chapter 11: properties of solutions by kelly sun and libby takimoto
TRANSCRIPT
CHAPTER 11: PROPERTIES OF SOLUTIONS
By Kelly Sun and Libby Takimoto
11.1
Solution Composition
Ways to Describe Solution Composition
Molarity
Mass Percent
Mole Fraction
Molality
11.2 Energies of Solution Formation
Like Dissolves Like
Making a liquid solution
Enthalpy Changes
1. Expand solute 2. Expand solvent 3. Solute and Solvent interact______________________________________________________________________________________
Heat of Solution △HSoln=△H1+△H2+△H3
Heat of Hydration △HHyd=△H2+△H3
1. Expand solute
2. Expand Solvent
3. Solvent and Solute interact
Making a solution
Factors Effecting Solubility11.3
Structure, Pressure, and Temperature Effects
Structure Effects Polar molecule
Hydrophilic attracted to water Nonpolar molecule
Hydrophobic repels water
Pressure Effects Henry’s Law
= concentration of the dissolved gas = constant characteristic of a solution = partial pressure of the gaseous solute above the solution
Temperature Effects Solids
Solubility occurs more rapidly as the temperature increases Gases
Solubility decreases as the temperature increases
The Vapor Pressures of Solution
11.4
Different Types of Solutions
Nonvolatile in volatile Lowers the vapor pressure of a solute
Volatile in volatile Both contribute to total vapor pressure Increases vapor pressure
Raoult’s Law PSoln=XSolvPº
Solv PTot=XAPºA+XBPº
B
P is Pressure X is mole fraction
Different Types of Solutions cont. Ideal solution Nonelectrolytes vs. Electrolytes Modified Raoult’s Law
PTot=XAPºA+XBPº
B
Used for… Find molar mass and/or moles of solution Characterize solutions
Negative deviations vs. Positive deviations
Boiling-Point Elevation and Freezing-Point Depression11.5
Colligative Properties
A nonvolatile solute elevates the boiling point of the solvent
= change in temperature
= molal boiling-point elevation constant
= molality of solute
The water in solution has a lower vapor pressure than pure water
= change in temperature = molal freezing-point
depression constant = molality of solute
Boiling-Point Elevation Freezing-Point Depression
Osmotic Pressure11.6
Colligative Properties
Osmosis Flow of solvent into the solution through the
semipermeable membrane Osmotic pressure
Minimum pressure that stops the osmosis is equal to the osmotic pressure of the solution
Π = molarity of the solution = gas law constant = Kelvin temperature
Dialysis and Isotonic Solutions
Dialysis Occurs at the walls of most plant and animal cells Impure blood passes through a semi-permeable tube
immersed in a “washing solution” and is cleansed Isotonic solutions
Solutions that have identical osmotic pressures Crenation
When cells are placed in hypertonic solutions, they shrivel
Hemolysis When cells are placed in hypotonic solutions, they
swell
Reverse Osmosis
Reverse osmosis If a solution in contact with pure solvent
across a semipermeable membrane is subjected to an external pressure larger than its osmotic pressure
Solvent flows from the solution to the solvent Desalination
Process of removing salt from salt water
Colligative Properties of Electrolyte Solutions11.7
Van’t Hoff Factor
Expected value for i Ions per formula unit
Observed value for i Lower than expected
Due to ion pairing Modified equations
△T=imK Π=iMRT
Colloids11.8
Colloids
Tyndall effect Scattering of light by particles
Colloid Suspension of tiny particles 1-1000 nm Classified by states and dispersing medium
Electrostatic repulsion Usually neutral, but in electric field, particles
migrate to same electrode and have same charge Same charges repel each other & do not
aggregate
Colloids cont.
Coagulation Destruction of colloid
Heating- increases velocities, ion barriers penetrated to aggregate
Adding electrolyte- neutralizes ion layers
Chapter 11 Equations
Molarity Mass Percent Mole Fraction Molality Raoult’s Law PSoln=XSolvPº
Solv
Boiling-Point Elevation Freezing-Point Depression Osmotic Pressure Van’t Hoff Factor
PRACTICE PROBLEMS
Practice Problem #1
A solution is prepared by mixing 1.00 g ethanol () with 100.0 g water to give a final volume of 101 mL. Calculate the molarity, mass percent, mole fraction, and molality of ethanol in this solution.
Answer: .215M, .990%, .00389, .217m
Practice Problem #2
Calculate the freezing and boiling point of a solution of 100g of ethylene glycol (C2H6O2) in 900g of water.
Answer: Freezing point= -3.33, Boiling point= 100.9
Practice Problem #3
A 0.15-g sample of a purified protein is dissolved in water to give 2.0 mL of solution. The osmotic pressure is found to be 18.6 torr at 25Calculate the protein’s molar mass
Answer: 75,000 g/mol
Practice Problem #4
Calculate the freezing point and boiling point of an anti-freeze solution that is 50.0% by mass of ethalene glycol (HOCH2CH2OH) in water. Ethalene glycol is a nonelectrolyte.
Answer: Boiling Point = 108.2Freezing Point = -29.9
Practice Problem #5
What is the composition of a methanol (CH3OH)-propanol (CH3CH2CH2OH) solution that has a vapor pressure of 174 torr at 40? At 40, the vapor pressure of pure methanol and pure propanol are 303 and 44.6 torr, respectively. Assume the solution is ideal.
Answer: