Lecture 4 Flashcards
What are colligative properties and what are some examples?
Properties that depend only on the number and NOT identity of solute particles in an ideal solution
–> don’t matter on identity/structure of compound
EX: boiling pt, freezing pt, depression, osmotic pressure
At what pressure does a solution boil and why do we add salt to solutions when cooking
Boils at 1 atm (boils to get to 1 atm)
Adding salt lower the pressure the solution has to get to boil (from 1 to 0.9 atm)
–> salt lower vapour pressure of soln, so higher temp must be reached to make soln vapour pressure = 1atm
What is the boiling point elevation equation?
delta(T)b = Kb (times) msolt
- delta(T) –> difference between boiling point of soln and pure solv
- Kb – molal boiling-point elevation constant
- msol –> molality of solute
NOTE: delta(T)b = bp soln - bp pure solv
What is the freezing point elevation equation?
delta(T)f = Kf (times) msolt
- delta(T) –> difference between freezing point of pure solv and soln
- Kb – molal freezing-point elevation constant
- msol –> molality of solute
NOTE: delta(T)f = fp pure solv - fp soln
What is osmotic pressure? (theory)
Amount of pressure applied (by soln) to bring 2 levels equal
–> Adding solt to solv increases the solv’s osmotic pressure (pressure created by solution)
–> Water goes in through membrane to decrease concentration of soln (dilute salt)
–> Equal to pressure applied a piston preventing osmosis (needed to stop osmosis)
(Osmosis: process of moving solvent)
What is osmotic pressure? (equation)
pi = MRT
- pi –> osmotic pressure in atm
- M –> molarity of soln
- R –> gas law constant (0.08206 Latm/Kmol)
What is an example of the use of osmotic pressure?
Principle behind DIALYSIS (process when kidney stops working and so, you take out impurities)
–> blood is cleaned using isotonic solution(same concentration of electrolytes as blood cells) to remove waste products
–> here, solute can cross membrane though
