Solutions

1. Solutions Mechanisms and Phenomena, Separations, and Concentration Problems

2. Solutions How they form, What they do, Separations, and Concentration Problems

3. Standards • 6. Solutions are homogeneous mixtures of two or more substances. As a basis for understanding this concept: • a. Students know the definitions of solute and solvent. • 6. b. Students know how to describe the dissolving process at the molecular level by using the concept of random molecular motion. • 6. c. Students know temperature, pressure, and surface area affect the dissolving process. • 6. d. Students know how to calculate the concentration of a solute in terms of grams per liter, molarity, parts per million, and percent composition. • 6. e.* Students know the relationship between the molality of a solute in a solution and the solution’s depressed freezing point or elevated boiling point. • 6. f.* Students know how molecules in a solution are separated or purified by the methods of chromatography and distillation.

6. Examples of Chemical Change vs. Physical Change Burning Boiling Rusting Freezing Bread Rising Melting Photosynthesis Mixing Salt dissolving in H2O Salt precipitating from H2O

7. Chemical Change Chemical changes occur when the atoms in a substance change their electron configurations. Chemical changes are often noticeable due to the appearance of a new substance or the release or absorption of energy (light, heat, electricity).

8. Reaction Symbols SymbolMeaning (s), (l), (g) Substance is a solid, liquid, or gas (aq) Aqueous, substance is dissolved in H2O “Produces” or “makes” “Produces” through reversible reaction heat orΔ Heat is added to the reactants Pt A catalyst is used to speed up the reaction

9. Definitions • Heterogeneous – a mixture with large particles (clumps of molecules or ions). • Homogeneous – a mixture with very small particles (individual molecules or ions). • Solution – a homogeneous mixture of two or more substances. (ex. salt in water) • Solvent – the main ingredient of a solution. (ex. water) • Solute – the other ingredients dissolved into the solvent. (ex. salt)

10. More Definitions • Solution – a homogeneous mixture of two or more substances. (ex. salt in water) • Solvent – the main ingredient of a solution. (ex. water) • Solute – the other ingredients dissolved into the solvent. (ex. salt) • Colloid – a heterogeneous mixture of two or more substances with medium-sized particles. Usually stable. (ex. whipping cream, mayonnaise, Jell-O) • Suspension – a heterogeneous mixture of two or more substances with larger-sized particles. Usually unstable. (ex. clay in water, smoke in air)

11. Diffusion of Gases

12. Ionic compounds

13. Ionic compounds

14. Ionic compounds

15. Polar molecules – – – + + + + + + H H H O O O H H H

16. Ionic compounds – – – – – – + + + + + + Na Na Na Na Na Na Cl Cl Cl Cl Cl Cl

17. NaCl Dissolved in Water – – – – + + + + + + + + H H H H – Cl O O O O H H H H

18. NaCl Dissolved in Water – – – – + + + + + + + + H H H H + Na O O O O H H H H

19. NaCl Dissolved in Water

20. NaCl Dissolved in Water

21. Sucrose Dissolved in Water

22. Precipitate Precipitate – A solid that comes out of the solution. Iron (II) hydroxide benzoic acid

23. Precipitate • lead (II) nitrate

24. Concentrations • Concentration – how much solute is dissolved within a certain amount of solution. • g solute/L solution • ppm – parts per million (mass) • ppb – parts per billion • Molarity (M) – mol solute/L solution • Molality – mol solute/kg solvent • % composition = mass solute/mass total

25. Concentrations Examples g solute L solution = 3.7 g NaCl 1 L solution ppm – parts per million (mass) = = 25 ppm(mass) 25 g LiF 1,000,000 g solution 3.0 mol MgCl2 1 L solution mol solute L solution Molarity (M) = = = 3.0 M MgCl2 solution

26. Concentrations Examples Molality – mol solute/kg solvent % composition = mass solute/mass total

27. Concentration Example #1 • If 12 moles of KCl are dissolved in a 3 L solution with water, what is the molarity of the KCl solution? 12 mol KCl 3 L solution = 4 M KCl solution

28. Concentration Example #2 • How many moles of sodium chloride (NaCl) are dissolved in 5 L of NaCl solution with a concentration of 3M? 5 L solution 1 3 mol NaCl 1 L solution x = 15 mol NaCl OR 3 molNaCl 1 L solution x molNaCl 5 L solution =

29. Solubility • soluble – something that can dissolve into a solution. • insoluble – something that cannot dissolve into a solution. • saturated – no more solute can dissolve into the solution. • unsaturated – more solute can still dissolve into the solution.

30. Solubility • supersaturated – more than the normal amount of solute is dissolved in the solution. A slight change may force the excess solute to precipitate out of solution.

31. Solubility Graph

32. Solubility Graph

33. Solubility Graph

34. Electrical Conductivity • Distilled water does not conduct electricity • Electrolytes – dissolved salts or acids that allow water to conduct electricity because of positive or negative ions.

35. Diluting Solutions • While the molarity (M) and the volume (V) may change, the number of moles (M × V) will not change. M1 × V1 = M2× V2 before after

36. Diluting Example #1 • 5.0 liters of a 3.0 M NaCl solution is diluted so the volume of the solution is now 30 liters. What is the molarity of the diluted solution? M1 × V1 = M2× V2 (3.0 M) × (5.0 L) = M2× (30 L) 15 = 30 M2 30 30 0.5 M = M2

37. Like Dissolves Like • Polar molecules dissolve polar molecules. • Water, alcohols, vinegar • Nonpolar molecules dissolve nonpolar molecules. • Fats, oils, gasoline • Usefulness of soap in washing off greasy hands comes from soap molecules having both polarandnonpolar ends.

38. Factors that Affect Solubility • Surface Area – Smaller particles have more surface area than larger particles. Surface area allows the solute to dissolve faster.

39. Factors that Affect Solubility • Surface Area – Smaller particles have more surface area than larger particles. Surface area allows the solute to dissolve faster.

40. Factors that Affect Solubility • Stirring – increases solute’s contact with low concentration solvent. The solute dissolves faster. • Temperature – Higher temperatures usually allow more solids to dissolve in liquids but less gases. • Pressure – Higher pressures usually allow more gases to dissolve in liquids.

41. Gas Dissolved in Water

42. Concentration Effects(aka Colligative Properties) • Depressed Freezing Point (anti-freeze, salting the roads and sidewalks in winter) – freezes at a lower temperature because of the solute. • Elevated Boiling Point (anti-boil radiator fluid) – boils at a higher temperature because of the solute.

43. Separations • Decanting – carefully pouring the solution from a container while leaving the precipitate. • Centrifugation – spinning a suspension very fast so the precipitate settles on the bottom. • Filtration – using a filter to trap the precipitate while the solution passes through. • Evaporation – heating and evaporating out the solvent so only the solute remains. • Chromatography – Utilizing different substances’ varying attraction to certain materials so one substance travels faster than the other. • Distillation – Separating 2 liquids heating them both and having them boil out at their different boiling points.

44. Decanting • Decanting – carefully pouring the solution from a container while leaving the precipitate.

45. Centrifugation • Centrifugation – spinning a suspension very fast so the precipitate settles on the bottom.

46. Filtration • Filtration – using a filter to trap the precipitate while the solution passes through.

47. Evaporation • Evaporation – heating and evaporating out the solvent so only the solute remains.

48. Chromatography • Chromatography – Utilizing different substances’ varying attraction to certain materials so one substance travels faster than the other.

49. Distillation • Distillation – Separating 2 liquids heating them both and having them boil out at their different boiling points.

50. Concentration Example #3 • Pure gold nuggets are very rare. Instead most mining companies settle for rocks that contain only small amount of gold. If a 1,000 g rock contains 200 mg of gold, then what is the concentration in parts per million of gold in the rock? 200 mg Au 1,000 g rock = 200 g Au 1,000,000 g rock 0.200 g Au 1,000 g rock 1,000 1,000 = x = 200 ppm Au (mass)