Download colligative properties

COLLIGATIVE PROPERTIES
STATE PERFORMANCE
OBJECTIVES
• Calculate concentration in terms of molality
• Calculate the freezing point depression and
boiling point elevation of a solution. (This
requires determining mole fraction.)
COLLIGATIVE PROPERTIES
• Solute particles may physically alter certain
physical properties of a solution.
• These properties of the solutions will be
different form those of the pure solvent
• these properties are determined by the
number of particles in the solution as
opposed to the type of particles in solutions
Examples
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•
•
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Vapor pressure
freezing point
boiling point
rate of diffusion of the particles through a
membrane ( osmotic pressure)
VAPOR PRESSURE
• EVAPORATION
• vapor - refers to the gaseous state of a
substance that is a liquid or s
• solid at room temperature.
• vapor pressure is the pressure exerted by a
vapor in equilibrium with its liquid
• Volative
• Nonvolative solute
VAPOR PRESSURE
• A solution that contains a nonvolative solute
always has a lower VP than does the pure
solvent
• Dec in VP is directly related to the # of
particles of solute
• If substance dissociates – it has greater
impact on VP than 1 that does not
dissociates
BOILING POINT
• Addition of nonvolative soute to liquid
solvent lowers the VP of the solvent.
• For the liquid to escape as a vapor, it needs
• More kinetic energy
• You see an increase in temperature
FREEZING POINT
• When a substance freezes, the particles take
on an orderly patter
• Solutes disrupts this formation.
• More kinetic energy must be removed from
the solution in order for the solvent to
solidify. The freezing point is lowered.
MOLALITY
• The property of the solution is dependent
upon the number of solute particles present
within a given mass of solvent.
• This makes it more convenient to express
the concentration of the solution in terms of
moles of solution per mass of solvent
• formula
SAMPLE PROBLEM
• If 52 grams of potassium carbonate are
dissolved in 518 grams of water, what is
the molality of the resulting solution?
• homework
RAOULTS’ LAW
• Any nonvolative solute at a specific
concentration lowers the vapor pressure of a
solvent by an amount that is characteristic
of that solvent.
RAOULT’S LAW CONTINUED
• STATES: vapor pressure of a solution
varies directly as the mole fraction of a
solvent.
• To determine the vapor pressure of a
solution, must 1st adjust the vapor pressure
of the pure solvent for the presence of the
solute.
• formula
SAMPLE PROBLEM
• Sugar is extremely soluble in water and is
not a volatile substance. What would the
vapor pressure of water be at 700C if 1.0 x
102 grams of water have dissolved 2 x 102
grams of sucrose?
MOLAL BP Constant
• Kbp
• 1 mole of nonvolatile solute particles will
raise the boiling Temperature of 1 kg of
water by 0.515oC
• Process that is occuring
MOLAL FREEZING POINT
CONSTANT
• Kfp
• 1 mole of nonvolatile solute particles will
lower the freezing point of 1 Kg of water by
1.853oC
• Process
SAMPLE PROBLEM
• If 85 grams of sugar are dissolved in 392
grams of water, what will be the boiling
point and freezing point of the resulting
solution?
IONIC SOLUTIONS
• Will affect the BP and FP of the solutions
• Must adjust for the moles of the ionic
compound because of dissociation
SAMPLE PROBLEM
• If 26.4 grams of nickel(II)bromide are
dissolved in 224 grams of water, what will
be the boiling and freezing point of the
resulting solution. Assume 100% ionization
of the compound.
Determination of the molecular
mass
• Formula
• sample problem
– If 99.0 grams of a nonionizing solute are
dissolved in 669 grams of water and the
freezing point of the resulting solution is
– -0.960oC,what is the molecular mass of the
solute?