1. Solutions and Mixtures

2. Solutions Solutions are stable, homogeneous mixtures
Particles are evenly distributed through the mixture
Will not spontaneously separate
There are two parts: solute and solvent

3. Parts of a Solution Solute: the substance being dissolved
Solvent: the substance doing the dissolving (think water: universal solvent)

4. Classes of Solutions
Classes are based on the final state of matter of the sol’n
Three classes:
Gaseous sol’ns: mixtures of two gases
Liquid sol’ns: gas, liquid, or solid is dissolved in a liquid
Solid soln’s: solid and a liquid or two solids are melted, mixed, or cooled
Alloys: solid solutions containing metals

5. Solution of a gas (hydrogen) in a solid (palladium)

6. Examples of solid solutions

7. Ways to Describe Solutions
There are three ways to describe concentrations:
Molarity
Molality
Mole fraction

8. Molarity
Molarity (M): # of moles of solute dissolved in each liter of sol’n
M = moles of solute
liters of sol’n
Four different labels: molarity, molar, M, or mol/L
Dependent on temp
Volumetric flasks are the best containers for making a sol’n of a precise molarity

9. What is the molarity of a sol’n prepared by dissolving 16
What is the molarity of a sol’n prepared by dissolving 16.0 g of barium chloride in enough water to give 450 mL of sol’n?

10. How many grams of potassium chloride are needed to prepare 0
How many grams of potassium chloride are needed to prepare 0.750L of a 1.50M sol’n of potassium chloride?

11. Molality
Molality (m): # of moles dissolved in each kilogram of solvent
m = moles of solute
kg of solvent
Independent of temp

12. Calculate the molality of a sol’n prepared by dissolving 20
Calculate the molality of a sol’n prepared by dissolving 20.4 g of sodium chloride in 192g of water.

13. What is the molality of a solid sol’n containing 0
What is the molality of a solid sol’n containing 0.125g of chromium and 81.3g of iron?

14. Mole Fraction
Mole fraction (X): # of moles of one component divided by the total # of moles in the sol’n
X = moles of component
total moles of sol’n
Used to compare solute and solvent

15. What are the mole fractions of ethyl alcohol (C2H5OH) and water in a sol’n prepared by adding 50.0g of ethyl alcohol to 50.0g of water?

16. A gas mixture contains the following gases with the mole fractions indicated: CH4 (0.510), C2H6 (0.431), C3H8 (0.011), and C4H10 (0.013). The mixture also contains the gas acetylene (C2H2). What is the mole fraction of acetylene?

17. Solution Terms Most sol’ns are combinations of liquids and solids
Miscible: liquids or gases that will dissolve in each other
Immiscible: liquids or gases that will not dissolve in each other
Soluble: able to be dissolved in a particular solvent
Insoluble: not able to be dissolved in a particular solvent

18. Concentrations
Concentrated solution: a large amount of solute is dissolved in the solvent
Dilute solution: a small amount of solute is dissolved in the solvent

19. Saturation
Saturated sol’n: a sol’n that has dissolved all the solute it can hold at a given temp
NOT the same as concentrated
Sol’n can be saturated but not concentrated and vise versa

20. Saturation (cont)
Unsaturated sol’n: any sol’n that can dissolve more solute at a given temp
Supersaturated sol’n: sol’n that contains more solute than a saturated one has at that temp
It is unstable
Crystallization from Supersaturated Solutions of Sodium Acetate

22. Determining Saturation
Add a solute crystal to a sol’n
If dissolves: unsaturated
If does not dissolve: saturated
If excess solute comes out: supersaturated

23. The Formation of Sol’ns
The process of dissolving takes place at the surface of the solid solute
Water molecules orient themselves on the surface of the crystal so that they can separate the pieces and pull them into sol’n
Once separated, the pieces are surrounded by water molecules

25. Formation of Soln (cont)
Solvation: process of surrounding solute particles with solvent particles
Hydration: solvation involving water
Formation of a sol’n involves:
Breaking the attractions among solute particles
Breaking the attractions among solvent particles
Formation of attractions between solute and solvent particles

26. Heat of Solution
Defined as overall energy change that occurs during solution formation
Energy is required for formation of sol’ns
Breaking attractions – endothermic
Forming attractions – exothermic
Overall process (net change) depends on the balance between breaking and forming attractions
If breaking requires more energy – endothermic
If forming releases more energy - exothermic

27. Solubility
Defined as the maximum amount of a solute that will dissolve in a given amount of solvent at a specific temp
Determined experimentally
Usually expressed in grams of solute per 100 grams of solvent at a specific temp and pressure

28. Solubility Based on the idea of attractions between particles
Overall polarity determines solubility:
“Like dissolves like”
Polar dissolves polar
Nonpolar dissolves nonpolar

30. Picture of a soap micelle.

31. Solvation
The extent to which one substance dissolves in another depends on:
State of solute and solvent
Temp and pressure
Solubilities change with temp (the key to preparing a supersaturated sol’n)
Solubility of solids and liquids increases
Solubility of gases in liquids decreases

32. Solubilities of Substances in Water

33. Solubilities of Gases in Water

34. Henry’s Law
Solubilities of solids and liquids are not appreciably affected by pressure, but solubility of a gas in a liquid is strongly influenced by pressure
Henry’s Law: the amount of gas dissolved in a solvent is proportional to the partial pressure of that gas over the solvent

35. The solubility of a gas depends upon its partial pressure above the solution.

36. Factors that Affect Rate of Solvation
Must increase the collisions between solute and solvent particles to increase rate at which solute dissolves.
Three ways:
Agitate mixture (stir, shake)
Increase surface area (breaking solute into small pieces)
Increase temp of solvent

37. Increasing surface area does the same thing
Because dissolving occurs at the surface, stirring/shaking allows more solvent to come in contact with solute
Increasing surface area does the same thing
As temp increases, solvent particles move faster, which causes more particles to come in contact with the solute.
Particles of solvent have more energy to remove particles from the solid solute

38. Aqueous Solutions Ionic compounds dissociate in water
Dissociate: a process using energy to separate a compound into ions in water
Molecular compounds may also dissociate in water
Some aqueous solutions conduct electricity

39. Aqueous Soln’s
Conductance: the measurement of a sol’n’s ability to conduct electrical energy
Electrolyte: any substance that will conduct an electric current (by means of movement of ions), when dissolved in sol’n
Nonelectrolyte: any substance that will not conduct an electric current when dissolved in water

40. Colligative Properties
A physical property that is dependent on the # of particles present rather than on the size, mass, or characteristics of those particles
Four main properties:
Vapor pressure reduction
Boiling point elevation
Freezing point depression
Osmotic pressure

41. Vapor Pressure Reduction
Vapor pressure of a solvent containing a nonvolatile solute is lower than the vapor pressure of the pure solvent
Volatile means tending to evaporate readily
Vapor pressure reduction is proportional to concentration

42. When a solute is added to the solvent, some of the solute molecules occupy the space near the surface of the liquid, as shown in the figure to the left. When a solute is dissolved in a solvent, the number of solvent molecules near the surface decreases, and the vapor pressure of the solvent decreases.

43. Boiling Point Elevation
Because vapor pressure is lower, a higher temp will be needed to make the sol’n boil
The amount by which the boiling point is raised is the boiling point elevation (ΔTb)
It is directly proportional to the sol’n’s molarity

44. A close-up plot of vapor pressure versus temperature for pure water (red curve) and for a 1.0 M NaCl solution (green curve). Pure water boils at 100.0°C, but the solution does not boil until 101.0°C.

45. Freezing Point Depression
The presence of solute molecules will lower the freezing point of a substance
The more solute particles in sol’n, the greater the lowering of the freezing pt
Freezing pt depression: the ability of a dissolved solute to lower the freezing point of its sol’n
Why does salt melt ice?

46. Osmotic Pressure
When a semipermeable membrane is placed between 2 sol’ns so that only solvent particles can move through it, a net flow of solvent molecules will occur from the less concentrated sol’n to the more concentrated sol’n (osmosis)
Osmotic pressure: the pressure required to prevent osmosis
If 2 different sol’ns have identical osmotic pressure, no osmosis will occur (isotonic)

47. A solution inside the bulb is separated from pure solvent in the container by a semipermeable membrane. Net passage of solvent from the container through the membrane occurs, and the liquid in the tube rises until an equilibrium is reached. At equilibrium, the osmotic pressure exerted by the column of liquid in the tube is sufficient to prevent further net passage of solvent.

48. Heterogeneous Mixtures
Suspension: mixture that appears to be uniform while being stirred, but separates into different phases when agitation ceases
Colloid: heterogeneous mixture that contains intermediate size particles evenly distributed through a dispersion medium

50. Heterogeneous Mixtures
Brownian Motion: jerky, erratic movement of dispersed particles
Prevent colloids from settling out
What is Brownian Motion?
Tyndall effect: scattering of light by dispersed particles

51. The light beam is not visible as it passes through a true solution (right), but it is readily visible as it passes through colloidal silver in water.

52. Tyndall effect in clouds.