Chapter 12: Solutions Mrs. Brayfield
12.1: Solutions Solution a homogeneous mixture of two or more substances Solvent the majority component Solute the minority component What is the solute and solvent for salt water? Solute : Solvent:
11.2: Types of Solutions and Solubility A solution may contain any phase of matter but the most common is an aqueous solution This is where water is the solvent and either a solid, liquid, or gas is the solute Remember like dissolves like and if something will dissolve in another we call that being soluble Solubility of a substance is the amount of the substance that will dissolve in a given amount of solvent For example the solubility of sodium chloride in water at 25 C is 36g per 100g of water
Solubility Chemical systems tend to go towards lowering their potential energy (for example bond formation) If we were to put two gases in opposite ends of a container they would spontaneously mix This is NOT because this lowers their potential energy, this is because of entropy Entropy can be used to predict the maximum amount of work which can be obtained from a spontaneous process OR the amount of work required to drive a nonspontaneous process You book defines this as a measure of energy randomness (or disorder) which is wrong More on entropy later
Solubility and Intermolecular Forces Intermolecular forces play a huge role in solutions they determine if something will be miscible (soluble) or not There are three interactions that we need to look at: Solvent-solute interactions Solvent-solvent interactions Solute-solute interactions
Solubility and Intermolecular Forces Table 12.2 Relative Interactions and Solution Formation Solvent-solvent and Solvent-solute > Solution forms solute-solute Solvent-solvent and Solvent-solute = Solution forms solute-solute Solvent-solvent and Solution may or may not form Solvent-solute < solute-solute depending on the difference* Homework Problems: #3, 4, 5
12.3: Energetics of Solution Formation More thermodynamics The enthalpy of solution ( ): ΔH solute is endothermic (+), ΔH solvent is endothermic (+), ΔH mix is exothermic (-)
The Heat of Hydration In many solutions (ionic compounds in water) you can combine the last two terms into one term called the heat of hydration (ΔH hydration ), which is exothermic When the heat of solute is less than the heat of hydration then you get an exothermic reaction When the heat of solute is larger than the heat of hydration that you get an endothermic reaction Also note that for ionic solids ΔH solute = - ΔH lattice Homework Problems: #7, 8
12.4: Solution Equilibrium When a solute dissolves in a solvent there is a dynamic equilibrium (when the rate of dissolution and deposition become equal) When the dissolved solute is in dynamic equilibrium with the undissolved solute we call this a saturated solution When the solution contains less than the equilibrium amount of solute we call this an unsaturated solution When the solution contains more than the equilibrium amount of solute we call this a supersaturated solution
Factors Affecting Solubility There are many factors that affect the solubility of solids: It is highly dependent upon temperature This is why you can dissolve more sugar in warm tea than in cold tea and why cold soda stays bubbly more than warm soda
Factors Affecting Solubility Solubility is also dependent upon pressure The higher the pressure the more soluble a gas is This is why soda cans are pressurized and when you open them the solution bubbles more (less pressure above the solution) Homework Problems: #13, 14, 16
12.5: Solubility Concentration Dilute solution a solution containing small amounts of solute compared to the amount of solvent Concentrated solution a solution containing large amounts of solute compared to the amount of solvent Molarity (M) of a solution is the amount of solute (in moles) divided by the volume of the solution (in liters): This is the most common way to define concentration of a solution and this is the only way you are required to know (more in table 12.5)
Solubility Concentration To properly prepare solutions, you first put your desired amount of solute in a volumetric flask and then add distilled water until the line on the flask has been reached Remember how to do dilutions as well: Where M is molarity and V is volume (this way moles are conserved) Homework Problems: #23, 24, 26, 32, 34 (do only Molarity)
12.6: Colligative Properties A colligative property is a property that depends on the number of particles dissolved in solution, not on the type of particle (there are 4 properties) Vapor pressure lowering When a nonvolatile solute is added to a liquid (pure solvent) to form a solution, the vapor pressure above that solution decreases This is because the solute particles interfere with the ability of the solvent particles to vaporize (they occupy some of the surface area)
Colligative Properties Freezing point depression A solution will have a lower melting point than the pure solvent This is why we put salt on the roads in the winter to lower the freezing point of water so the roads don t form ice Boiling point elevation A solution will have a higher boiling point than the pure solvent This is why cars have antifreeze in them the solution will not boil when cooling an engine
Colligative Properties Osmosis Osmosis is the flow of solvent from a solution of lower solute concentration to one of a higher solution concentration This is why if perfume is sprayed in one corner of the room soon you can smell it in the other corners Homework problem: #42
12.7: Colligative Properties Not responsible for knowing Review problem: #63 http://www.youtube.com/watch?v=9h2f1bjr0p4