Colligative Properties of Solutions Boiling Point and Freezing Point

Freezing Point Depression Refers to the decrease in the freezing point of a pure liquid when another substance is dissolved in the liquid Freezing point of a solution is lower than that of a solvent Freezing point is the temperature when the liquid and solid phases are in equilibrium.

Why do we have to add salt on icy roads during winter? Addition of salt on icy roads will make some of the salt particles dissolve in a thin layer of water on the icy surface. As a result, the equilibrium between the ice and the aqueous layer is disturbed because the vapor pressure of the solution in contact with the ice is lower than the vapor pressure of water. This result to melting of ice and lowering the freezing point of a solution.

Describe the heat transfer that occurred to make the ice cream? What absorbed heat and what lost heat? The ice mixture loses heat. The ice absorbs the heat from the ice cream mixture. The ice melts as it absorbs the heat. The ice cream mixture freezes as it loses heat

Boiling Point Elevation Boiling point is the temperature at which liquid’s vapor pressure reaches atmospheric pressure Boiling point of a solution is higher than that of a pure solvent Vapor pressure of an aqueous solution is less than that of pure water at the same temperature Why? Because the presence of solute particles lowers the concentration of solvent molecules at the liquids surface

Vapor pressure vapor pressure pure liquid > solution solute solvent  The molecules of the solvent cannot escape from those areas that contains solute molecules. As a result, vapor pressure is lowered. More heat is needed for the Vapor pressure to reach atmospheric pressure. This principle explains why boiling jam (50% sugar)is hotter than boiling water