Colligative Properties of Solutions

Vapor Pressure Lowering Colligative property – A property that depends only on the number of solute particles and not their identity. Three important colligative properties are: 1.) Vapor pressure lowering 2.) Boiling point elevation 3.) Freezing point depression

Vapor Pressure Lowering Continued The decrease in a solution’s vapor pressure is proportional to the number of particles the solute makes in solution. List the following in order of decreasing vapor pressure: Three moles of aqueous: CaCl2, C6H12O6, NaCl. C6H12O6  NaCl  CaCl2 This is because as the compounds above dissolve in water, glucose doesn’t dissociate into it’s constituent elements, sodium chloride dissociates into 2 ions, and calcium chloride dissociates into 3 ions.

Freezing Point Depression Freezing point depression – the difference in temperature between the freezing point of a solution and the freezing point of a pure solvent. What is lower, the freezing point of a solution, or a pure solvent? The freezing point of a solution is lower than a pure solvent because a solute disrupts the freezing pattern.

Freezing Point Depression (Continued) The magnitude of the freezing point depression is proportional to the number of solute particles dissolved in solvent and does not depend on their identity. If the addition of one mole of solute to 1000 g of water lowers the freezing point by 1.86oC, at what temperature would water freeze if one mole of the following were added: Glucose, NaCl, CaCl2. Why? Glucose: -1.86oC NaCl: -3.72oC CaCl2:-5.58oC

Boiling Point Elevation Boiling Point Elevation – The difference in temperature between the boiling point of a solution and the boiling point of the pure solvent. The magnitude of boiling point elevation is proportional to the number of solute particles dissolved in the solvent. The boiling point of water increases by 0.512oC for every mole of particles that the solute forms when dissolved in 1000 g of water.

16.3 pg. 537 #'s 28, 31, 32 Study for Quiz Chapter 16