Chapter 11.4 - Colligative Properties

Colligative Properties

Colligative properties depend primarily on what?

The concentration of solute particles

What are the 4 colligative properties covered in this chapter?

Vapor pressure lowering, boiling point elevation, freezing point depression, osmotic pressure

Colligative properties describe the possible effects/modifications when…

A solute is added to a solvent

Colligative properties depend only on the _______ of solute particles, not the kind; however, in these calculations, it may be necessary to determine the number of ___ present in the solution as well.

number, ions

What are the 4 methods for describing solution composition

Molarity, mass percent, mole fraction, molality

Mass percent equation

Mass % = (Mass of Solute/Mass of Solution) x 100%

Mole fraction equation

XA = [ (mole A)/(mol A + mol B + mol C)]

Mole fraction is used when there is a what?

A mixture of A, B, and C substances

Molality equation

m = (mole of solute/kg of solvent)

To convert from moles to mass, what do you need?

The molar mass

To convert a term from mass to volume, what do you need?

The solution density

When a solute is added to a solvent, the vapor pressure ________, the melting point and freezing point _______, the boiling point ______ and osmosis becomes _______.

decreases, decrease, increases, possible

When a solute is added to a solvent, the ______ _______ , _______ _______, and ______ ______decrease, the ______ _____ increases, and _______ becomes possible.

vapor pressure, melting point, freezing point, boiling point, osmosis

Why do colligative properties occur?

The presence of a nonvolatile solute lowers the vapor pressure of a solution by impeding the evaporation of solvent molecules

What law describes vapor pressure lowering?

Raoult’s Law

Raoult’s Law

The vapor pressure of an ideal solution is directly proportional to the vapor pressure of each component and their respective mole fractions

What equations derives from Raoult’s Law?

[P_solution = X_solvent x P^o_solvent] and [P_solvent = (mole fraction of solvent) x (VP of pure solvent)]

Boiling point elevation equation

deltaT = K_bmolality_solute

Freezing point elevation equation

deltaT = K_fmolality_solute

What is the Van’t Hoff factor; What is its symbol?

The number of particles produced per formula unit; i

What types of solutes does the Van’t Hoff factor mostly apply to?

Ionic solutes

Osmosis

The flow of solvent through a semi-permeable membrane from solution of low concentration to solution of high concentration

Osmotic pressure

The amount of pressure needed to keep osmotic flow from taking place

What is the equation for osmotic pressure?

Osmotic pressure = MRT

Why does osmosis occur; when does osmosis stop?

The solvent on one end has a driving force that moves it through the semi permeable membrane to increase the number of solvent molecules on the other side; when the osmotic pressure produces an equal rate of transfer in both directions

Reverse osmosis occur when what happens? What does this cause?

When a greater pressure than the osmotic pressure is applied; causes solvent molecules from the solution to push into the pure solvent

Types of Osmotic Solutions

Isosmotic, Hyperosmotic, Hypoosmotic

Isosmotic

When osmotic pressure inside the cell equals the pressure outside of the cell

Hyperosmotic

When there is a higher solute concentration inside of the cell, causing water to move out

Hypoosmotic

When there is a lower solute concentration inside of the cell, causing water to move in

Colloidal Suspension

A heterogenous mixture in which one substance is dispersed through another

What is the difference between colloids and regular suspensions?

Particle size - colloids contain smaller particles

What are the two main properties of colloids?

Brownian motion and the Tyndall Effect

Brownian Motion

Particles bounce around with no real purpose

Tyndall Effect

The scattering of light as it passes through a suspension

Colloids scatter ___ -wavelength light (blue) more effectively than ____- wavelength light (red)

short, long