chapter 11: properties of solutions by kelly sun and libby takimoto

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: