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CHAPTER 9

CHAPTER 9. Water and Solutions. 9.2 Concentration and Solubility. 9.1 Water Review with Tim and Moby. Check out this video (use your headphones to listen) http://www.brainpop.com/science/earthsystem/water/ Login is “Cavaliers”; password is “jfhs”

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CHAPTER 9

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  1. CHAPTER 9 Water and Solutions 9.2 Concentration and Solubility

  2. 9.1 Water Review with Tim and Moby • Check out this video (use your headphones to listen) • http://www.brainpop.com/science/earthsystem/water/ • Login is “Cavaliers”; password is “jfhs” • You may need to search for the “water” video after logging in • When you’re done, click the quiz link • take the GRADED QUIZ (not the review quiz) • Show me your score on this screen when you’re done for a class grade. • You may take the quiz multiple times to improve your score if needed.

  3. Concentration concentration: the amount of each solute compared to the total solution.

  4. Concentration More solute Less solute

  5. Concentration More solute Less solute How can we express concentration quantitatively (with numbers)?

  6. Concentration There are several ways to express concentration: 1. Mass Concentration

  7. 1. Mass Concentration In a healthy person, potassium is dissolved in blood at a concentration of 140 to 200 mg/L.

  8. 1. Mass Concentration In a healthy person, potassium is dissolved in blood at a concentration of 140 to 200 mg/L. The concentration is expressed as the mass of potassium per volume unit of blood

  9. 1. Mass Concentration In a healthy person, potassium is dissolved in blood at a concentration of 140 to 200 mg/L. If the concentration is less than 130 mg/L:  muscle weakness and heart rhythm instability (hypokalemia) The concentration is expressed as the mass of potassium per volume unit of blood

  10. 1. Mass Concentration In a healthy person, potassium is dissolved in blood at a concentration of 140 to 200 mg/L. If the concentration is less than 130 mg/L:  muscle weakness and heart rhythm instability (hypokalemia) If the concentration is higher than 215 mg/L:  heart instability (hyperkalemia) The concentration is expressed as the mass of potassium per volume unit of blood

  11. Concentration There are several ways to express concentration: 1. Mass Concentration 2. Mass Percent Concentration

  12. 2. Mass Percent Concentration Suppose you dissolve 10.0 g of sugar in 90.0 g of water. What is the mass percent concentration of sugar in the solution?

  13. 2. Mass Percent Concentration Suppose you dissolve 10.0 g of sugar in 90.0 g of water. What is the mass percent concentration of sugar in the solution? Asked: The mass percent concentration Given: 10 g of solute (sugar) and 90 g of solvent (water) Relationships:

  14. 2. Mass Percent Concentration Suppose you dissolve 10.0 g of sugar in 90.0 g of water. What is the mass percent concentration of sugar in the solution? Asked: The mass percent concentration Given: 10 g of solute (sugar) and 90 g of solvent (water) Relationships: Solve:

  15. Concentration There are several ways to express concentration. Here are the 3 ways we use in this class: Mass Concentration Mass Percent Concentration Molar Concentration (Molarity)

  16. 3. Molar Concentration (Molarity) Calculate the molarity of a salt solution made by adding 6.0 g of NaCl to 100 mL of distilled water.

  17. 3. Molar Concentration (Molarity) Calculate the molarity of a salt solution made by adding 6.0 g of NaCl to 100 mL of distilled water. Asked: Molarity of solution Given: Volume of solution = 100.0 mL, mass of solute (NaCl) = 6.0 g Relationships:

  18. 3. Molar Concentration (Molarity) Calculate the molarity of a salt solution made by adding 6.0 g of NaCl to 100 mL of distilled water. Asked: Molarity of solution Given: Volume of solution = 100.0 mL, mass of solute (NaCl) = 6.0 g Relationships: Solve:

  19. 3. Molar Concentration (Molarity) Calculate the molarity of a salt solution made by adding 6.0 g of NaCl to 100 mL of distilled water. Asked: Molarity of solution Given: Volume of solution = 100.0 mL, mass of solute (NaCl) = 6.0 g Relationships: Solve: Answer: 1.03 M solution of NaCl

  20. Solubility What happens when you add 10 g of sugar to 100 mL of water? 10 g sugar 100 mL H2O Conc. (%) = 10 g/110 g

  21. Solubility What happens when you add 10 g of sugar to 100 mL of water? 10 g sugar 100 mL H2O Water molecules dissolve sugar molecules Conc. (%) = 10 g/110 g

  22. Solubility What happens when you add 10 g of sugar to 100 mL of water? But when two sugar molecules find each other, they will become “undissolved” (solid) again…

  23. Solubility What happens when you add 10 g of sugar to 100 mL of water? But when two sugar molecules find each other, they will become “undissolved” (solid) again… … then, they become redissolved in water again.

  24. Solubility What happens when you add 10 g of sugar to 100 mL of water? Equilibrium This is an aqueous equilibrium!

  25. Solubility low Equilibrium “undissolving” dissolving Concentration 10 g sugar 20oC 100 mL H2O Conc. (%) = 10 g/110 g high

  26. “undissolving” dissolving Solubility low Equilibrium Concentration high

  27. “undissolving” dissolving Equilibrium saturation: situation that occurs when the amount of dissolved solute in a solution gets high enough that the rate of “undissolving” matches the rate of dissolving.

  28. Solubility 204 g sugar 20oC 100 mL H2O Conc. = 204 g/100 mL saturation: situation that occurs when the amount of dissolved solute in a solution gets high enough that the rate of “undissolving” matches the rate of dissolving.

  29. “undissolving” dissolving Solubility low 250 g sugar 20oC Undissolved sugar 100 mL H2O Concentration Conc. = 250 g/100 mL Equilibrium high

  30. Temperature and solubility 20oC 30oC 210 g sugar 210 g sugar 100 mL H2O 100 mL H2O Undissolved sugar All the sugar is dissolved

  31. Temperature and solubility 20oC 30oC 210 g sugar 210 g sugar 100 mL H2O 100 mL H2O Undissolved sugar All the sugar is dissolved Temperature has an effect on solubility

  32. solubility: the amount of a solute that will dissolve in a particular solvent at a particular temperature and pressure.

  33. Temperature and solubility You can dissolve (a lot) more sugar at higher temperatures

  34. Temperature and solubility Sugar becomes “undissolved” (solid) as the temperature goes down

  35. Temperature and solubility Temperature does not have the same effect on the solubility of all solutes

  36. Temperature and solubility For some solutes, solubility changes a lot with temperature

  37. Temperature and solubility For other solutes, solubility changes very little with temperature

  38. Temperature affects: - the solubility of solutes how much - the rate of solubility how fast

  39. Dissolving rate Dissolving is a collision process Slow (cold) molecules are not as effective as fast (hot) molecules

  40. Dissolving rate Dissolving is a collision process Slow (cold) molecules are not as effective as fast (hot) molecules Salt dissolves faster in hot water

  41. Dissolving rate Substances are often ground up into powder to make them dissolve faster The same volume has a surface area of 12 cm2 when divided up into smaller cubes A 1 cm cube has a surface area of 6 cm2

  42. The rate of solubility increases: - with an increase in temperature - with an increase in surface area of the solute

  43. Gases are soluble in liquids Dissolved O2 and CO2 allow animal and plant life to exist under water

  44. At higher temperatures: - solid solutes (like salt and sugar) are more soluble - gases are less soluble Solubility of common gases in water at 25oC

  45. Seltzer water is a supersaturated solution of CO2 in water This solution is unstable, and the gas “undissolves” rapidly (bubbles escaping) supersaturation: term used to describe when a solution contains more dissolved solute than it can hold.

  46. Preparing a solution How to prepare a 500.0 mL solution of a 1.0 M CaCl2 solution.

  47. Preparing a solution How to prepare a 500.0 mL solution of a 1.0 M CaCl2 solution. • Determine the formula mass of the solute. Molar mass of CaCl2

  48. Preparing a solution How to prepare a 500.0 mL solution of a 1.0 M CaCl2 solution. • Determine the formula mass of the solute. • Use the formula mass of the solute to determine the grams of solute needed. Molar mass of CaCl2: 110.98 g/mole We need 0.5 moles CaCl2

  49. Preparing a solution How to prepare a 500.0 mL solution of a 1.0 M CaCl2 solution. • Determine the formula mass of the solute. • Use the formula mass of the solute to determine the grams of solute needed. Molar mass of CaCl2: 110.98 g/mole We need 0.5 moles CaCl2 We need 55.49 g CaCl2

  50. Preparing a solution How to prepare a 500.0 mL solution of a 1.0 M CaCl2 solution. • Determine the formula mass of the solute. • Use the formula mass of the solute to determine the grams of solute needed. • Weigh the grams of solute on the balance.

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