Lecture 4. Colligative Properties Flashcards
What is the triple point ?
Temperature and pressure at which solid, liquid and gas phases of a substance coexist in equilibrium
What is the critical point ?
The state of a fluid at which the liquid and the gas phases have the same density.
What is vapor pressure ?
The pressure exerted by a vapor in equilibrium with its condensed phases at a given temperature in a closed system.
What is the boiling point ?
The boiling point of a liquid is the temperature at which the vapor pressure of the liquid is equal to the surrounding pressure
What is evaporation ?
The liquid to vapor transition below the boiling temperature of the liquid. Liquids evaporate quicker as temperature rises
What is boiling ?
Occurs at boiling point, when all the molecules in the liquid have enough kinetic energy to vaporise
What happens in evaporation when vapor pressure is less than atmospheric pressure ?
Bubbles cannot form
What happens in boiling when vapor pressure equals atmospheric pressure ?
Bubbles can form and rise
What is a colligative property ?
A property that depends only on the total concentration of solute species (number of solute molecules present) not their identity
Give an example of a colligative property ?
No difference between NaCl and NaBr
What do colligative properties include ?
- Vapor pressure lowering
- Boiling point elevation
- Freezing point depression
- Osmotic pressure
What is the vapor pressure of a solvent in a solution containing a non-volatile solute ?
Always lower than the vapor pressure of pure solvent at the same temperature
What happens when vapor pressure is lowered ?
- The non-volatile solute particles take the place of the solvent particles at the surface, reducing the surface area available to solvent particles
- This causes a decrease in the number of solvent particles that evaporate and reduce the rate of solvent vaporisation
- This lowers the vapor pressure of the solution
What happens to the vapor pressure of the solvent when the concentration of solute is increased ?
Vapor pressure of the solvent is lowered
What does Raoults Law describe ?
The relationship between the vapor pressures of solution components and concentration of these components
What is Raoult’s Law ?
States that the partial pressure exerted by any component of an ideal solution is equal to the vapor pressure of the pure component multiples by its mole fraction in the solution
What effects the difference in a solution of a non-volatile solute that always has a lower vapor pressure than that of the pure solvent ?
The mole fraction of the solvent
What happens to the vapor pressure to an ideal solution dissolving a non- volatile solute where the vapor pressure of the pure component equals zero into a solvent ?
The vapor pressure above the solution is only due to the solvent
What is the vapor pressure of a solution of two volatile solvents ?
The sum of the two pure vapor pressures
What effects boiling point ?
Changes in pressure
What fact does boiling point elevation refer to ?
Compared to the pure solvent, a solution requires a higher temperature to achieve any given vapor pressure, including one equivalent to that of the surrounding atmosphere
When does liquid boil ?
When vapor pressure equals atmospheric pressure
What happens in solution to vapor pressure ?
It is reduced when compared to the pure solvent
What is the relationship between boiling point elevation and the molal concentration of solute species ?
Directly proportional
When does the boiling point of elevation increase ?
When the concentration of the solute increases
How does the addition of more solute effect the boiling point of the solution ?
Large increase in boiling point
What happens in a volatile solvent during freezing point depression ?
Particles in the solid can shift into the liquid phase at the normal freezing point temperature
What happens in a solution with volatile solvents and non-volatile solute ?
Particles in the liquid phase cannot shift into the solid phase at the normal freezing point temperature because solute particles block movement from the liquid into the solid phase
What is a decrease in freezing point called ?
A freezing point depression
What is the relationship between freezing point depression and the molal concentration of solute species ?
Directly proportional
What are some examples of freezing point depression ?
- Sea water
- De-icing or road salting
- Antifreeze
What is osmosis ?
The spontaneous net movement of solvent molecules through a semipermeable membrane into a region of higher solute concentration
What is selective permeation ?
Only molecules or ions of a certain size, shape, polarity, charge etc. are capable of passing through the material
What is osmotic pressure ?
The external pressure that would have to be applied to a pure solvent to prevent it from passing into a given solution
What does osmotic pressure arise from ?
The hydrostatic pressure of the column of solution that the osmosis itself produces
When is equilibrium reached in osmotic pressure ?
When the downwards pressure exerted by the column of solution equals the upwards osmotic pressure
What does the osmotic pressure at equilibrium depend on ?
The concentration of solute
What does applying a pressure greater than the osmotic pressure of the solution result in ?
The reversal of osmosis and pushes the solvent molecules from the solution into the pure solvent
What does osmosis help ?
The biological cells maintain their structure
What is a hypotonic solution ?
Net inflow of solvent
What is an isotonic solution ?
Not net flow
What is an hypertonic solution ?
Net outflow
What is a distillation of a solution ?
A techniques used for separating the components from a liquid mixture by using selective boiling and condensation
What is fractional distillation ?
Used by oil refineries to separate the components of crude oil by heating them to a temperature at which one or more fractions of the mixture will vaporise
What is reverse osmosis used for ?
Purifying water
