Notes on Colligative Properties Mr Keith Freezing Point

Notes on Colligative Properties Mr. Keith

Freezing Point Depression Turn to your neighbor and explain why Penn. DOT puts salt down on the roads when it snows Why?

Boiling Point Elevation Turn to your neighbor and explain why chefs put salt in water to boil the water when cooking. http: //www. chem. purdue. edu/gchelp/solutions/eboil. h tml

What are colligative properties? Properties that are affected only by the number of particles dissolved in the solution The identity of the particles is not important, only the number What temperature does water boil? What temperature does water freeze?

Molality NOT THE SAME THING AS MOLARITY!!!! Equation: moles of solute/kilograms of solvent Find moles just like you normally would Note: it is in kilograms, or kg of solvent Solvent, not solution

Example What is the molality of a solution containing 12 grams of salt (Na. Cl) dissolved in 2 liters of water? m= mol solute/kg solvent

Boiling point elevation ΔT = Kb (m) i ΔT = change in temperature Kb is a boiling point elevation constant specific to a substancem is the molality, remember it is not molarity. i is the vant’ off factor. (how many particles it breaks into) Another way to write this is ΔT = Kb (mol/kg solvent) i

Freezing point depression ΔT = Kf (m) i ΔT = change in temperature Kf is the freezing point depression constant m is the molality, remember it is not molarity. i is the vant’ off factor. If it is not given, assume it to equal 1. Another way to write this is ΔT = Kf (mol/kg solvent) i

On the test…. . SI Units (mass=grams, volume = liters, time, etc) Metric Unit Prefixes ( kilo-micro) Converting between metric units Sig Figs Measuring Instruments Factor Label Method (Fence Posting) Know how to convert between…. Mass and moles Moles and particles Moles and volume of a solution Dilution Molar highway Freezing point depression and boiling point elevation (Colligative properties) Look over powerpoint. Solutions (saturated, super saturated, unsaturated) solute, solvent, etc.