CHAPTER 16-SOLUTIONS

1. CHAPTER 16-SOLUTIONS

2. Solutions The substance there is the most of is typically the solvent! Homogeneous mixtures that may be solid, liquid or gaseous • Solute: The part of the solution that is dissolved • Solvent: The part of the solution that does the dissolving Water is known as the universal solvent

3. Rate of Solution • Stirring: Speeds up the rate of solution • Fresh solvent is continually brought into contact with the surface of the solute • Temperature: Higher temperature leads to higher rate of solutions • Particles move faster which brings the solute & solvent together more quickly

4. Rate of Solution • Particle Size: More surface area leads to a faster rate of solution • Powdered sugar dissolves faster than a sugar cube

5. SOLUBILITY The amount of solute that dissolves in a given quantity of a solvent at a specified temperature and pressure to produce a saturated solution Unit: grams of solute per 100 g of solvent g solute/100 g solvent

6. SATURATED SOLUTION • Contains the maximum amount of solute for a given quantity of solvent at a constant temperature and pressure • If additional solute is added to a saturated solution, it will not dissolve • At a state of dynamic equilibrium; the rate of solution equals the rate of dissolution

7. UNSATURATED SOLUTION • A solution that contains less solute than a saturated solution at a given temperature and pressure • If additional solute is added to an unsaturated solution, the solute will dissolve until the solution is saturated.

8. SUPERSATURATED SOLUTION A solution that contains more solute than it can theoretically hold at a given temperature • If solute is added to a supersaturated solution, the crystal will increase in size as more solute precipitates out of solution

9. Miscible: Two liquids that will dissolve in each other in all proportions • Any amount of the liquids will dissolve • Example: Ethanol & Water • Immiscible: Liquids that are insoluble in one another • Example: Oil & Vinegar

10. FACTORS AFFECTING SOLUBILITY • Temperature • The solubility of most solids increases as the temperature of the solvent increases • The solubility of most gases is greater as the temperature of the solvent decreases

11. FACTORS AFFECTING SOLUBILITY Pressure: • Does not effect solid or liquid solubility • Gas solubility increases as the partial pressure of the gas above the solution increases Henry’s Law: At a given temperature, the solubility(S) of a gas in a liquid is directly proportional to the pressure (P) of the gas above the liquid S1= S2 P1 P2

12. SOLUBILITY QUESTIONS • What happens to the solubility of KNO3 as the temperature increases? • 50 g of KNO3 is dissolved in 100 g of water at 30ºC. Is this a saturated, unsaturated or supersaturated solution? • 20 g of KNO3 is dissolved in 100 g of water at 60ºC. Is this a saturated, unsaturated or supersaturated solution? • How much KNO3 will dissolve at 50ºC? • How much KNO3 will crystallize if the temperature is lowered from 40ºC to 10ºC? • A saturated solution of KNO3 is prepared in 100 g of water at 30ºC. If the solution is heated to 70ºC, how much more KNO3 must be added to obtain a saturated solution? SOLUBILITY CURVES Graph that illustrates the grams of solute that dissolves in 100 g of water at a given temperature • The Line: A saturated solution (# of grams that can dissolve in 100 g water at that temperature) • Above the line: A supersaturated solution • Below the line: An unsaturated solution

13. Which substance shows a decrease in solubility as temperature increases? • Which substance exhibits the least change in solubility? • Which compound is most soluble at 10ºC? • Which compound is least soluble at 50ºC? • Assuming no supersaturation, how many grams of K2Cr2O7 crystallizes if a warm solution containing 50 g of K2Cr2O7 in 100 g of water is cooled to 10ºC?

14. The concentration is a measure of the amount of solute that is dissolved in a given quantity of solvent • Dilute Solution: One that contains a small amount of solute • Concentrated Solution: One that contains a large amount of solute

15. Molarity (M) The number of moles of solute dissolved in 1 Liter of solution Molarity (M) = moles of solute liters of solution Examples: • A solution has a volume of 2.0 L and contains 36.0 g of glucose (C6H12O6). What is the molarity of this solution? 2) How many grams of calcium chloride are needed to make 250 mL of a 2.0 M solution of calcium chloride?

16. DILUTING A SOLUTION M1V1 = M2V2M = Molarity, V = Volume Examples: • How many milliliters of aqueous 2.00 M MgSO4 solution must be diluted with water to prepare 100.0 mL of aqueous 0.400 M MgSO4? • How could you prepare 250 mL of 0.20 M NaCl using only a solution of 1.0 M NaCl and water?

17. PERCENT SOLUTION Another way to express the concentration of a solution • As the ratio of the volume of the solute to the volume of the solution % by Volume = Volume of Solute x 100% Volume of Solution • As the ratio of the mass of the solute to the mass of the solution % by Mass = Mass of Solute x 100% Mass of Solution

18. PERCENT SOLUTION EXAMPLES • What is the percent volume of ethanol (C2H6O, or ethyl alcohol) in the final solution when 85 mL of ethanol is diluted to a volume of 250 mL with water? • A bottle of the antiseptic hydrogen peroxide (H2O2) is labeled 3.0% volume. How many mL H2O2 are in a 400.0 mL bottle of this solution? • Suppose you want to make 2000 g of solution of glucose in water that has a 2.8% by mass concentration of glucose. How much glucose should you use?

19. MOLARITY Example: A solution has a volume of 2.0 L and contains 0.36 mol of glucose (C6H12O6). What is the molarity of the solution? Example: Mass of Kool-Aid needed for 0.1 M solution?