2. Properties of Solutions

3. A Solution l A solution is made up of a solute and a solvent. l The solvent does the dissolving. l The solute is the substance that is dissolved. l If a solution is made of two liquids, the one in lesser quantity is the solute.

4. The Universal Solvent l Water is the universal solvent. l Water is a versatile solvent because of its attraction to other molecules and its polarity. l Most of the water on the Earth is not pure, but rather is present in solutions.

5. Water

6. Salt Solutions l Table salt (NaCl), like a great many ionic compounds, is soluble in water. l The salt solution is also an electrolyte, which means its an great conductor of electricity. l This high level of electrical conductivity is always observed when ionic compounds dissolve to a significant extent in water.

7. Salt Solutions l The process by which the charged particles in an ionic solid separate from one another is called dissociation.

8. Salt Solutions

9. l You can represent the process of dissolving and dissociation in shorthand fashion by the following equation.

10. Other Solutions l Water is not only good at dissolving ionic substances. It also is a good solvent for many covalent compounds. l Consider the covalent substance sucrose, commonly known as table sugar, as an example.

11. Like Dissolves Like l Although water dissolves an enormous variety of substances, both ionic and covalent, it does not dissolve everything. l The phrase that scientists often use when predicting solubility is “like dissolves like.”

12. Like Dissolves Like l The expression refers to the polarity of the solute and solvent. l Polar solvents dissolve polar compounds, while l Nonpolar solvents dissolve nonpolar compounds.

13. Making Solutions l A salt dissolves faster if  it is stirred or shaken,  the particles are made smaller, and  the temperature is increased.

14. Making Solutions l In order to dissolve the solvent molecules must come in contact with the solute. l Stirring moves fresh solvent next to the solute. l The solvent touches the surface of the solute. l Smaller pieces increase the amount of surface of the solute.

15. Temperature and Solutions l For solids in liquids, as the temperature goes up the solubility goes up. l A higher temperature makes the molecules of the solvent move around faster and contact the solute harder and more often.

16. Temperature and Solutions l It speeds up dissolving. l Higher temperature usually increases the amount that will dissolve.

17. l How many grams of sodium hydroxide (NaOH) will dissolve in 100 g of water at 15ºC? (100 g)

18. l How many grams of sodium hydroxide will dissolve in 100 g of water at 40ºC? (140 g)

19. l At what temperature will 90 grams of Pb(NO 3 ) 2 dissolve in 100 g of water? (~50 ° C)

20. l At what temperature will 30 grams of KNO 3 dissolve in 100 g of water? (20 ° C)

21. l For gases in a liquid, as the temperature goes up the solubility goes down.

22. l For gases in a liquid, as the pressure goes up the solubility goes up.

23. How Much Solute? l Solubility - The maximum amount of substance that will dissolve at that temperature (usually measured in grams/liter). l If the amount of solute dissolved is less than the maximum that could be dissolved, the solution is called an unsaturated solution.

24. How Much Solute? l A solution which holds the maximum amount of solute per amount of the solution under the given conditions is called a saturated solution.

25. How Much Solute? l A supersaturated solution contains more solute than the usual maximum amount and is unstable. They cannot permanently hold the excess solute in solution and may release it suddenly. l A seed crystal will make the extra come out.

26. How Much? l Generally, a supersaturated solution is formed by dissolving a solute in the solution at an elevated temperature, at which solubility is higher than at room temperature, and then slowly cooling the solution.

27. l If 45 g of KCl is dissolved in 100 g of water at 60ºC, is the solution unsaturated, saturated or supersaturated? (saturated)

28. l If 90 g of Pb(NO 3 ) 2 is dissolved in 100 g of water at 40ºC, is the solution unsaturated, saturated or supersaturated? (supersaturated)

29. l If 30 g of KNO 3 is dissolved in 100 g of water at 20ºC, is the solution unsaturated, saturated or supersaturated? (saturated)

30. l If 10 g of KClO 3 is dissolved in 100 g of water at 50ºC, is the solution unsaturated, saturated or supersaturated? (unsaturated)

31. Liquids l Miscible means that two liquids can dissolve in each other. l Immiscible means they cannot.

32. l Oil and water are immiscible.

33. Measuring Solutions

34. Concentration l Chemists never apply the terms strong and weak to solution concentrations. l Instead, use the terms concentrated and dilute.

35. Concentration l Concentration is a measure of the amount of solute dissolved in a certain amount of solvent. l A concentrated solution has a large amount of solute. l A dilute solution has a small amount of solute.

36. Molarity l For chemistry applications, the concentration term molarity is generally the most useful. l Molarity is the number of moles of solute in 1 Liter of the solution. liter of solution moles of solute M =

37. Molarity l Note that the volume is the total solution volume that results, not the volume of solvent alone. l Suppose you need 1.0 Liter of a 1 M copper (II) sulfate solution.

38. Molarity l STEP 1: Measure a mole of copper (II) sulfate.

39. Molarity l CuSO 4 – Copper: 63.5 g – Sulfur: 32.1 g – Oxygens: 16.0 g x 4 = 64.0 g 159.6 g

40. Molarity l STEP 2: Place the CuSO 4 in a volumetric flask.

41. Molarity l STEP 3: Add some water to dissolve the CuSO 4 and then add enough additional water to bring the total volume of the solution to 1.0 L.

43. Example l What is the molarity of a solution with 2.0 moles of NaCl in 4.0 Liters of solution? M = 4.0 L moles liters 2.0 mol M = 0.50 M

44. Problem l What is the molarity of a solution with 3.0 moles dissolved in 250 mL of solution? M = 0.25 L moles liters 3.0 mol M = 12 M

45. Problem l How many moles of NaCl are needed to make 6.0 L of a 0.75 M NaCl solution? M = 6.0 L moles liters 0.75 M = moles = 4.5 moles

46. Problem l 0.200 moles of NaOH are dissolved in a small amount of water then diluted to 500. mL. What is the concentration? (0.400 M)

47. Problem l How many moles are in 1500 mL of a 3.2 M solution of nitric acid (HNO 3 )? (4.8 mol)

48. Example l 10.3 g of NaCl are dissolved in a small amount of water then diluted to 250 mL. What is the concentration? 58.5 g l NaCl – Sodium: 23.0 g – Chlorine: 35.5 g

49. Example, cont l 10.3 g of NaCl are dissolved in a small amount of water then diluted to 250 mL. What is the concentration? 58.5 g 1 mol10.3 g = 0.176 mol

50. Example, cont. l 10.3 g of NaCl are dissolved in a small amount of water then diluted to 250 mL. What is the concentration? M = 0.25 L moles liters 0.176 mol M = 0.70 M

51. Problem l 80.6 g of KCl are dissolved in a small amount of water then diluted to 500. mL. What is the concentration? (2.16 M)

52. Problem l 125 g of NaC 2 H 3 O 2 are dissolved in a small amount of water then diluted to 750. mL. What is the concentration? (2.03 M)

53. Example l How many grams of CaCl 2 are needed to make 625 mL of a 2.00 M solution? M = 0.625 L moles liters 2.0 M = moles = 1.25 moles

54. Example, cont. l How many grams of CaCl 2 are needed to make 625 mL of a 2.00 M solution? 1 mol 111.1 g1.25 mol = 139 g 139 g of calcium chloride is added to enough distilled water to make a total volume of 625 mL.

55. Problem l How many grams of aluminum nitrate are needed to make 600. mL of a 0.500 M Al(NO 3 ) 2 solution? (45.3 g)

56. l What is the molarity of a KNO 3 solution at 10ºC? (100 g of water = 100 mL of water) (1.88 M)

57. l What is the molarity of a Pb(NO 3 ) 2 solution at 61ºC? (3.02 M)

58. l What is the molarity of a KNO 3 solution at 71ºC? (11.9 M)

59. Dilution Adding Water to a Solution

60. Dilution l Solutions of a needed concentration can be prepared by diluting a concentrated, stock solution. l Solvent is added to the concentrated solution of known volume, but the moles of solute does NOT change! l Therefore: mol concentrated = mol dilute

61. Dilution l mol concentrated = mol dilute l And, mol = M∙V l Therefore: M 1 ∙V 1 = M 2 ∙V 2 l M 1 and V 1 represent the concentration and volume of the concentrated solution. l M 2 and V 2 represent the concentration and volume of the dilute solution.

62. Example l 2.0 L of a 0.88 M solution are diluted to 3.8 L. What is the new molarity? =M1M1 V1V1 M2M2 V2V2 0.88(2.0)3.8 M 2 = 0.46 M

63. Problem l 6.0 L of a 0.55 M solution are diluted to 8.8 L. What is the new molarity? (M 2 = 0.38 M)

64. Problem l You have 150 mL of 6.0 M HCl. What volume of 1.3 M HCl can you make? =M1M1 V1V1 M2M2 V2V2 6.0(150)1.3 V 2 = 690 mL

65. Problem l 6.0 liters of a 0.55 M solution are diluted to a 0.35 M solution. What is the final volume? (V 2 = 9.4 L)

66. Problem l You need 450 mL of 0.15 M NaOH. All you have available is a 2.0 M stock solution of NaOH. How do you make the required solution? =M1M1 V1V1 M2M2 V2V2 0.15(450)2.0 V 2 = 34 mL

67. Problem l You need 450 mL of 0.15 M NaOH. All you have available is a 2.0 M stock solution of NaOH. How do you make the required solution? You should take 34 mL of the 2.0 M NaOH and add (450 – 34) mL = 416 mL of distilled water to the solution.