Colligative properties are properties of solvents which are affected by the number of particles into which a solute separates when mixed with a solvent.
The four Colligative Properties are:
- Lowering of Vapour Pressure: When you add a solute (substance to be dissolved) to a solvent (substance that will dissovle solute) you will have some solute molecules that linger at the surface of the liquid. Once the solute is dissolved into the solvent, the amount of solvent molecules hovering over the surface (vapor) will decrease and so the vapor pressure of the solvent has decreased.
- Depression of Freezing Point: The presence of a solute lowers the freezing point in a solution. It is lower than the freezing point of the pure solvent alone. The exact change (?T) can be calculated as van't Hoff Factor (i) of the solute multiplied by its molality (m) multiplied by the freezing point depression constant of the solvent (Kf): ?T = i(?Kf)m. Alternatively, it can be calculated as the total molality of all solutes in solution times the depression constant: ?T = Kf ? m.
- Elevation of boiling point: Because of the lowered vapor pressure, the boiling point of a solution is higher than the pure solvent would have by itself. The change in boiling point (?T) can be calculated in the same way as the change in freezing point, except a different constant is used: the van 't Hoff factor (i) of the solute multiplied by its molality multiplied by the boiling point elevation constant of the solvent (Kb): ?T = iKbm. ?T can also be calculated using the sum of all molalities: ?T = Kb ? m.
- Osmotic Pressure: The presence of solute can cause pressure to be exerted across a semipermeable membrane according to an equation quite similar to the ideal gas law: ? is the osmotic pressure, n is the number of moles of solute, R is the ideal gas constant, T is the absolute temperature in Kelvin, and V is the volume: ? = (nRTi)/V.
I hope this will be helpful for those who are new to this concept..........
Don't forget to Rate me./...........
Back to Community Shelf
4 Nickels awarded!![[Post New]](/templates/default/images/icon_minipost_new.gif){kind=icon}
414
