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Flashcards in Colligative Properties Deck (28):
1

True Solution

-One-phase, homoogeneous molecular dispersion
-No phase separation or boundary

2

Binary Solution

-Solution with 1 solute and 1 solvent

3

Solvent

First Substance
-For liquids - solvent is [higher]

4

Solute

Second Substance

5

Component/Constituents

-No distinction between solute and solvent

6

Nonelectrolytes

-When dissolved they do NOT form ions
-Will NOT conduct electrical currency
-EX: sucrose, glycerin, urea

7

Electrolytes

-Substances that dissociate into ions when dissolved
-Strong = complete dissociation
-Weak = partial dissociation

8

Additive Property

-Contribution of each atom of the molecule add up
-EX: MW

9

Constitutive Property

-Depending on arrangement of atoms in molecule
-EX: electrical properties, light refraction, solubility

10

Colligative Property

-Number of "particles" in solution

11

Examples of Colligative Properties

-Vapor pressure lowering
-Freezing point depression
-Boiling point elevation
-Osmotic pressure changes

12

Do electrolytes or nonelectrolytes contribute more to colligative properties?

Electrolytes
-Ionization of electrolytes produces more particles

13

Ideal Solutions

-No changes in the properties of the two components when mixed together
-No heat given off or absorbed
-No shrinkage or expansion of volume
-All constitutive properties are weighted averages of each component
-Molecules of solute interact with solvent the same way

**More likely to occur when mixing "like" substances**

14

Real/Non-Ideal Solutions

-Solute molecules interact to a greater or lesser extent with solvent molecules than other solute molecules
-Dependent on interactions between solute and solvent as to if the solution is ideal/real
-Recall vapor pressure of liquids is a reflection of intermolecular bonding
-Greater bonding in liquid state = lower vapor pressure

15

Raoult's Law

-Vapor pressure of a substance in solution os equal to vapor pressure of PURE compound multiplied by its mole fraction

Pa = Pa0 * Xa
Pb = Pb0 * Xb
Pt = Pa + Pb

16

Negative Deviations

-Indicated attractive forces between A and B
-These are GREATER than those between A/A and B/B

17

Positive Deviations

-Indicates attractive fores between A/A and B/B
-These are GREATER than those between A and B

18

Simple Binary Solutions

-Nonelectrolytes
-If the solute is nonvolatile, then the partial pressure of solvent IS the vapor pressure
-Delta P = PaO * 0.018 * m
-m = molality, PaO is vapor pressure of pure SOLVENT

19

Actual Vapor Pressure =

-Difference of the vapor pressure of the pure solvent from delta P (vapor pressure lowering)

20

Relative Vapor Pressure Lowering

-Often referenced as a percentage
-Since compared to "whole" vapor pressure of the pure solvent

21

Boiling Point

-Temperature when the vapor pressure of a solution equals the external pressure
-Nonvolative solute in a solvent will have a higher boiling point than pure solvent (lowered vapor pressure)
-Therefore referred to as boiling point elevation

22

Boiling Point Elevation

-Delta Tb = kb * m
-Kb = molal elevation constant (ebullioscopic constant), 0.51 for aqueous solutions
-m = molality
-Add to original boiling point for actual boiling point of solution
**Dependent on [solute]

23

Freezing Point Depression

-Delta Tf = kf * m
-m = molality
-Kf = cryoscopic constant, 1.86 for water
-Actual freezing point is original minus the freezing point depression

24

Osmotic Pressure

-Osmosis - process of solvent diffusion across a semi-permeable membrane (OP driven)
-No osmosis if OP is the same on either side
-Solvent molecules move towards area of greater osmotic pressure
-Equalizes as solvent dilutes the side with greater pressure by decreasing the solute's concentration

25

[Solute] + Colligative Properties

-Decreases vapor pressure
-Decreases freezing point
-Increases boiling point
-Increases osmotic pressure

26

van't Hoff Equation

-Used to calculate osmotic pressure
-(pi) = m*R*T
-m = molality
-R = gas constnat
-T = temperature in Kelvins

27

Nonelectrolyte Points

-If the two solutions have the same vapor pressure,t hen they have the same osmotic pressure, boiling point, and freezing point too
-All equations to measure pressures and changes in temperatures use molality

28

Solute MW in Binary Solutions

m = (1000 * w2)/(w1 * MW2)
w1 = weight of solvent
w2 = weight of solute
MW2 = molecular weight of solute