Chemistry Video 12 Flashcards
Solubility
Maximum amount of solute that can dissolve in a certain amount of solvent
Determined by strength of solute-solute, solute-solvent and solvent-solvent interactions.
Increases with increasing temperature
Saturated solution
Concentration = solubility
Maximum amount of solute added
Unsaturated solution
Concentration = less than solubility
Supersaturated solution
Concentration = more than solubility
Additional solute is precipitate
Gas solubility
Gaseous solute dissolved in liquid solvent.
Gases with dipoles are more soluble in water (has dipoles) than gases without dipoles. Larger non-dipole-containing gases are more soluble in water (has dipoles) than smaller non-dipole-containing gases
Gaseous solutes are more soluble in liquid solvent that has the same bond type (i.e. can be both dipoles or other type of bond, but must be the same type of bond in both solute and solvent to achieve good solubility.)
Solubility and temperature
Increasing temperature will increase solubility of solids in aqueous solution.
Higher temperatures increase the spontaneity of entropically favourable process. Dissolution is entropically favourable
Most gases become less soluble as temperature increases because the gas particles have more kinetic energy, move faster and make fewer interactions
Solubility and partial pressure
The greater the partial pressure of a gas directly above a liquid solution, the higher the solubility of the gas.
Colligative properties definition
Properties of a solution that do not depend on the identity of the solute, but depend on the concentration of the solute
Molality
moles solute / kilograms solvent
Used instead of molarity (moles/L) because if a situation has changing pressure, then the volume of change and the molarity will not be the same.
Mole fraction
Moles substance / total moles
3 types of colligative properties
When solute is added to solvent to make a solution, there will be:
- vapor pressure lowering
- boiling point elevation
- freezing point depression
compared to having only the solvent without the solute mixed in.
These properties do not depend on identity of solute, but only on concentration of solute
Vapor pressure lowering
A colligative property.
Describes the number of gaseous particles at a given temperature.
Depends on surface area of the liquid. Solute particles in the solvent will block some of the solvent particles from vaporizing, lowering the vapor pressure.
There will be fewer particles in gas phase now that the solute is present in the liquid solvent.
Described by Raoult’s Law: (Partial pressure of a component of a solution) = (Vapor pressure of the pure component) * (mole fraction of the component)
Boiling elevation
A colligative property.
Temperature where vapor pressure is equal to atmospheric pressure. Solute particles interfere with process of boiling and will increase boiling point of solution compared to only have the solvent.
(Change in boiling point) = (van’t Hoff factor) * (molality of the solution) * (Kb, which is the boiling point elevation constant)
van’t Hoff factor = number of individual ions; used when dealing with ionic solute
The new boiling point is the old boiling point summed with the change in boiling point determined from the equation above.
Freezing point depression
A colligative property.
Solute particles interfere with freezing.
(Change in freezing point) = (van’t Hoff factor) * (molality of the solution) * (Kf, which is the freezing point depression constant)
van’t Hoff factor = number of individual ions; used when dealing with ionic solute
The new freezing point is the old freezing point subtract the change in freezing point determined from the equation above.
Osmotic pressure
A colligative property.
It is the pressure that a solution exerts due to osmosis.
Solvent particles can pass through a semi-permeable membrane but solute particles cannot pass through. In a U-tube, the solvent will go to one arm of the U, which causes the right arm to climb up against gravity. The difference between the liquid levels in the left and right side of the U arms is equal to the osmotic pressure.
pi = (van’t Hoff factor) * (molarity of solution) * (gas constant) * (temperature)
where pi = osmotic pressure
van’t Hoff factor = number of individual ions; used when dealing with ionic solute
Higher concentration = greater pressure
Higher temperature = greater pressure
