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CHAPTER 15

CHAPTER 15. Solutions. Solute. A solute is the dissolved substance in a solution. Salt in salt water. Sugar in soda drinks. Carbon dioxide in soda drinks. Solvent. A solvent is the dissolving medium in a solution. Water in salt water. Water in soda. Concentrated vs. Dilute.

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CHAPTER 15

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  1. CHAPTER 15 Solutions

  2. Solute A solute is the dissolved substance in a solution. Salt in salt water Sugar in soda drinks Carbon dioxide in soda drinks Solvent A solvent is the dissolving medium in a solution. Water in salt water Water in soda

  3. Concentrated vs. Dilute

  4. Saturation of Solutions • A solution that contains the maximum amount of solute that may be dissolved under existing conditions is saturated. • A solution that contains less solute than a saturated solution under existing conditions is unsaturated. • A solution that contains more dissolved solute than a saturated solution under the same conditions is supersaturated.

  5. Saturation and Equilibrium

  6. Solubility Rules Reference Tables

  7. Solubility Values • Solubility of a substance is the amount of that substance required to form a saturated solution with a specific amount of solvent at a specified temperature • The rate at which a substance dissolves does not alter the substances solubility

  8. Factors that Affect Solubility • Temperature • Solubility of solids increases with temperature • Solubility of gases decreases with temperature • Pressure • has no real effect on the solubility of liquids and solids in liquid solvents • Increasing pressure increases the solubility of gases in liquids

  9. Solubility Curves • Each line represents a solute • Higher curves mean that the solute is more soluble, lower curves are less soluble • ABOVE the curve is SUPERsaturated, on the curve is saturated, and UNDER the curve is UNsaturated

  10. Solubility Chart

  11. Solubility Trends • The solubility of MOST solids increases with temperature. • The rate at which solids dissolve increases with increasing surface area of the solid. • The solubility of gases decreases with increases in temperature. • The solubility of gases increases with the pressure above the solution.

  12. Therefore… Solids tend to dissolve best when: • Heated • Stirred • Ground into small particles Gases tend to dissolve best when: • The solution is cold • Pressure is high

  13. Review Questions

  14. Problem 18 A physical change occurs when • A a peach spoils • B a bracelet turns your wrist green • C a copper bowl tarnishes • D a glue gun melts a glue stick

  15. Problem 19 What substance has a melting point of -94°C and a boiling point of 65°C? • a. Ethanol • b. Chlorine • c. Hexane • d. Methanol

  16. Problem 20 22.4 liters of a gas has a mass of 36.5 grams. What is the identity of the gas? • a. Chlorine • b. Hydrogen chloride • c. Nitrogen • d. Hydrogen

  17. Day 2

  18. Molarity and Dilutions

  19. Heat of Solution • The Heat of Solution is the amount of heat energy absorbed (endothermic) or released (exothermic) when a specific amount of solute dissolves in a solvent. • Endothermic: absorbs heat so it feels cool • Exothermic: releases heat so it feels hot

  20. Molarity The concentration of a solution measured in moles of solute per liter of solution. mol of solute= M L of solution

  21. Example What is the molarity of 2.5 mol KCl in 1.0L solution? M= mol L M= 2.5mol 1L M= 2.5M

  22. Example 2 What is the molarity of 0.96g MgCl2 in 500mL of solution? M= mol L 0.96g MgCl2 1mol MgCl2 = .01 mol MgCl2 95g MgCl2 M= .01 mol MgCl2 .500L M= .02M

  23. Example How many moles of solute are contained in 15.25mL of a 2.1M solution of CaCl2? M = mol L # of mol = molarity x L of solution # of mol = 2.1M (.01525L) # of mol = .032 mol CaCl2

  24. Practice Problems

  25. Practice 1 What is the molarity of 1.35 mol H2SO4 in 245mL solution? M= 5.51M

  26. Practice 2 What is the molarity 9.33g Na2S in 450 mL solution? M= 0.27M

  27. Practice 3 How many moles of solute are contained in 125mL of a 0.050M solution of Ba(OH)2? .00625mol

  28. Practice 4 How many grams of solute are contained in 64.3mL of a 0.0238M solution of KOH? .0859g

  29. Practice 5 How many grams of solute are contained in 142mL of a 1.4M solution of K2SO4? 34.6g

  30. Dilutions • Because the # of moles of solute does not change during a dilution Moles of solute in the stock solution = moles of solute after dilution M1V1=M2V2 M1V1 is the molarity and volume of the stock solution and M2V2 is the molarity and volume of the diluted solution

  31. Example • How many milliliters of 2.55M NaOH is needed to make 125ml 0.75M NaOH? M1V1 = M2V2 V1= M2V2 M1 V1=(.75)(125) 2.55 V1= 36.76L

  32. Practice Problems

  33. Practice 1 How would you prepare 500mL of 3 M HCl using 6 M HCl from the stockroom? 250mL

  34. Practice 2 How much 12 M HCl must be used to prepare 500 ml of a 1 M HCl solution? 41.67mL

  35. Homework Molarity and Dilution Problems

  36. Review Questions

  37. Problem 21 • Which of the following substances best illustrates polar covalent bonding? • a. HCl • b. NaBr • c. CsF • d. Cl2

  38. Problem 22 • The methane, CH4, gas molecule exhibits what type of geometric shape? • a. trigonal planar • b. tetrahedral • c. bent or V-shaped • d. trigonal pyramidal

  39. Problem 23 • Which substance would have London dispersion forces as the main type of intermolecular forces of attraction? • a. H2O • b. F2 • c. HCl • d. NaCl

  40. Problem 24 • Which of the following compounds is an exception to the octet rule? • a.BH3 • b.CH4 • c.NH3 • d.H2O

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