What are some special properties of solutions?

1. What are some special properties of solutions? Chemistry Unit 11

2. Main Ideas • Mixtures can be either heterogeneous or homogeneous • Concentration can be expressed in terms of percent or in terms of moles • Factors such as temperature, pressure, and polarity affect the formation of solutions • Colligative properties depend on the number of solute particles in a solution

3. Types of Mixtures 11.1

4. Objectives • Compare the properties of suspensions, colloids, and solutions • Identify types of colloids and types of solutions. • Describe the electrostatic forces in colloids

5. Types of Mixtures Heterogeneous Mixtures are a combination of two or more pure substances in which each pure substance retains its individual properties. There are two main types of heterogeneous mixtures:

6. Types of Mixtures • Suspensions – A suspension is a mixture containing particles that settle out if left undisturbed but, when stirred, the substance will flow like a liquid. • These substances are called thixotropic. These particles can be filtered out. Example : muddy water

7. Types of Solutions • Colloids – A colloid is made of smaller sizes of suspension particles and these particles do not settle out. Particles cannot be filtered out. The most abundant substance in a mixture is the dispersion medium. Example: Milk • Colloids are categorized according to the phases of their particles.

8. Types of Colloids

9. Colloids • The dispersed particles in a colloid are prevented from settling out because they often have polar or charged atomic groups on their surfaces. This results in the formation of electrostatic layers around the particles. • The layers electrostatically repel each other when the dispersed particles collide, thus, the particles remain in the colloid.

10. Colloids • If you interfere with the electrostatic layering, colloid particles will settle out of the mixture. Heating also destroys a colloid because it gives colliding particles enough kinetic energy to overcome the electrostatic forces and settle out.

11. Brownian Motion • Brownian motion is the jerky, random movements of particles in a liquid colloid, from the results of particle collisions.

12. Tyndall Effect Concentrated colloids are often cloudy or opaque. Dilute colloids sometimes appear as clear as solutions. Dilute colloids appear to be homogeneous solutions because their dispersed particles are so small. • The Tyndall effect is when dispersed colloid particles scatter light. • Examples: sunlight through smoke filled air or fog

13. Homogeneous Mixtures A homogeneous mixture is a solution of two or more substances that blend easily and constant composition throughout. There are different types of homogeneous solutions: • A solution might exist as a gas, a liquid, or a solid, depending on the state of its solvent. Water is the most common liquid solvent. • Examples: salt water and steel

14. Types of Solutions

15. Forming Solutions Some combinations of substances readily form solutions, and others do not. • A substance that dissolves in a solvent is said to be soluble in that solvent. • Example: Sugar in water • Two liquids that are soluble in each other are called miscible.

16. Forming Solutions • A substance that does not dissolve in a solvent is said to be insoluble. • Two liquids that cannot be mixed together but separate shortly after are said to be immiscible

17. Questions Miscible substances are: A.two liquids that are not soluble in each other B.solids that dissolve in liquids C.solids that do not dissolve in liquids D.two liquids that are soluble in each other

18. Questions The jerky, random movement of particles in a liquid colloid is known as ____. A.Brownian motion B.Tyndall effect C.Charles’s Law D.kinetic energy

19. Homework • CALM 11.1 • p 479 #2, 4, 6,7

20. Solution Concentration 11.2

21. Objectives • Describe concentration using different units • Determine the concentrations of solutions • Calculate the molarity of a solution.

22. Expressing Concentration Concentration can be expressed in terms of percent or in terms of moles. • The concentration of a solution is a measure of how much solute is dissolved in a specific amount of solvent or solution.

23. Expressing Concentration

24. Practice Problem #1 In order to maintain a sodium chloride (NaCl) concentration similar to ocean water, an aquarium must contain 3.6g NaCl per 100g of water. What is the percent by mass of NaCl in the solution? Answer: 3.5%

25. Molarity • Molarityis the number of moles of solute dissolved per liter of solution. • Dilution equation: M1V1 = M2V2

26. Practice Problem #2 A 100.5 ml intravenous (IV) solution contains 5.10 g of glucose (C6H12O6). What is the molarity of this solution? Ans: 0.282M

27. Practice Problem #3 If you needed to make a 1.0 M solution of CaCl2, how many grams would you need to make 500 ml of it? 5.5g

28. Practice Problem#4: Dilution What volume of 2.00 M calcium chloride stock solution would you use to make 0.50 L of 0.300 M calcium chloride solution? 75 ml or .075L

29. Molality • Molalityis the ratio of moles of solute dissolved in 1 kg of solvent.

30. Practice Problem #5 In the lab, a student adds 4.5g of sodium chloride (NaCl) to 100.0g of water. Calculate the molality of the solution. 0.77 mol/kg

31. where XAand XB represent mole fractions of each substance Mole Fraction • Mole fractionis the ratio of the number of moles of solute in solution to the total number of moles of solute and solvent.

32. Practice Problem #6 100 g of a hydrochloric acid solution contains 36 g of HCl and 64 g of H2O. What are the mole fractions of HCl and water? .22 HCl .78 H2O

33. Question Which is NOT a quantitative measure of concentration? A.molarity B.molality C.percent by mass D.dilute

34. Question The number of moles of solute divided by liters of solvution is called ____. A.molarity B.molality C.percent by volume D.percent by mass

35. Homework • CALM 11.2 • p481-483 #9,10, 16-18 • p485-487 # 20-22, 24, 25, 27, 29

36. Factors Affecting Solvation 11.3

37. Objectives • Describe how intermolecular forces affect solvation. • Define solubility. • Understand what factors affect solubility.

38. Solvation • The process of surrounding solute particles with solvent particles to form a solution is called solvation. • Solvation in water is called hydration. • “like dissolves like”

39. Solvation

40. Factors that Affect Solvation • Agitation – shaken or stirred – agitation of the mixture allows for more contact between solute and solvent. • Surface area – breaking the solute into small pieces helps solvation. A greater surface area allows more collisions to occur.

41. Factors that Affect Solvation • Temperature – As temperature increases, the rate of solvation also increases. Additionally, hotter solvents generally can dissolve more solid solute.

42. Solubility Solubility is the ability of a solvent to dissolve a solute. • In an aqueous solution, a precipitate forms when a mixture produces an insoluble product.

43. Solubility Guidelines • All common salts of the group 1 elements and ammonium ions are soluble. • All common acetates and nitrates are soluble. • All binary compounds of group 17 elements (other than F) with metals are soluble except hoes of silver, mercury (I), and lead.

44. Solubility Guidelines • All sulfates are soluble except those of barium, strontium, lead, calcium, silver, and mercury (I). • Except for those in Rule 1, carbonates, hydroxides, oxides, sulfides, and phosphates are insoluble.

45. Practice Problem #7 Which of the following substances would be a precipitate in an aqueous solution? Why? • NaCl • CaCO3 • Fe(NO3) • KOH

46. Solubility Unsaturated solutions – An unsaturated solution is one that contains less dissolved solute than the solvent can handle at a certain temperature and pressure. • In other words, more solute can be dissolved in an unsaturated solution.

47. Solubility Saturated solution – The maximum amount of solute has been dissolved in the solvent. The amount of crystallization is at equilibrium with the amount of solvation. • In other words: The solution cannot dissolve anymore solute.

48. Solubilty A supersaturated solution contains more dissolved solute than a saturated solution at the same temperature and are considered unstable. • To make a supersaturated solution, a saturated solution is formed at a high temperature and then cooled slowly. • The slow cooling allows the excess solute to remain dissolved in solution at the lower temperature.

49. Solubility of Gases • Gases, in general, are less soluble at higher temperatures than at lower temperatures. At higher temperatures, the gases have a higher kinetic energy that allows them to escape from a solution.

50. Henry’s Law Pressure affects the solubility of gaseous solutes in solutions. The solubility of a gas in any solvent increases as its external pressure increases. • Carbonated beverages rely on the container to provide enough pressure to keep gas dissolved in the solution.