Do Now & Announcements Turn in shaving cream lab if you did not do so last class Get Heat HW stamped Answer Heating Curve Questions Today: Solubility Unit 4 Quest next class period: Wed 12/6 (A), Th 12/7 (B) Use last page of midterm review packet as quest review

Review: Solutions Solutions are homogeneous mixtures that may be solid, liquid, or gaseous. If something is not homogeneous (i.e. it is heterogeneous ), it is NOT a solution! Solute vs. Solvent The solute is what is being dissolved. The solvent is what is doing the dissolving

Solubility Solubility= a measure of how much solute will dissolve in a certain amount of solvent

Factors that Affect Solubility Temperature—Solid Solutes: IN GENERAL As the temperature ↑, the solubility of a SOLID solute in a liquid solvent ↑ At a higher temperature, you can dissolve more solute in the same amount of solvent

Temperature: Gas Solutes As the temperature ↑, the solubility of a GAS solute in a liquid solvent ↓ At a higher temperature, you can dissolve less solute in the same amount of solvent

Factors that Affect Solubility: Pressure Solids & Liquids: Not much of an effect on solubility Gases: As the pressure ↑, the solubility of a GAS solute in a liquid solvent ↑ At a higher pressure, you can dissolve more solute in the same amount of solvent

Consider the terms unsaturated and saturated 1. Which term applies to a sponge that is dry? 2. Which term applies to a sponge that is soaked?   3. Can you add more water to a sponge that is already soaked?

SATURATED UNSATURATED SUPERSATURATED SUPERSATURATED SATURATED

How do you make a supersaturated solution? Heat up solvent (water) first Then add solute so that it is completely saturated Allow your solution to cool.

Why do you think people pour salt on the roads/sidewalks in the winter? Why do you think people add salt to water when making pasta?

Colligative Properties The addition of a solute to a solvent causes the boiling point of the solvent to increase . This phenomenon is known as boiling point elevation The addition of a solute to a solvent causes the freezing point of the solvent to decrease. This phenomenon is known as freezing point depression The higher the concentration of solute particles, the greater the effect.

Why does this happen? When a solute is dissolved in a solvent, the vapor pressure of the resulting solution will be lower than the vapor pressure of the pure solvent. When a solvent is pure, its particles occupy the entire surface area. However, when a solute is added, a mix of solvent and solute particles occupy the surface area. With fewer solvent particles at the surface, fewer particles enter the gaseous state, and the vapor pressure is lowered.

Recall that boiling occurs when the vapor pressure from the surface of the liquid is equal to the air pressure pushing down on the surface. If adding a solute lowers the vapor pressure, the solution must be heated to a higher temperature in order to make VP = AP

Freezing: the solute particles get in the way of the pure substances ability to form a solid structure (i.e. water forming ice crystals)