Solutions Flashcards
Components
minimum number of independent species necessary to define the composition of all phases in a system
Phase diagram
Plot of pressure vs temperature
Phase boundary
Continuous line representing values at which equilibrium exists between 2 phases
Triple point
Point at which 3 phases coexist at equilibrium
What is different about water phase diagram?
Solid/Liquid line leans towards the y-axis.
Why is the water phase diagram different?
The solid/liquid line leans towards the y-axis due to being less dense in the solid phase than liquid phase. This is due to H bonding and oxygen repelling other oxygens
Degrees of Freedom
Number of factors which can be varied independently without altering the number of phases
Gibbs Phase Rule in condensed systems
P+F = C+1
Gibbs Phase Rule
P+F = C+2
Colligative Properties
4 physical properties affected in the same way by solutes, regardless of solute identity
What do Colligative Properties depend on?
Properties of solvent, concentration of dissolved substance and number of particles of dissolved substance in the solution
How are the colligative properties related?
Thermodynamically
What are the 4 main Colligative Properties?
Vapour Pressure lowering, Freezing point depression, boiling point elevation and osmotic pressure
Osmosis
The tendency of solvent molecules to pass through a membrane from a more dilute to a more concentrated solution.
Osmotic pressure
If a solution is separated from its solvent by a membrane then the excess pressure which has to be applied to prevent the flow of the solvent is the osmotic pressure
Osmotic pressure equation
Π = mRT
Semi-permeable membrane
Chemical potential of a solvent in solution is less than its chemical potential in a pure solvent. Solvent passes spontaneously into the solution to equalise the chemical potential on either side of the membrane
Reverse Osmosis
A pressure greater than the osmotic pressure is applied to the solution and forces the solvent through the membrane
Hydrostatic pressure
Pressure exerted by a column of aqueous solution
Iso-osmotic
2 solutions have the same osmotic pressure
Isotonic
2 solutions have the same solute concentration
If osmotic pressure is hypotonic, what happens to cells?
They swell
If osmotic pressure is hypertonic, what happens to cells?
They shrink
What is the osmotic pressure of blood?
291 m osmol dm-3
Osmolality
The mass of solute which when dissolved in 1kg of water will exert an osmotic pressure equal to that exerted by 1 mol of an ideal and unionised substance dissolved in 1kg of water
Osmol
A mole of a substance that is non-dissociable in a solution
Freezing point depression of blood
ΔTf = 0.52°C
Freezing point depression
Freezing point depression is the lowering of the freezing point of a solvent by adding a non-volatile solute
Equation for freezing point depression
ΔTf = Kf x m
Osmotic pressure equation using ΔTf
Π = ΔTf/Kf x RT
What is W = 0.52-a / b used for?
When it is not possible to adjust the concentration of a drug to make it more isotonic with blood, an adjusting substance can be added.
W = weight of adjusting substance per 100cm3
a= ΔTf of drug solution
b = ΔTf produced by 1%w/v of adjusting substance
Solubility of gas in a liquid
The concentration of the dissolved gas when it is at equilibrium with some of the pure gas above the solution
Henry’s Law
The vapour pressure exerted by a gas dissolved in a solvent at constant temperature is proportional to the mole fraction of the gas
Henry’s Law equation
pB = kH + xB
xB = mole fraction of the gas
pB = vapour pressure of the gas
kH = Henry’s Law constant
What happens to gas solubility as temperature increases?
Gas solubility decreases due to the greater tendency of gas to expand
Salting out
Liberation of gas from a solution by the addition of NaCl or sucrose. The added solute attracts water molecules, reducing the density of the aqueous environment adjacent to the gas molecules
Degrees of Freedom in an immiscible solution
2 degrees of freedom
Degrees of Freedom in a miscible solution
3 degrees of freedom
Upper Critical Solution temperature
Highest temperature at which phase seperation occurs. This is due to thermal motion overcoming potential energy advantage of one type of molecule being close together
Lower critical solution temperature
Temperature at which they mix in all proportions and above which they form 2 products. More miscible at low temperatures as a weak complex is formed
Phase diagram point B
The eutectic point - the lowest temperature at which liquid solution can exist
Raoult’s Law
Applies to solvent in solution
Raoult’s Law equation
pA = p°A xA
p°A is the vapour pressure of pure solvent
pA is the vapour pressure of solvent in solution
xA is the mole fraction of the solvent
Mole fraction in Henry’s and Raoult’s law
xB = 1 - xA
What solutions obey Raoult’s law?
Ideal solutions
How are non-ideal solutions formed?
Formed in the process of mixing of components and is accompanied by absorption of heat
Theory of colloid stability
DLVO
Total Vapour Pressure
pTotal = pA + pB
Total potential energy using DLVO theory
vTotal = vA (attractive potential energy) + vR (Electrostatic repulsive energy)
Low electrolyte concentration on DLVO plot
High primary maximum and no secondary minimum
High electrolyte concentration on DLVO plot
No primary maximum or secondary minimum
