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Chapter 13 Water and Its Solutions

Chapter 13 Water and Its Solutions. Surface Tension. The net force acting on the molecules on the surface of some liquids due to the cohesive forces of the molecules Water has a high surface tension. Freezing and Boiling Points. The temperature at which a substances freezes

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Chapter 13 Water and Its Solutions

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  1. Chapter 13 Water and Its Solutions

  2. Surface Tension • The net force acting on the molecules on the surface of some liquids due to the cohesive forces of the molecules • Water has a high surface tension

  3. Freezing and Boiling Points • The temperature at which a substances freezes • The temperature at which a substance boils • Water has a high freezing point and high boiling point

  4. Specific Heat • The energy required to raise the temperature of 1 gram of a substance 1 °C • Water has a high specific heat

  5. Density • Mass/volume • Water is unusual because it is less dense when it freezes

  6. Solubility • The ability for a substance (solute) to dissolve in another substance (solvent) • Solvent – used to dissolve another substance; water is the universal solvent • Solute – the substance that is being dissolved

  7. Factors that affect solubility • Stirring (agitation) • Temperature (Solubility and Temperature) • Surface area (particle size) • Spoon of granulate sugar vs. cube of sugar

  8. Solubility is The ability for a substance (solute) to dissolve in another substance (solvent) Solubility is expressed in mass per volume

  9. Saturated Solution • A solution containing the maximum amount of solute for a given amount of solvent at constant temperature and pressure

  10. Supersaturated Solution • A solution that contains more solute than it can theoretically hold at a given temperature • Excess solute precipitates out of solution

  11. Unsaturated Solution • A solution that contains less solute than a saturated solution at a given temperature and pressure

  12. How can you make a saturated solution unsaturated? Add more solvent; Add more water; dilute the solution

  13. How can you make a saturated solution supersaturated? • Add more solute

  14. Solubility Curve 1. How many grams of KCl can be dissolved at 40°C?

  15. Solubility Curve 2. How many grams of KCl can be dissolved at 80°C?

  16. Solubility Curve 3. At 10°C, 20 grams of KCl is added to 100 grams of water. Is this solution saturated, unsaturated, supersaturated?

  17. Solubility Curve 4. At 10°C, 30 grams of KCl is added to 100 grams of water. Is this solution saturated, unsaturated, supersaturated?

  18. Solubility Curve 5. At 10°C, 50 grams of KCl is added to 100 grams of water. Is this solution saturated, unsaturated, supersaturated?

  19. Solubility Curve 6. Using your answer from #5, how many grams of KCl will settle to the bottom?

  20. Solubility Curve 7. At 10°C, how many grams of KCl are need to make a saturated solution in 200 grams of water?

  21. Solubility Curve 8. At 10°C, how many grams of KCl are need to make a saturated solution in 300 grams of water?

  22.  Generally as the temperature increase the amount of solute ________________ • What is the amount of solute of NH4Cl added at 70 o C? __________________ • What is the amount of solute NaNO3 at 40 o C? ____________________ • NH3 solubility decreases as temperature increases. What is the amount of grams of solute at 90 o C? _____________________

  23. Which solute has the highest solubility at 10 o C? _____________ • Which solute has the lowest solubility at 10 o C? _______________ • Of all the solutes on this graph, which solute is not greatly affected by temperature? _____________________ • Which salt is least soluble in water at 20°C? •  How many grams of potassium chloride can be dissolved in 200 g of water at 80° C?

  24. At 40°c, how much potassium nitrate can be dissolved in 300 g of water? • Which salt shows the least change in solubility from 0-100°C ? • At 30° C,90 g of sodium nitrate is dissolved in 100g of water. Is this solution saturated, unsaturated, or supersaturated?

  25. Molarity • A measure of the "strength" of a solution.  • A solution that we would call "strong" would have a higher molarity than one that we would call "weak." # of moles of soluteMolarity = ----------------------                     Liters of solution • The unit for molarity is M and is read as "molar."   (i.e. 3 M = three molar)

  26. Use the trick to solve for the variables. moles M Liters

  27. Solve for Molarity • What is the molarity of a 5.00 liter solution that was made with 10.0 moles of  KBr ?

  28. Solve for Volume What would be the volume of a 2.00 M solution made with 6.00 moles of LiF?

  29. Solve for Volume •                                 # of moles of soluteLiters of solution =   --------------------                                        Molarity • Given:  # of moles of solute = 6.00 moles           Molarity = 2.00 M (moles/L) • Liters of solution = 6.00 moles                               -----------                               2.00 moles/L • Answer = 3.00 L of solution

  30. Solve for molesIII. Basic molarity problems where the number of moles/grams of solute is the unknown. • How many moles of CaCl2 would be used in the making of 0.500 L of a 5.0M solution?

  31. Use the trick to solve for the variables. moles M Liters

  32. # of moles of solute = Molarity x Liters of solution Given: Molarity = 5.0 M (moles/L)           Volume = 0.500 L # of moles of CaCl2 = 5.0 moles/L x 0.500 moles Answer = 2.5 moles of CaCl2

  33. IV. Given grams instead of moles Convert grams to moles •                      mass given# of moles = -----------------                    Molar mass

  34. Solve for Volume (and convert to moles) What is the volume of 3.0 M solution of NaCl made with 526 g of solute?

  35. Convert to moles Solution: First find the molar mass of NaCl. Na = 23.0 g x 1 = 23.0 gCl = 35.5 g x 1   = 35.5 g                                                 =58.5 g Convert to moles                      mass of sample# of moles = -----------------                      Molar mass                                    526 g# of moles of NaCl = ------------                                   58.5 g Answer:  # of moles of NaCl = 8.99 moles

  36. Example 2.  What is the volume of 3.0 M solution of NaCl made with 526g of solute? Finally, go back to your molarity formula to solve the problem:                               # of moles of soluteLiters of solution =   ------------------------------                                        Molarity Given:  # of moles of solute = 8.99 moles           Molarity of the solution = 3.0 M (moles/L)                                      8.99 moles# of Liters of solution = -------------                                     3.0 moles/L Final Answer = 3.0 L

  37. Solve for moles and then convert to grams • How many grams of CaCl2 would be used in the making 0.500 L of a 5.0M solution?

  38. How many grams of NaI would be used to produce a 2.0 M solution with a volume of 1.00 L? 

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