1. William L Masterton Cecile N. Hurley http://academic.cengage.com/chemistry/masterton Edward J. Neth University of Connecticut Chapter 10 Solutions

2. Outline 1. Concentration units 2. Principles of solubility 3. Colligative properties of nonelectrolytes 4. Colligative properties of electrolytes

3. Review We have looked briefly at the concept of concentration in terms of the solubility Solubility was given in Chapter 1 as the mass of a solute that will dissolve in 100 g of a solvent Other quantities than mass can be used to express concentrations

4. Solutions in Everyday Life Morning coffee Solutions of solids (sugar, coffee) in liquid (water) Gasoline Solution of liquid hydrocarbons Soda Solution of sugar, water and carbon dioxide Air Solution of oxygen and nitrogen

5. 10.1 Concentration Units General Vocabulary: Solution – homogeneous mixture of solute and solvent Solute – the substance being dissolved Solvent – the substance doing the dissolving Electrolyte – a substance the conducts electricity when in solution

6. 10.1 Concentration Units Molarity – (M) moles of solute per liter of solution Molarity = moles of solute/liters of solution Example: What is the molarity of a solution made by dissolving 12.5g of oxalic acid (H 2 C 2 O 4 ) in 456mL of solution?

7. Figure 10.1

8. Dilution of Solutions M 1 V 1 = M 2 V 2

9. Example 10.1

10. Mole Fraction The mole fraction of A is the number of moles of A divided by the total number of moles The mole fractions of all components must add to 1; just like a percent without the x 100

11. Example 10.2

12. Mass Percent, Parts Per Million, and Parts Per Billion Percent by mass = (mass solute/mass solution) * 100 Parts per million(ppm) = (mass solute/mass solution) * 10 6 Parts per billion(ppb) = (mass solute/mass solution)*10 9

13. Molality the number of moles of solute per kilogram of solvent Molality (m) = moles of solute/kilograms of solvent

14. Example 10.3

15. Conversions Between Concentration Units Start with a fixed amount of solution or solvent (see table on page 262) When the original concentration is Choose Mass percent100 g solution Molarity (M)1.00 L solution Molality (m)1.00 kg solvent Mole fraction (X)1.00 mol solution

16. Example 10.4

17. 10.2 Principles of Solubility Factors that determine the extent to which a solute dissolves in a particular solvent: 1. The nature of solvent and solute particles and the interaction between them 2. The temperature at which the solution forms 3. The pressure, in cases of gaseous solutes

18. Solute-Solvent Interactions “Like dissolves like” = see table in notes Polar solutes dissolve in polar solvents Nonpolar solutes dissolve in nonpolar solvents Nonpolar substances have poor affinity for water Petroleum Hydrocarbons (pentane, C 5 H 12 ) Polar substances dissolve easily in water Alcohols, CH 3 OH Solubility of alcohols decreases as the molar mass of the alcohol increases

19. Solubility and Intermolecular Forces

20. Table 10.1

21. Effect of Temperature on Solubility An increase in temperature always shifts the position of an equilibrium to favor an endothermic process heat of solution > 0 heat of solution < 0

22. Figure 10.4 (Solubility Curves – pg 12)

23. Effect of pressure on Solubility Pressure has a major effect on the solubility of a gas in a liquid, but little effect on other systems Henry’s Law - At low to moderate pressure, the concentration of a gas increases with the pressure C g = kP g, where P g is the partial pressure of the gas over the solution C g is the concentration of the gas k is a constant (the Henry’s Law constant)

24. Solubility Effects of Pressure

25. Example 10.5

26. 10.3 Colligative Properties of Nonelectrolytes The properties of a solution may differ considerably from those of the pure solvent Some of these properties depend on the concentration of dissolved particles and not on their nature

27. Vapor Pressure Lowering True colligative property: independent of the nature of the solute but dependent on the concentration The vapor pressure of a solvent over a solution is always lower than the vapor pressure of a pure solvent

28. Boiling and Freezing Point Boiling point elevation and freezing point lowering are both colligative properties K f is the freezing point lowering constant K b is the boiling point elevation constant

29. FPL and BPE Constants for Water For water,

30. Example 10.7

31. Molal Constants

32. Osmotic Pressure The osmotic pressure (symbol π) is the pressure required to prevent osmosis from occurring

33. Figure 10.10

34. Determination of Molar Masses from Colligative Properties MM = grams/moles

35. Example 10.9

36. 10.4 Colligative Properties of Electrolytes When an electrolyte dissolves it breaks apart into ions. NaCl (s)  Na +1 (aq) + Cl -1 (aq) So for every NaCl formula unit 2 aqueous ions are formed The formula is adjusted to reflect the number of ions: ∆T = k m ii = the number of ions formed

37. Example 10.10

38. Solution Stoichiometry Example

39. Solution Stoichiometry Example