1. Solutions Chapter 13 Properties of Solutions

2. Solutions Solutions are _______________ mixtures of two or more pure substances. In a solution, the _______________ is dispersed uniformly throughout the _______________.

3. Solutions The intermolecular forces between solute and solvent particles must be strong enough to compete with those between solute particles and those between solvent particles.

4. Solutions How Does a Solution Form? As a solution forms, the solvent pulls solute particles apart and surrounds, or _______________, them.

5. Solutions How Does a Solution Form If an ionic salt is soluble in water, it is because the ion- dipole interactions are strong enough to overcome the _______________of the salt crystal.

6. Solutions Energy Changes in Solution Simply put, three processes affect the energetics of the process:  _______________ of solute particles  Separation of _______________ particles  New _______________ between solute and solvent

7. Solutions Energy Changes in Solution The enthalpy change of the overall process depends on  H for each of these steps.

8. Solutions Why Do Endothermic Processes Occur? Things do not tend to occur _______________ (i.e., without outside intervention) unless the energy of the system is _______________.

9. Solutions Why Do Endothermic Processes Occur? Yet we know that in some processes, like the dissolution of NH 4 NO 3 in water, heat is _______________, not released.

10. Solutions Enthalpy Is Only Part of the Picture The reason is that increasing the _______________or randomness (known as _______________) of a system tends to lower the _______________ of the system.

11. Solutions Enthalpy Is Only Part of the Picture So even though enthalpy may increase, the overall energy of the system can still decrease if the system becomes more _______________.

12. Solutions Types of Solutions _______________  Solvent holds as much solute as is possible at that temperature.  Dissolved _______________ is in dynamic equilibrium with solid solute particles.

13. Solutions Types of Solutions _______________  Less than the maximum amount of solute for that temperature is dissolved in the _______________.

14. Solutions Types of Solutions _______________  Solvent holds more solute than is normally possible at that temperature.  These solutions are _______________; crystallization can usually be stimulated by adding a “seed crystal” or scratching the side of the flask.

15. Solutions Factors Affecting Solubility Chemists use the axiom “like dissolves like”:  _______________ substances tend to dissolve in polar solvents.  _______________substa nces tend to dissolve in nonpolar solvents.

16. Solutions Factors Affecting Solubility The more similar the _______________ attractions, the more likely one substance is to be soluble in another.

17. Solutions Factors Affecting Solubility Glucose (which has hydrogen bonding) is very soluble in water, while cyclohexane (which only has dispersion forces) is not.

18. Solutions Factors Affecting Solubility Vitamin A is soluble in nonpolar compounds (like fats). Vitamin C is soluble in water.

19. Solutions Gases in Solution In general, the solubility of gases in water _______________ with _______________ mass. Larger molecules have stronger dispersion forces.

20. Solutions Gases in Solution The solubility of liquids and solids does not change appreciably with _______________. The solubility of a gas in a liquid is directly proportional to its _______________.

21. Solutions Temperature Generally, the solubility of solid solutes in liquid solvents _______________ with increasing temperature.

22. Solutions Temperature The opposite is true of gases:  Carbonated soft drinks are more “bubbly” if stored in the refrigerator.  Warm lakes have less O 2 dissolved in them than cool lakes.

23. Solutions Ways of Expressing Concentrations of Solutions

24. Solutions Mass Percentage Mass % of A = mass of A in solution total mass of solution  100

25. Solutions moles of A total moles in solution X A = Mole Fraction (X) In some applications, one needs the mole fraction of _______________, not solute—make sure you find the quantity you need!

26. Solutions mol of solute L of solution M = Molarity (M) You will recall this concentration measure from Chapter 4. Because volume is temperature dependent, molarity can change with temperature.

27. Solutions mol of solute kg of solvent m = Molality (m) Because both moles and mass do not change with _______________, molality (unlike molarity) is _______________ temperature dependent.

28. Solutions Changing Molarity to Molality If we know the density of the solution, we can calculate the molality from the molarity, and vice versa.

29. Solutions Colligative Properties Changes in _______________ properties depend only on the number of _______________ particles present, not on the _______________ of the solute particles. Among colligative properties are  Vapor pressure lowering  Boiling point elevation  Melting point depression

30. Solutions Vapor Pressure Because of solute- solvent intermolecular attraction, higher concentrations of _______________ solutes make it harder for solvent to escape to the vapor phase.

31. Solutions Vapor Pressure Therefore, the vapor pressure of a solution is _______________tha n that of the pure solvent.

32. Solutions Boiling Point Elevation and Freezing Point Depression _______________ solute-solvent interactions also cause solutions to have _______________ boiling points and _______________ freezing points than the pure solvent.

33. Solutions Boiling Point Elevation The change in boiling point is proportional to the molality of the solution:  T b = K b  m where K b is the molal boiling point elevation constant, a property of the solvent.  T b is added to the normal boiling point of the solvent.

34. Solutions Freezing Point Depression The change in freezing point can be found similarly:  T f = K f  m Here K f is the molal freezing point depression constant of the solvent.  T f is subtracted from the normal freezing point of the solvent.

35. Solutions Boiling Point Elevation and Freezing Point Depression Note that in both equations,  T does not depend on what the solute is, but only on how many particles are dissolved.  T b = K b  m  T f = K f  m

36. Solutions Colligative Properties of Electrolytes Since these properties depend on the number of particles dissolved, solutions of _______________ (which dissociate in solution) should show greater changes than those of nonelectrolytes.

37. Solutions Colligative Properties of Electrolytes However, a 1 M solution of NaCl does not show twice the change in freezing point that a 1 M solution of methanol does.

38. Solutions van’t Hoff Factor One mole of NaCl in water does not really give rise to two moles of ions.

39. Solutions van’t Hoff Factor Some Na + and Cl − reassociate for a short time, so the true concentration of particles is somewhat less than two times the concentration of NaCl.

40. Solutions The van’t Hoff Factor Reassociation is more likely at higher _______________. Therefore, the number of particles present is _______________ dependent.

41. Solutions The van’t Hoff Factor We modify the previous equations by multiplying by the van’t Hoff factor, i  T f = K f  m  i

42. Solutions Colloids: Suspensions of _______________ larger than individual ions or molecules, but too _______________to be settled out by gravity.