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Chapter 14 Solutions

Chapter 14 Solutions. What are solutions?. A Solution is…. What are solutions?. Solution: a uniform mixture that contains 2 or more substances (solids, liquids, or gases); also called a homogeneous mixture. What are solutions?.

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Chapter 14 Solutions

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  1. Chapter 14Solutions

  2. What are solutions? A Solution is…

  3. What are solutions? Solution: a uniform mixture that contains 2 or more substances (solids, liquids, or gases); also called a homogeneous mixture

  4. What are solutions? Solution: a uniform mixture that contains 2 or more substances (solids, liquids, or gases); also called a homogeneous mixture Solute: Solvent:

  5. What are solutions? Solution: a uniform mixture that contains 2 or more substances (solids, liquids, or gases); also called a homogeneous mixture Solute: substance that gets dissolved Solvent: dissolving medium Example: salt water - salt is solute - water is solvent

  6. What are solutions? What are some solutions that you use in everyday life?

  7. Characteristics of Solutions Soluble vs Insoluble

  8. Characteristics of Solutions Soluble vs Insoluble dissolves in solvent does NOT dissolve in solvent *** Like Dissolves Like ***

  9. Soluble OR Insoluble Sand in water Oil in vinegar Vinegar in water Melted butter in oil Carbon dioxide (g) in water Chocolate syrup in milk

  10. Solvation in aqueous solutions Why are some substances soluble in one solvent but not another?

  11. Solvation in aqueous solutions Why are some substances soluble in one solvent but not another? * It has to do with attractive forces between particles: 1. forces between pure solute particles 2. forces between pure solvent particles 3. forces between solute and solvent particles

  12. Attractive Forces & Solvation To dissolve a solute in a solvent: • If the attractive forces between solute & solvent are greater than forces holding solute together → the solvent will pull apart the solute, and dissolve it (“solvation”) • If the attractive forces between solute & solvent are smaller than attractive forces holding solute together → the solvent will NOT pull apart the solute.

  13. Aq. Solutions of ionic compounds Dissolving a solute (NaCl) in water: • Charged ends of water attract + and - ions in crystal. • Attraction between dipoles (in water) & ions is greater than attraction of ions within the crystal • So, crystal dissolves in water

  14. Aq. Solutions of ionic compounds Dissolving CaSO4 in water: • Attractive forces between Ca2+ and SO42- are so strong compared to attractive forces between water & ions. • Calcium sulfate does NOT dissolve in water • “Hard Water” stains

  15. Aq. solutions of molecular compounds Dissolving sugar in water: • O-H bond in sugar becomes site for hydrogen-bonding with water molecules • Strong attractive forces between water & sugar are stronger than those in sugar alone; sugar dissolves.

  16. Factors that affect rate of solvation Solvation can only occur when solute and solvent are in contact with each other. Three common ways to increase collisions between solute & solvent: Agitating mixture Increasing surface area of solute (smaller particles) Increasing temperature of solvent

  17. Heat of Solution • Energy is released or absorbed during the solvation process. • Energy is required to overcome attractive forces within solute and within solvent…endothermic. • Energy is released when solute and solvent particles mix (particles attract each other)…exothermic. • Overall energy change during the formation of a solution is call the heat of solution.

  18. Solubility • Every solute has a characteristic solubility in a given amount of solvent at a specified temperature and pressure. • High solubility = more solute can be dissolved • Low solubility = less solute can be dissolved

  19. Factors that affect Solubility • Temperature: most solutes are more soluble at higher temperatures. • Pressure (gaseous solutes and solutions) • Nature of solute and solvent (high or low attractive forces between solute and solvent; compared to attractive forces with solute alone)

  20. Solubility & Temperature Solubility of some solutes in water (g/100 g H2O) *Most soluble? *Least soluble? *Solubilities affected by temperature?

  21. Saturated, unsaturated, supersaturated Contains more solute that a saturated solution at the same temperature Contains less dissolved solute for a given T & P. Contains the maximum amount of dissolved solute for a given T & P. Saturated solution Unsaturated solution Supersaturated solution

  22. Solubility & Pressure • Solubility of gases increases as external pressure (pressure above solution) increases. • Carbonated beverages contain carbon dioxide dissolved in aqueous solution; results in the “fizz”. • If container is left open, the CO2 will escape, resulting in “flat” soda.

  23. Henry’s Law • Henry’s Law: solubility (S) of a gas in a liquid is directly proportional to the pressure (P) of the gas above the liquid, at a given T. • S1 = S2 • P1 P2 • S1: solubility of gas at pressure P1 • S2: solubility of gas at new pressure P2

  24. Practice Problem If 0.85 g of a gas at 4.0 atm of pressure dissolves in 1.0 L of water at 25 °C, how much will dissolve in 1.0 L of water at 1.0 atm of pressure and the same temperature?

  25. Practice Problem If 0.85 g of a gas at 4.0 atm of pressure dissolves in 1.0 L of water at 25 °C, how much will dissolve in 1.0 L of water at 1.0 atm of pressure and the same temperature? Hint: Solubility has units of g solute/L solvent

  26. Practice Problem If 0.85 g of a gas at 4.0 atm of pressure dissolves in 1.0 L of water at 25 °C, how much will dissolve in 1.0 L of water at 1.0 atm of pressure and the same temperature? S1 = 0.85 g/1.0 L = 0.85 g/L

  27. Practice Problem If 0.85 g of a gas at 4.0 atm of pressure dissolves in 1.0 L of water at 25 °C, how much will dissolve in 1.0 L of water at 1.0 atm of pressure and the same temperature? S1 = 0.85 g/L S2 = ? P1 = 4.0 atm P2 = 1.0 atm

  28. Practice Problem If 0.85 g of a gas at 4.0 atm of pressure dissolves in 1.0 L of water at 25 °C, how much will dissolve in 1.0 L of water at 1.0 atm of pressure and the same temperature? Known: S1 = S2 P1 P2 Unknown:

  29. Practice Problem If 0.85 g of a gas at 4.0 atm of pressure dissolves in 1.0 L of water at 25 °C, how much will dissolve in 1.0 L of water at 1.0 atm of pressure and the same temperature? S2 = (S1)(P2) (P1)

  30. Practice Problem If 0.85 g of a gas at 4.0 atm of pressure dissolves in 1.0 L of water at 25 °C, how much will dissolve in 1.0 L of water at 1.0 atm of pressure and the same temperature? S2 = (S1)(P2) (P1) S2 = (0.85 g/L)(1.0 atm) = 0.21 g/L (4.0 atm)

  31. 15.2 Solution Concentration Concentration: a measure of how much solute is dissolved in a specific amount of solvent or solution. Qualitatively: think in terms of “concentrated” or “dilute”. Which one is dilute? Concentrated?

  32. Expressing Solution Concentration As a chemist, we want quantitative descriptions! (Want an actual number…How much?) Concentration can be represented by: percent by mass or volume Molarity Molality Mole fraction

  33. Concentration Ratios

  34. Percent by Mass & Concentration Percent by Mass: relates mass of solute to mass of solution. Percent by Mass = x 100 * mass of solution = mass solute + mass solvent

  35. Example: Percent by mass What is the percent by mass of NaCl, if 3.6 g NaCl is added to 100.0 g water?

  36. Example: Percent by mass What is the percent by mass of NaCl, if 3.6 g NaCl is added to 100.0 g water? Percent by Mass = x 100

  37. Example: Percent by mass What is the percent by mass of NaCl, if 3.6 g NaCl is added to 100.0 g water? Percent by Mass = x 100 mass of solute: mass of solution:

  38. Example: Percent by mass What is the percent by mass of NaCl, if 3.6 g NaCl is added to 100.0 g water? Percent by Mass = x 100 mass of solute: 3.6 g mass of solution: (3.6 g + 100.0 g) = 103.6 g

  39. Example: Percent by mass What is the percent by mass of NaCl, if 3.6 g NaCl is added to 100.0 g water? Percent by Mass = x 100 Percent by Mass = 3.5 % NaCl

  40. Example: Percent by mass What is the percent by mass of NaHCO3 in a solution containing 20 g NaHCO3 dissolved in 600 mL H2O?

  41. Example: Percent by mass Example: Percent by mass What is the percent by mass of NaHCO3 in a solution containing 20 g NaHCO3 dissolved in 600 mL H2O? Percent by Mass = x 100 What is the percent by mass of NaHCO3 in a solution containing 20 g NaHCO3 dissolved in 600 mL H2O?

  42. Example: Percent by mass What is the percent by mass of NaHCO3 in a solution containing 20 g NaHCO3 dissolved in 600 mL H2O? Percent by Mass = x 100 mass of solute: 20 g mass of solutions: ?

  43. Example: Percent by mass What is the percent by mass of NaHCO3 in a solution containing 20 g NaHCO3 dissolved in 600 mL H2O? ** We need to convert 600 mL water to grams water

  44. Example: Percent by mass What is the percent by mass of NaHCO3 in a solution containing 20 g NaHCO3 dissolved in 600 mL H2O? ** We need to convert 600 mL water to grams water ** 1 mL H2O = 1 g H2O ** So… 600 mL = 600 g

  45. Example: Percent by mass What is the percent by mass of NaHCO3 in a solution containing 20 g NaHCO3 dissolved in 600 mL H2O? Percent by Mass = x 100 mass of solute: 20 g mass of solutions: (20 g + 600 g) = 620 g

  46. Example: Percent by mass What is the percent by mass of NaHCO3 in a solution containing 20 g NaHCO3 dissolved in 600 mL H2O? Percent by Mass = x 100

  47. Example: Percent by mass What is the percent by mass of NaHCO3 in a solution containing 20 g NaHCO3 dissolved in 600 mL H2O? Percent by Mass = x 100 = 3.2 %

  48. Percent by Volume & Concentration Percent by Volume: used to describe solution, when both solute and solvent are liquids. Percent by Volume = x 100 * volume of soln = volume solute + volume solvent

  49. Example: Percent by Volume What is the percent by volume of ethanol in a solution that contains 35 mL of ethanol dissolved in 115 mL water?

  50. Example: Percent by Volume What is the percent by volume of ethanol in a solution that contains 35 mL of ethanol dissolved in 115 mL water? Percent by Volume = x 100

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