Lecture 3 Flashcards
In general, how does temperature affect solubility of SOLIDS in water?
Solubility increases as temperature increases
How does temperature affect solubility of GASES in water?
Solubility decreases as temperature increases
–> ex: CO2 is more soluble at the bottom of a lake
Story: Because of earthquake, the cold water (containing dissolved CO2) in the bottom of the lake was pushed up. As the temperature of the water increased, the solubility of CO2 decreased and was released into the air.
Which has a higher vapour pressure: Pure solvent or liquid solution?
Pure solvent always has higher vapour pressure
- Vapour goes from pure solvent to the solution
What is Raoult’s Law and what is it used for?
Psoln = Xsolv (times) Psolv
- Psoln –> observed vapour pressure of soln
- Xsolv –> mole fraction of SOLVENT
–> cuz solv creates pressure (vapour goes from pure solv to soln
- Psolv –> vapour pressure of PURE solvent
–> higher point on graph (linear line)
if Xsolv = 0.5 –> Psoln = 1/2 Psolv
Used to find the vapour pressure of a soln
How to use Raoult’s Law when mixing 2 liquids with 2 different vapour pressures?
Ptotal = PA + PB = XA (times) Psolv A + XB (times) Psolv B
Sum of both linear equations
What is an ideal solution?
When the interaction between 2 liquids is very similar to that of the pure liquid (ideally, straight line between both linear equations on graph)
–> usually, always attraction/repulsion
When do we have a negative deviation?
When there is a strong affinity between two liquids (“like dissolves like”)
–> SOLVENTS LIKE EACH OTHER, so holding on tight
–> vapour pressure is then LOWER than the ideal solution (curves down from straight line)
–> change in energy is exo (delta H)
–> hydrogen bonding
When do we have a positive deviation?
When there is a poor affinity between two liquids
–> SOLVENTS DON’T LIKE EACH OTHER
–> Vapour pressure is then HIGHER than ideal solution (curves up from straight line)
–> change in energy is endo
–> molecules have a higher tendency to escape
