salt, such as Nacl and Cacl_2,on the roads after a snowfall to melt the snow. The more salt are spread, the more snow will melt (the less snow will freeze).

References (Yudistira,kimia for senior high school jilid xii)