1. 1 Why do we do that? we spread salt on icy roads and walkways to melt the ice we add antifreeze to car radiators to prevent the water from boiling or freezing antifreeze is mainly ethylene glycol when we add solutes to water, it changes the freezing point and boiling point of the water

2. 2 Colligative Properties the properties of the solution are different from the properties of the solvent any property of a solution whose value depends only on the number of dissolved solute particles is called a colligative property it does not depend on what the solute particle is the freezing point, boiling point and osmotic pressure of a solution are colligative properties

3. 3 Solution Concentration Molality, m moles of solute per 1 kilogram of solvent defined in terms of amount of solvent, not solution does not vary with temperature  because based on masses, not volumes mass of solution = mass of solute + mass of solvent mass of solution = volume of solution x density

4. 4 Example: Calculate the molality of a solution containing 17.2 g of ethylene glycol (C 2 H 6 O 2 ) dissolved in 0.500 kg of water.

5. 5 Freezing Points of Solutions the freezing point of a solution is always lower than the freezing point of a pure solvent Freezing Point Depression the difference between the freezing points of the solution and pure solvent is directly proportional to the molal concentration  T f = m x K f K f = freezing point constant used to determined molar mass of compounds

6. 6 Freezing & Boiling Point Constants

7. 7 Example: Calculate the freezing point of a 1.7 m ethylene glycol solution.

8. 8 Example: Calculate the boiling point of a 1.7 m ethylene glycol solution.

9. 9 Colligative Properties of Electrolytes Since these properties depend on the number of particles dissolved, solutions of electrolytes (which dissociate in solution) should show greater changes than those of nonelectrolytes.

10. 10 Osmosis & Osmotic Pressure osmosis is the process in which solvent molecules pass through a semi-permeable membrane that does not allow solute particles to pass solvent flows to try to equalize concentration of solute on both sides solvent flows from side of low concentration to high concentration osmotic pressure is pressure that is needed to prevent osmotic flow of solvent isotonic, hypotonic and hypertonic solutions hemolysis

11. 11 Drinking Seawater Because seawater has a higher salt concentration than your cells, water flows out of your cells into the seawater to try to decrease its salt concentration. The net result is that, instead of quenching your thirst, you become dehydrated.

12. 12 Osmotic Pressure Solvent flows through a semipermeable membrane to make the solution concentration equal on both sides of the membrane. The pressure required to stop this process is the osmotic pressure.

13. 13 Molar Mass from Colligative Properties We can use the effects of a colligative property such as osmotic pressure to determine the molar mass of a compound.

14. 14 Osmosis in Blood Cells If the solute concentration outside the cell is greater than that inside the cell, the solution is hypertonic. Water will flow out of the cell, and crenation results.

15. 15 Osmosis in Cells If the solute concentration outside the cell is less than that inside the cell, the solution is hypotonic. Water will flow into the cell, and hemolysis results.

16. 16 Hemolysis & Crenation normal red blood cell in an isotonic solution red blood cell in hypotonic solution – water flows into the cell – eventually causing the cell to burst red blood cell in hypertonic solution – water flows out of the cell – eventually causing the cell to distort and shrink

17. 17 Rate of Dissolving What are three ways that you can increase the rate at which a solid solute dissolves in a solvent? 1. 2. 3.

18. 18 Tyndall Effect Colloidal suspensions can scatter rays of light. This phenomenon is known as the Tyndall effect.