1. Water and Solutions

2. Water and its properties Objectives: 1. Explain surface tension 2. Describe the structure of ice and liquid water.

3. Water in the liquid state: Water is a polar molecule. ++ H2OH2O 

4. Hydrogen bonding: the negative end of the water molecule is attracted to the positive ends of other molecules- resulting in hydrogen bonding. O H H Hydrogen bond  

6. Copyright © 2007 Pearson Benjamin Cummings. All rights reserved. Water molecules “stick” together to create surface tension to support light weight objects. It also tends to hold a drop of a liquid in a spherical shape. Surfactants interfere with hydrogen bonding reducing surface tension. This attraction between water molecules slows the tendency of water evaporation.

7. Water in solid state: Solid ice is less dense than liquid water, thus it floats, making it one of the few solids that floats on its own liquid. Why? Hydrogen bonds hold the water molecules in place in the solid phase, when ice melts, the water molecules pack closer together making liquid water more dense. This is important for organisms living in a pond. A layer of ice on the top of a pond prevents water beneath to freeze completely. Classwork: surfactants activity

8. Heterogeneous systems Objectives: 1. Distinguish between a suspension and a solution 2. Identify the characteristics of a colloid.

9. Suspensions: a mixture from which particles settle out upon standing. Have very large particles Can be filtered Ex. Muddy water some medicines (antibiotics)

10. Colloids Have medium sized particles Can not be filtered. Many colloids are cloudy or milky in appearance. Show Tyndall effect (the path of light is visible)

11. Types of colloids Colloid typeDispersion medium Dispersed substance Examples AerosolGasLiquid AerosolGasSolid LiquidGas Liquid Solid Gas Solid emulsion SolidLiquid Solid

12. Classwork: Complete the table on the last slide, giving examples for the different types of colloids.

13. Solutions Objectives: Distinguish between a solvent and a solute Describe what happens in the solution process Explain what electrolytes are.

14. Definitions Solution - Solution - homogeneous mixture Solvent Solvent - present in greater amount Solute Solute - substance being dissolved

15. Solution = Solute + Solvent Solute - gets dissolved Solvent- does the dissolving Aqueous(water) Tincture(alcohol) Amalgam(mercury) Organic Polar Non-polar Dental filling

16. Types of Solutions SoluteSolventSolution Gaseous Solutions gas liquid gas air (nitrogen, oxygen, argon gases) humid air (water vapor in air) Liquid Solutions gas liquid solid liquid carbonated drinks (CO 2 in water) vinegar (CH 3 COOH in water) salt water (NaCl in water) Solid Solutions liquid solid dental amalgam (Hg in Ag) sterling silver (Cu in Ag), alloys Charles H.Corwin, Introductory Chemistry 2005, page 369

17. Dissolving Process In order to dissolve - the solvent molecules must come in contact with the solute. Stirring moves fresh solvent next to the solute. The solvent touches the surface of the solute. Smaller pieces increase the amount of surface of the solute.

18. Solvation Solvation – Solvation – the process of dissolving: solute particles are separated and pulled into solution solute particles are surrounded by solvent particles

19. Dissolving of NaCl Timberlake, Chemistry 7 th Edition, page 287 HH O Na + + - - + - + + - Cl - + - + hydrated ions

20. Dissolving of Salt in Water NaCl(s) + H 2 O  Na + (aq) + Cl - (aq) Cl - ions Na + ions Water molecules

21. Dissolving of Salt in Water NaCl(s) + H 2 O  Na + (aq) + Cl - (aq)

22. Pure water does not conduct an electric current Zumdahl, Zumdahl, DeCoste, World of Chemistry  2002, page 215 Source of electric power Pure water

23. Ionic Solutions conduct a Current Zumdahl, Zumdahl, DeCoste, World of Chemistry  2002, page 215 Source of electric power Free ions present in water

24. Electrolytes Copyright © 2007 Pearson Benjamin Cummings. All rights reserved. (a) Nonelectrolyte (b) Weak electrolyte (c) Strong electrolyte

25. Electrolytes Timberlake, Chemistry 7 th Edition, page 290 Electrolytes Electrolytes - solutions that carry an electric current NaCl(aq) Na + + Cl - HF(aq) H + + F - strong electrolyteweak electrolytenonelectrolyte

26. Electrolyte Imbalances ElectrolyteNormal range (mmol / L) ExcessDefiency Sodium Na + 135 - 145 Hypernatremia (increased urine excretion; excess water loss) Hyponatremia (dehydration; diabetes- related low blood pH; vomiting, diarrhea) Potassium K + 3.5 – 5.0 Hyperkalemia (renal failure, low blood pH) Hypokalemia (gastointestinal conditions) Hydrogen carbonate HCO 3 - 24 - 30 Hypercapina (high blood pH; hypoventilation) Hypocapnia (low blood pH; hyper- ventilation; dehydration) Chloride Cl - 100 - 106 Hyperchloremia (anemia, heart conditions, dehydration) Hypochloremia (acute infections; burns; hypoventilation)

27. Copyright © 2007 Pearson Benjamin Cummings. All rights reserved. (a) Cells in dilute salt solution (b) Cells in distilled water(c) Cells in concentrated salt solution IsotonicHypotonicHypertonic

28. Classwork: go to my wiki Read article “The Quest for a Clean Drink” Answer the questions. Webquest

29. Properties of Solutions OBJECTIVES: Identify the factors that determine the rate at which a solute dissolves. Identify the factors that determine the mass of solute that will dissolve in a given mass of solvent.

30. Solution formation The “nature” (polarity, or composition) of the solute and the solvent will determine… 1. Whether a substance will dissolve 2. How much will dissolve Factors determining rate of solution... 1. stirring (agitation) 2. surface area the dissolving particles 3. temperature

31. 1. Stirring (agitation) moves fresh solvent into contact with the solute. 2. Smaller pieces increases the amount of surface area of the solute. 3. Higher temperature makes the molecules of the solvent move faster and contact the solute harder and more often. –Speeds up dissolving. Higher Temperature ALSO Usually increases the amount that will dissolve (an exception is gases ).

32. Solubility- is the maximum amount of substance that will dissolve at a specific temperature. The units for solubility are: grams of solute/100 grams solvent 1) Saturated solution- Contains the maximum amount of solute dissolved. NaCl = 36.0 g/100 mL water 2) Unsaturated solution- Can still dissolve more solute (for example 28.0 grams of NaCl/100 mL) 3) Supersaturated- solution that is holding (or dissolving) more than it theoretically can; a “seed crystal” will make it crystallize. Very unstable.

33. Solubility SATURATED SOLUTION no more solute dissolves UNSATURATED SOLUTION more solute dissolves SUPERSATURATED SOLUTION becomes unstable, crystals form increasing concentration

34. a. The solubility of the KNO 3 increases as the temperature increases. b. Yb 2 (SO 4 ) 3 shows a decrease in solubility as the temperature increases, and NaCl shows the least change in solubility as temperature changes. c. Only a negligible amount of NaCl would go into solution, if any.

35. Solubility Table LeMay Jr, Beall, Robblee, Brower, Chemistry Connections to Our Changing World, 1996, page 517 0 10 20 30 40 50 60 70 80 90 100 Solubility vs. Temperature for Solids Solubility (grams of solute/100 g H 2 O) KI KCl 20 10 30 40 50 60 70 80 90 110 120 130 140 100 NaNO 3 KNO 3 HClNH 4 Cl NH 3 NaCl KClO 3 SO 2 shows the dependence of solubility on temperature gases solids

36. LeMay Jr, Beall, Robblee, Brower, Chemistry Connections to Our Changing World, 1996, page 517 0 10 20 30 40 50 60 70 80 90 100 Solubility vs. Temperature for Solids Solubility (grams of solute/100 g H 2 O) KI KCl 20 10 30 40 50 60 70 80 90 110 120 130 140 100 NaNO 3 KNO 3 HClNH 4 Cl NH 3 NaCl KClO 3 SO 2 gases solids a) 80g NaNO 3 at 45  C. The solution is ? unsaturated b) 100g NaNO 3 at 45  C. The solution is ? c) 120g NaNO 3 at 45  C. The solution is ? d) How much more NaNO 3 can you add to a solution with 40g of NaNO 3 at 45  C until it becomes saturated? saturated supersaturated 60 g

37. Liquids Miscible means that two liquids can dissolve in each other water and antifreeze water and ethanol Partially miscible- slightly water and ether Immiscible means they can’t oil and vinegar

38. Solids tend to dissolve best when: They are heated They are stirred Crushed into smaller particles Gases tend to dissolve best when: The solution is cold The pressure is high

39. For solids in liquids, as the temperature goes up-the solubility usually goes up For gases in a liquid, the effect is the opposite of solids in liquids As the temperature goes up, gas solubility goes down Think of boiling water bubbling? Thermal pollution may result from industry using water for cooling Solids dissolved in liquids Gases dissolved in liquids ToTo Sol. ToTo As T o, solubility

40. Solutions video Classwork: solubility graph handout

41. Concentration of Solutions Objectives: 1. Solve problems involving the molarity of a solution. 2. Describe the effect of dilution on the total moles of solute in solution. 3. Define percent by volume and percent by mass solutions.

42. Concentration is... a measure of the amount of solute dissolved in a given quantity of solvent A concentrated solution has a large amount of solute A dilute solution has a small amount of solute These are qualitative descriptions But, there are ways to express solution concentration quantitatively (NUMBERS!)

43. Concentrated vs. Dilute Lots of solute, in a small amount of solvent. Small amount of solute in a large amount of solvent. Notice how dark the solutions appears. Notice how light the solution appears. CONCENTRATEDDILUTE

44. Making solutions 1) Pour in a small amount of the solvent, maybe about one-half 2) Then add the pre-massed solute (and mix by swirling to dissolve it) 3) Carefully fill to final volume.

46. Molarity: a unit of concentration Molarity = n (moles of solute) V (liters of solution) Abbreviated with a capital M, such as 6.0 M This is the most widely used concentration unit used in chemistry.

47. - Page 481

48. 1. How many grams of sodium chloride, NaCl, do you need to prepare 250.mL of a 0.5M NaCl solution? Molar mass NaCl= 58.5 g/mol Molarity= nn= mass V molar mass n= Molarity x V = 0.5 mol 0.250L =0.125 mol L Mass= molar mass x n = 58.5 g 0.125 mol = 7.31 g mol

49. 2. What volume of a 1.0M NaCl solution can you prepare if you have 45.0g of NaCl? Molar mass NaCl = 58.5g / mol? n= mass = 45.0 g mol = 0.769 mol molar mass 58.5 g Molarity (M) = n V= n = 0.769 mol L =0.769 L V M 1.0 mol Classwork : p 54 # 19-21

50. Percent solutions can be expressed by a) volume or b) mass Percent by volume: = Volume of solute x 100 Volume of solution indicated %(v/v) V solution = V solute + V solvent m solution = m solute + m solvent

51. Percent by mass: = Mass of solute(g) x 100 Volume of solution (mL) Indicated %(m/v) More commonly used Another way to do mass percentage is as mass/mass: Percent by mass: = Mass of solute(g) x 100 Mass of solution (g) –Indicated %(m/m)

52. 1) 4.8 g of NaCl are dissolved in 82 mL of solution. What is the percent of the solution? % (m/V) = mass solute x100 = 4.8 g x 100 = 5.85% volume solution 82 mL 2) How many grams of salt are there in 52 mL of a 6.3 % solution? Mass solute = %(m/v) x volume solution = 6.3 x 52 = 3.28 g 100 100

53. 3. You mix 25.0 g of salt with 225g of water. What is the %(m/m) concentration of the solution? %(m/m) = mass solute x 100 (mass solute + mass solvent) %(m/m) = 25.0 x 100 = 10% (25.0 + 225.0) Classwork: percent composition handout

54. Dilution Adding water to a solution will reduce the number of moles of solute per unit volume but the overall number of moles remains the same! Think of taking an aspirin with a small glass of water vs. a large glass of water You still have one aspirin in your body, regardless of the amount of water you drank, but a larger amount of water makes it more diluted.

55. Dilution The number of moles of solute in solution doesn’t change if you add more solvent! The # moles before = the # moles after Formula for dilution: M 1 x V 1 = M 2 x V 2 M 1 and V 1 are the starting concentration and volume; M 2 and V 2 are the final concentration and volume. Stock solutions are pre-made solutions to known Molarity.

56. 1. You need to prepare 500. mL of a 0.5M KCl solution. What volume of a 2.0 M KCl solution do you need? M 1 x V 1 = M 2 x V 2 M 1 =2.0M V 1 = ? M 2 = 0.5M V 2 = 500.mL V 1 = M 2 V 2 = 0.5M 500mL = 125 mL M 1 2.0M

57. 2. You add 200 mL of water to 50.0 mL of a 3.0M NaCl solution. What is the new concentration of the solution? M 1 x V 1 = M 2 x V 2 M 1 =3.0M V 1 = 50.0mL M 2 = ? V 2 = 250.mL M 2 = M 1 V 1 = 3.0M 50.0mL = 0.6 M V 2 250mL Classwork: Dilutions handout

58. Colligative Properties of Solutions OBJECTIVES: Identify three colligative properties of solutions. Explain why the vapor pressure, freezing point, and boiling point of a solution differ from those properties of the pure solvent. Solve problems related to the molality and mole fraction of a solution. Describe how freezing point depression and boiling point elevation are related to molality.

59. Colligative Properties -These depend only on the number of dissolved particles -Not on what kind of particle -Three important colligative properties of solutions are: 1) Vapor pressure lowering 2) Boiling point elevation 3) Freezing point lowered

60. Glucose will only have one particle in solution for each one particle it starts with. NaCl will have two particles in solution for each one particle it starts with. CaCl 2 will have three particles in solution for each one particle it starts with. Colligative Properties Some particles in solution will IONIZE (or split), while others may not.

61. Vapor Pressure is LOWERED 1) Surface area is reduced, thus less evaporation, which is a surface property 2) The bonds between molecules keep molecules from escaping. So, in a solution, some of the solvent is busy keeping the solute dissolved. This lowers the vapor pressure Electrolytes form ions when they are dissolved, making more pieces. NaCl  Na + + Cl - (this = 2 pieces) More pieces = a bigger effect

62. Boiling Point is ELEVATED The vapor pressure determines the boiling point. (Boiling is defined as when the vapor pressure of liquid = vapor pressure of the atmosphere). Lower vapor pressure means you need a higher temperature to get it to equal atmospheric pressure Salt water boils above 100ºC The number of dissolved particles determines how much, as well as the solvent itself.

63. Freezing Point is LOWERED Solids form when molecules make an orderly pattern called “crystals” The solute molecules break up the orderly pattern. Makes the freezing point lower. Salt water freezes below 0ºC How much lower depends on the amount of solute dissolved.

64. The addition of a solute would allow a LONGER temperature range, since freezing point is lowered and boiling point is elevated.

65. Molality (abbreviated m) a new unit for concentration m = Moles of solute kilogram of solvent

66. Mole fraction This is another way to express concentration It is the ratio of moles of solute to total number of moles of solute plus solvent moles solute (moles of solute + moles of solvent) The sum of the mole fractions of all the components of a solution equals one. There is no unit for mole fraction. X =

67. Ex.1 Calculate the molality of a solution made by dissolving 45.0g of glucose, C 6 H 12 O 6, in 500.0 g of water. m = Moles of solute kilogram of solvent Moles of solute = 45.0g 1 mol = 0.25 mol 180g m = moles of solute = 0.25 mol = 0.5 m kg of solvent 0.5 kg

68. Ex. 2 What are the mole fractions of glucose and water in a solution made of 7.59g of glucose, C 6 H 12 O 6 dissolved in 125 g of water? Molar mass glucose : 180.0g/mol Molar mass water: 18.0g/mol Mol glucose= 7.59 g mol = 0.0422mol mol water= 125g mol = 6.94 mol 180.0g 18.0g X glucose = moles solute = 0.0422 = 0.00605 (moles solute + moles solvent (0.0422 + 6.94) X wate r = 1 – 0.00605= 0.994

69. CW p 144 # 1-3, 145 # 4-5