Chem-To-Go Lesson 37 Unit 9 COLLIGATIVE PROPERTIES

DEFINITION: a physical property of a solution that differs from the physical property of the solvent due to the presence of the solute particles; the number of solute particles determines the severity of the property’s change BOILING POINT ELEVATION The boiling point of a solution will be higher than the normal boiling point of the solvent. EXAMPLE: Salt water boils at a higher temperature than pure water. FREEZING POINT DEPRESSION The freezing point of a solution will be lower than the normal freezing point of the solvent. EXAMPLE: Salt water freezes at a lower temperature than pure water.

IONIC SOLUTES  Ionic solutes dissociate as they dissolve creating MORE solute particles. COVALENT SOLUTES  Covalent solutes do not dissociate as they dissolve. NUMBER OF SOLUTE PARTICLES

∆T f = K f m i  ∆T f = change in freezing pt.  K f = freezing point constant for the solvent (will be given)  m = molality  i = number of ions present in solute (USE ONLY WITH IONIC SOLUTES) FREEZING POINT DEPRESSION K f of water = 1.86°C/m What is the new freezing point when 15.0g NaCl is dissolved into 200 mL of water?

∆T b = K b m i  ∆T b = change in boiling pt.  K b = boiling point constant for the solvent (will be given)  m = molality  i = number of ions present in solute (USE ONLY WITH IONIC SOLUTES) BOILING POINT ELEVATION K b of water = 0.52°C/m What is the new boiling point when 15.0g NaCl is dissolved into 200 mL of water?

CIVIL ENGINEERING APPLICATION: How many grams of NaCl would need to be added to the water to change the freezing temperature of 200 mL to -8°C? MORE ADVANCED EXAMPLE