properties of solutions
DESCRIPTION
PROPERTIES OF SOLUTIONS. Solution Terms. Solution. A homogeneous mixture of two or more substances in a single phase. Does not have to involve liquids -- air is a solution of nitrogen, oxygen, carbon dioxide etc.; solder is a solution of lead, tin etc. Solute. - PowerPoint PPT PresentationTRANSCRIPT
PROPERTIES OF PROPERTIES OF SOLUTIONSSOLUTIONS
Solution TermsSolution Terms
SolutionSolution
A homogeneous mixture of two or A homogeneous mixture of two or
more substances in a single phase.more substances in a single phase.
Does Does notnot have to involve liquids -- have to involve liquids -- air air
is a solution of nitrogen, oxygen, is a solution of nitrogen, oxygen,
carbon dioxide etc.; solder is a carbon dioxide etc.; solder is a
solution of lead, tin etc.solution of lead, tin etc.
SoluteSolute
Component in lesser Component in lesser concentration.concentration.
““Dissolvee”Dissolvee”
SolventSolvent
Component in greater Component in greater concentration.concentration.
““Dissolver”Dissolver”
SolubilitySolubility
Maximum amount Maximum amount
of material that of material that
will dissolve in a will dissolve in a
given amount of given amount of
solvent at a given solvent at a given
temp. to produce temp. to produce
a stable solution. a stable solution.
Study Solubility Study Solubility Rules!!Rules!!
Saturated SolutionSaturated Solution
A solution containing the A solution containing the maximum maximum
amount of solute that will amount of solute that will dissolve dissolve
under a given set of conditions. under a given set of conditions.
Saturated solutions are at dynamic Saturated solutions are at dynamic
equilibrium with any excess equilibrium with any excess
undissolved solute present. undissolved solute present.
Solute particles dissolve and Solute particles dissolve and
recrystallize at equal rates. recrystallize at equal rates.
This point is the same as This point is the same as solubility solubility
for that substance. for that substance.
Unsaturated SolutionUnsaturated Solution
A solution containing less than the A solution containing less than the
maximum amount of solute that maximum amount of solute that will will
dissolve under a given set of dissolve under a given set of
conditions. conditions.
(more solute can dissolve)(more solute can dissolve)
Supersaturated Supersaturated SolutionSolution
A solution that has been A solution that has been prepared prepared
at an elevated temperature and at an elevated temperature and then slowly cooled. then slowly cooled.
It contains more than the usual It contains more than the usual maximum amount of solution maximum amount of solution dissolved. dissolved.
A supersaturated solution is very A supersaturated solution is very
unstable and the addition of a “seed unstable and the addition of a “seed
crystal’ will cause all excess solute crystal’ will cause all excess solute
to crystallize out of solution leaving to crystallize out of solution leaving
the remaining solvent saturated. the remaining solvent saturated.
(rock candy is made this way) (rock candy is made this way)
MiscibleMiscible
When two or more liquids mix. When two or more liquids mix.
(example: Water and food (example: Water and food coloring) coloring)
ImmiscibleImmiscible
When two or more liquids DON’T When two or more liquids DON’T
mix.--they usually layer if mix.--they usually layer if allowed to allowed to
set for a while. set for a while.
(example: Water and oil) (example: Water and oil)
UNITS OF UNITS OF SOLUTION SOLUTION
CONCENTRATIONCONCENTRATION
Molarity (M)Molarity (M)
# of moles of solute per liter of # of moles of solute per liter of
solution.solution.
ISIS temperature dependent. temperature dependent.
The liquid solvent can expand The liquid solvent can expand and and
contract with changes in contract with changes in
temperature. temperature.
Thus, not a constant ratio of Thus, not a constant ratio of
solute:solvent particles.solute:solvent particles.
Most M solutions are made at Most M solutions are made at 2525 C C
so this point is subtle and so this point is subtle and picky!!picky!!
solution of liters
solute of molesM
Mass Percent Mass Percent (weight percent)(weight percent)
Percent by mass of the solute Percent by mass of the solute in the in the
solution.solution.
100 x solution of grams
solute of grams percent Mass
Mole Fraction (Mole Fraction ())
Ratio of the number of moles of a Ratio of the number of moles of a given given
component to the total number of component to the total number of moles moles
of solution.of solution.
Mole fractionMole fractionaa = = aa
ba
a
nn
n
Molality (m)Molality (m)
# of moles of solute per # of moles of solute per kilogram of kilogram of
solvent.solvent.
NOTNOT temperature dependent. temperature dependent.
Represents a ratio of Represents a ratio of solute:solvent solute:solvent
molecules at all times.molecules at all times.
solvent of kilograms
solute of moles m
Normality (N)Normality (N)
Number of equivalents per liter Number of equivalents per liter of of
solution.solution.
solution of liters
sequivalent N
Equivalent Equivalent (for an acid-base (for an acid-base
reaction) reaction) The mass of acid or base that The mass of acid or base that
can can
furnish or accept exactly one furnish or accept exactly one mole mole
of protons (Hof protons (H++).).
M (# HM (# H++ or OH or OH--) = N) = N
Equivalent Equivalent (for a redox reaction)(for a redox reaction)
The mass of oxidizing or The mass of oxidizing or reducing reducing
agent that can accept or agent that can accept or furnish one furnish one
mole of electrons.mole of electrons.
Exercise 1Exercise 1 Various Various Methods for Describing Methods for Describing Solution Comp.Solution Comp.
A solution is prepared by mixing A solution is prepared by mixing
1.00 g ethanol (C1.00 g ethanol (C22HH55OH) with 100.0 g OH) with 100.0 g water to give a final volume of 101 water to give a final volume of 101
mL. mL.
Calculate the molarity, mass percent, Calculate the molarity, mass percent, mole fraction, and molality of ethanol mole fraction, and molality of ethanol in this solution.in this solution.
SolutionSolution
molarity = 0.215 molarity = 0.215 MM
mass percent = 0.990% mass percent = 0.990% CC22HH55OHOH
mole fraction = 0.00389mole fraction = 0.00389
molality = 0.217molality = 0.217 m m
Exercise 2 Calculating Exercise 2 Calculating Various Methods of Various Methods of Solution Comp. from the Solution Comp. from the MolarityMolarityThe electrolyte in automobile lead The electrolyte in automobile lead
storage batteries is a 3.75 storage batteries is a 3.75 MM sulfuric sulfuric
acid solution that has a density of acid solution that has a density of
1.230 g/mL. Calculate the mass 1.230 g/mL. Calculate the mass
percent, molality, and normality of percent, molality, and normality of
the sulfuric acid.the sulfuric acid.
SolutionSolution
mass percent = 29.9% Hmass percent = 29.9% H22SOSO44
molality = 4.35molality = 4.35 m m
normality is 7.50 normality is 7.50 NN
THE SOLUTION THE SOLUTION PROCESSPROCESS
Energies Involved in Energies Involved in Solution FormationSolution Formation
When a solute is dissolved in a When a solute is dissolved in a
solvent, the attractive forces solvent, the attractive forces
between solute and solvent between solute and solvent particles particles
are great enough to overcome the are great enough to overcome the
attractive forces within the pure attractive forces within the pure
solvent and solute. solvent and solute.
The solute becomes The solute becomes solvatedsolvated
(usually by dipole-dipole or ion-(usually by dipole-dipole or ion-
dipole forces). dipole forces).
When the solvent is water, the When the solvent is water, the
solute is solute is hydratedhydrated..
““Like Dissolves Like”Like Dissolves Like”
Substances with similar types Substances with similar types of of
intermolecular forces dissolve intermolecular forces dissolve in in
each other.each other.
Polar solvents dissolve polar or Polar solvents dissolve polar or ionic ionic
solutes. solutes.
Nonpolar solvents dissolve Nonpolar solvents dissolve nonpolar nonpolar
solutes.solutes.
Water dissolves many salts because Water dissolves many salts because
the strong ion-dipole attractions the strong ion-dipole attractions
that water forms with the ions are that water forms with the ions are
very similar to the strong attractions very similar to the strong attractions
between the ions themselves. between the ions themselves.
The same salts are insoluble in The same salts are insoluble in
hexane (Chexane (C66HH1414) because the weak ) because the weak
LDF forces their ions could form LDF forces their ions could form
with this nonpolar solvent are much with this nonpolar solvent are much
weaker than the attraction between weaker than the attraction between
ions. ions.
Oil does not dissolve in water Oil does not dissolve in water
because the LDF-dipole forces because the LDF-dipole forces are are
much weaker than the much weaker than the hydrogen hydrogen
bonding of water.bonding of water.
Solubilities of Alcohols Solubilities of Alcohols
in Waterin WaterAs the hydrocarbon portion of the As the hydrocarbon portion of the
alcohol increases alcohol increases
in length, the in length, the
alcohol becomes alcohol becomes
less soluble. less soluble.
(More of the (More of the
molecule is nonpolar.)molecule is nonpolar.)
The opposite situation would The opposite situation would exist if exist if
hexane were the solvent.hexane were the solvent.
Heat of Solution Heat of Solution ((HHsolnsoln))
The enthalpy change associated The enthalpy change associated withwith
the formation of a solution.the formation of a solution.
(Just the sum of all of the steps (Just the sum of all of the steps
involved!) involved!)
3 steps:3 steps:
HHsolnsoln = = HH11 + + HH22 + + HH33
HHsolnsoln can be positive can be positive (endothermic) (endothermic)
or negative (exothermic).or negative (exothermic).
Step 1 (Step 1 (HH11))
Breaking up solute (Breaking up solute (endothermicendothermic),),
expanding the solute.expanding the solute.
High in ionic and polar solutes, low High in ionic and polar solutes, low
in nonpolar solutesin nonpolar solutes
HHsolutesolute = - = -HHlattice energylattice energy
Step 2 (Step 2 (HH22))
Breaking up solvent Breaking up solvent ((endothermicendothermic),),
expanding the solvent.expanding the solvent.
High in polar solvent, low in High in polar solvent, low in nonpolar nonpolar
solvent.solvent.
Step 3 (Step 3 (HH33))
Interaction of solute and solvent Interaction of solute and solvent
((exothermicexothermic).).
High negative in polar-polar, low High negative in polar-polar, low
negative in rest.negative in rest.
Enthalpy of Hydration Enthalpy of Hydration
HHhydhyd
HH22 + + HH33
Enthalpy of hydration is more Enthalpy of hydration is more negative for small ions and highly negative for small ions and highly charged ions.charged ions.
Some heats of solution are positive Some heats of solution are positive
(endothermic). The reason that (endothermic). The reason that the the
solute dissolves is that the solution solute dissolves is that the solution
process greatly increases the process greatly increases the
entropy (disorder). This makes the entropy (disorder). This makes the
process spontaneous. process spontaneous.
The solution process involves two The solution process involves two
factors, the change in heat and the factors, the change in heat and the
change in entropy, and their relative change in entropy, and their relative
sizes determine whether a solute sizes determine whether a solute
dissolves in a solvent.dissolves in a solvent.
Hot and Cold PacksHot and Cold Packs
These often consist of a heavy These often consist of a heavy outer pouch containing water and a outer pouch containing water and a thin inner pouch containing a salt. thin inner pouch containing a salt.
A squeeze on the outer pouch A squeeze on the outer pouch breaks the inner pouch and the salt breaks the inner pouch and the salt dissolves. dissolves.
Some hot packs use anhydrous Some hot packs use anhydrous
CaClCaCl22 ( (HHsolnsoln = -82.8 kJ/mol), = -82.8 kJ/mol),
whereas, many cold packs use whereas, many cold packs use
NHNH44NONO33 ( (HHsolnsoln = 25.7 kJ/mol). = 25.7 kJ/mol).
Other hot packs function on the Other hot packs function on the
principle of liquid to solid which is principle of liquid to solid which is
exothermic, while others contain exothermic, while others contain
iron filings and the process of iron filings and the process of
rusting is sped up, thus, rusting is sped up, thus, producing producing
energy.energy.
Exercise 3 Exercise 3 Differentiating Differentiating Solvent Properties Solvent Properties Decide whether liquid hexane Decide whether liquid hexane
(C(C66HH1414) or liquid methanol (CH) or liquid methanol (CH33OH) OH)
is the more appropriate solvent for is the more appropriate solvent for
the substances grease (Cthe substances grease (C2020HH4242) and ) and
potassium iodide (KI).potassium iodide (KI).
SolutionSolution
hexane → greasehexane → grease
methanol → KImethanol → KI
Factors Affecting Factors Affecting SolubilitySolubility
Molecular StructureMolecular Structure
Fat Soluble VitaminsFat Soluble Vitamins
A, D, E, & K -A, D, E, & K - Nonpolar Nonpolar
Can be stored in the body Can be stored in the body tissue tissue
such as fat.such as fat.
Water Soluble Water Soluble VitaminsVitamins
B & C - Polar B & C - Polar
Are not stored, must be Are not stored, must be consumed consumed
regularly.regularly.
HydrophobicHydrophobic
Water fearing Water fearing
NonpolarNonpolar
HydrophilicHydrophilic
Water loving Water loving
PolarPolar
Pressure EffectsPressure Effects
The solubility of a gas is higher The solubility of a gas is higher with with
increased pressure. Pressure has increased pressure. Pressure has
very little effect on the solubility very little effect on the solubility of of
liquids and solids. liquids and solids.
Carbonated beverages must be Carbonated beverages must be
bottled at high pressures to ensure bottled at high pressures to ensure
a high concentration of carbon a high concentration of carbon
dioxide in the liquid.dioxide in the liquid.
Henry’s LawHenry’s Law
The amount of a gas dissolved in a The amount of a gas dissolved in a
solution is directly proportional to solution is directly proportional to
the pressure of the gas above the the pressure of the gas above the
solution.solution.
P= kCP= kC
P = partial pressure of the gaseous P = partial pressure of the gaseous solute above the solution.solute above the solution.
K = constant (depends on the K = constant (depends on the solution).solution).
C = concentration of dissolved C = concentration of dissolved gas. gas.
2
1
2
1
P
P
Solubility
Solubility
Henry’s Law is obeyed best for Henry’s Law is obeyed best for
dilute solutions of gases that dilute solutions of gases that don’t don’t
dissociate or react with the dissociate or react with the solvent.solvent.
Exercise 4Exercise 4Calculations Using Calculations Using Henry’s LawHenry’s Law
A certain soft drink is bottled so A certain soft drink is bottled so that that
a bottle at 25°C contains COa bottle at 25°C contains CO22 gas at gas at
a pressure of 5.0 atm over the a pressure of 5.0 atm over the liquid. liquid.
Assuming that the partial pressure Assuming that the partial pressure
of COof CO22 in the atmosphere is 4.0 X 10 in the atmosphere is 4.0 X 10-4-4
atm, calculate the equilibrium atm, calculate the equilibrium
concentrations of COconcentrations of CO22 in the soda bath in the soda bath
before and after the bottle is opened. before and after the bottle is opened.
The Henry’s law constant for COThe Henry’s law constant for CO22 in in
aqueous solution is 32 L • atm/mol at aqueous solution is 32 L • atm/mol at
25°C.25°C.
SolutionSolution
Before = 0.16 mol/LBefore = 0.16 mol/L
After = 1.2 X 10After = 1.2 X 10-5-5 mol/L mol/L
Temperature EffectsTemperature Effects
The amount of solute that will The amount of solute that will
dissolve usually increases with dissolve usually increases with
increasing temperature. increasing temperature.
Solubility generally increases with Solubility generally increases with
temperature if the solution process temperature if the solution process
is endothermic (is endothermic (HHsolnsoln > 0). > 0).
Solubility generally decreases with Solubility generally decreases with
temperature if the solution process temperature if the solution process
is exothermic (is exothermic (HHsolnsoln < 0). < 0).
Potassium hydroxide, sodium Potassium hydroxide, sodium
hydroxide and sodium sulfate are hydroxide and sodium sulfate are
three compounds that become three compounds that become less less
soluble as the temperature rises. soluble as the temperature rises.
This can be explained by This can be explained by
LeChatelier’s Principle. LeChatelier’s Principle.
Remember, the Remember, the dissolvingdissolving of a solid of a solid
occurs more rapidly with an increase occurs more rapidly with an increase
in temperature, but the in temperature, but the amount of amount of
solidsolid may increase or decrease with may increase or decrease with
an increase in temperature. an increase in temperature.
It is very difficult to predict It is very difficult to predict what what
this solubility may be. this solubility may be. Experimental Experimental
evidence is the only sure way.evidence is the only sure way.
The solubility of The solubility of
a gas in water a gas in water
always always
decreasesdecreases with with
increasing increasing
temperature.temperature.
There are all types of There are all types of environmental environmental
issues involved with the issues involved with the solubility of solubility of
a gas at higher temperatures. a gas at higher temperatures.
Thermal PollutionThermal Pollution
Water being returned to its natural Water being returned to its natural
source at a higher ambient source at a higher ambient
temperature has killed much temperature has killed much wildlife wildlife
as less oxygen is dissolved in the as less oxygen is dissolved in the
water. water.
Boiler ScaleBoiler Scale
Another problem where the coating Another problem where the coating
builds up on the walls of containers builds up on the walls of containers
such as industrial boilers and pipes such as industrial boilers and pipes
causing inefficient heat transfer and causing inefficient heat transfer and
blockage. blockage.
Colligative PropertiesColligative Properties
Properties that depend on the Properties that depend on the
number of dissolved particles -- number of dissolved particles -- not not
on the identity of the particle. on the identity of the particle.
Intermolecular forces of the Intermolecular forces of the solvent solvent
are interrupted when solute is are interrupted when solute is
added. This changes the added. This changes the properties properties
of the solvent. of the solvent.
vapor pressure lowering vapor pressure lowering
boiling point elevationboiling point elevation
freezing point depressionfreezing point depression
osmotic pressureosmotic pressure
These Properties These Properties IncludeInclude
Vapor Pressure Vapor Pressure LoweringLowering
The presence of a nonvolatile solute The presence of a nonvolatile solute
lowers the vapor pressure of a lowers the vapor pressure of a
solvent. This is because the solvent. This is because the dissolved dissolved
nonvolatile solute decreases the nonvolatile solute decreases the
number of solvent molecules per unit number of solvent molecules per unit
volume. (Nonvolatile solute dilutes volume. (Nonvolatile solute dilutes
the solution). the solution).
There are There are
fewer solvent fewer solvent
molecules on molecules on
the surface to the surface to
escape. escape.
This can be mathematically This can be mathematically expressed expressed
by Raoult’s Law:by Raoult’s Law:
PPsolutionsolution = ( = (solventsolvent) ) (P(Poo
solventsolvent))
PPsolutionsolution = observed vapor pressure = observed vapor pressure
of the solvent in the of the solvent in the
solutionsolution
solventsolvent = mole fraction of solvent = mole fraction of solvent
PPoosolventsolvent = vapor pressure of the = vapor pressure of the
pure solventpure solvent
i = van’t Hoff factor (moles of i = van’t Hoff factor (moles of
electrolyte must be multiplied by electrolyte must be multiplied by
this) this)
Number of moles particles in Number of moles particles in
solution/number of moles solution/number of moles particles particles
dissolved.dissolved.
The vapor pressure of a The vapor pressure of a solution is solution is
directly proportional to the directly proportional to the mole mole
fraction of solvent present.fraction of solvent present.
If the solute ionizes, the number of If the solute ionizes, the number of
ions affects vapor pressure. ions affects vapor pressure.
The moles of solute must be The moles of solute must be
multiplied by the number of ions multiplied by the number of ions the the
given solute breaks into. given solute breaks into.
For instance, if we had 1 mole For instance, if we had 1 mole of of
NaCl as the solute, we would NaCl as the solute, we would use 2 use 2
moles of particles for our mole moles of particles for our mole
fraction calculations. fraction calculations.
For nonelectrolytes, i= 1. For nonelectrolytes, i= 1.
For electrolytes, i = the number of For electrolytes, i = the number of
particles formed when one formula particles formed when one formula
unit of the solute dissolves in the unit of the solute dissolves in the
solvent.solvent.
The experimental The experimental
value of i is often value of i is often
less than the less than the
expected value expected value
of i because of of i because of
a phenomenon a phenomenon
called “called “ion pairingion pairing”. ”.
Especially in concentrated Especially in concentrated solutions, solutions,
oppositely charged ions can oppositely charged ions can pair up pair up
and thus, we have fewer and thus, we have fewer particles particles
than expected.than expected.
An An ideal solutionideal solution is a solution that is a solution that
obeys Raoult’s Law. obeys Raoult’s Law.
There is no such thing. There is no such thing.
In very dilute solutions, Raoult’s In very dilute solutions, Raoult’s
Law works fairly well. Solutions are Law works fairly well. Solutions are
most ideal when the solute and the most ideal when the solute and the
solvent are very similar. solvent are very similar.
If hydrogen bonding occurs between If hydrogen bonding occurs between
solute and solvent, vapor pressure is solute and solvent, vapor pressure is
less than expected. We call this a less than expected. We call this a
negative deviation from Raoult’s lawnegative deviation from Raoult’s law. .
This can often be predicted when an This can often be predicted when an
enthalpy of the solution formation is enthalpy of the solution formation is
large and negative (exothermic).large and negative (exothermic).
A great example of this negative A great example of this negative
deviation is acetone and water. deviation is acetone and water.
ExampleExample
Calculate the vapor pressure Calculate the vapor pressure caused caused
by the addition of 100.g of by the addition of 100.g of sucrose, sucrose,
CC1212HH2222OO1111, to 1000.0 g of water if , to 1000.0 g of water if
the vapor pressure of the pure the vapor pressure of the pure
water at 25water at 25°°C is 23.8 torr.C is 23.8 torr.
mol 292.0sucrose g 0.342
sucrose mol 1 x sucrose 100 g
watermol 55.6 waterg 18.0
watermole 1 water x g 1000
PPsolnsoln = 0.995 x 23.8 = 23.7 torr = 0.995 x 23.8 = 23.7 torr
watermol 6.556.55292.0
6.55
water
Exercise 5Exercise 5 Calculating the Vapor Calculating the Vapor Pressure of a SolutionPressure of a SolutionCalculate the expected vapor Calculate the expected vapor
pressure pressure
at 25°C for a solution prepared by at 25°C for a solution prepared by
dissolving 158.0 g of common table dissolving 158.0 g of common table
sugar (sucrose, molar mass = 342.3 sugar (sucrose, molar mass = 342.3
g/mol) in 643.5 cmg/mol) in 643.5 cm33 of water. of water.
At 25°C, the density of water is At 25°C, the density of water is
0.9971 g/cm0.9971 g/cm33 and the vapor and the vapor
pressure is 23.76 torr.pressure is 23.76 torr.
SolutionSolution
= 23.46 torr= 23.46 torr
Exercise 6Exercise 6 Calculating Calculating the Vapor Pressure of a the Vapor Pressure of a Solution Containing Ionic Solution Containing Ionic SoluteSolutePredict the vapor pressure of a Predict the vapor pressure of a
solution prepared by mixing 35.0 g solution prepared by mixing 35.0 g
solid Nasolid Na22SOSO44 (molar mass = 142 (molar mass = 142
g/mol) with 175 g water at 25°C. g/mol) with 175 g water at 25°C.
The vapor pressure of pure water at The vapor pressure of pure water at
25°C is 23.76 torr.25°C is 23.76 torr.
SolutionSolution
= 22.1 torr= 22.1 torr
We can We can
find the find the
molecular molecular
weightweight
of a solute of a solute
by using by using
the vapor the vapor
pressure of pressure of
a solution.a solution.MW
nn
n
P
P
xsolvent
solventsolvent
osolvent
sosolvent
n
g use
nfor solve x
ln
Solutions in which both solute Solutions in which both solute and and
solvent are liquid and the liquids solvent are liquid and the liquids are are
volatile, do not behave ideally. volatile, do not behave ideally.
Both solute and solvent contribute Both solute and solvent contribute
to the vapor pressure.to the vapor pressure.
If the solute is more volatile than If the solute is more volatile than
the solvent, the vapor pressure of the solvent, the vapor pressure of
the solution is higher than the vapor the solution is higher than the vapor
pressure of the solvent. In this case, pressure of the solvent. In this case,
the molecules have a higher the molecules have a higher
tendency to escape than expected. tendency to escape than expected.
We call this a We call this a positive deviation positive deviation
from Raoult’s law.from Raoult’s law.
The enthalpy of solution for this The enthalpy of solution for this
type of deviation is positive. type of deviation is positive.
(endothermic) (endothermic)
00A BBABAtotal PPPPP
(same as Dalton’s Law)
Exercise 7Exercise 7 Calculating Calculating the Vapor Pressure of a the Vapor Pressure of a Solution Containing Two Solution Containing Two LiquidsLiquids
A solution is prepared by mixing A solution is prepared by mixing
5.81 g acetone (C5.81 g acetone (C33HH66O, molar mass O, molar mass = 58.1 g/mol) and 11.9 g chloroform = 58.1 g/mol) and 11.9 g chloroform
(HCCl(HCCl33, molar mass = 119.4 g/mol). , molar mass = 119.4 g/mol). At 35°C, this solution has a total At 35°C, this solution has a total vapor pressure of 260. torr. vapor pressure of 260. torr.
The vapor pressures of pure The vapor pressures of pure acetone acetone
and pure chloroform at 35°C are and pure chloroform at 35°C are 345 345
and 293 torr, respectively.and 293 torr, respectively.
Is this an ideal Is this an ideal solution?solution?
SolutionSolution
Not an ideal solution.Not an ideal solution.
Boiling Point ElevationBoiling Point Elevation
Because vapor pressure is Because vapor pressure is lowered lowered
by the addition of a nonvolatile by the addition of a nonvolatile
solute, boiling point is solute, boiling point is increased. increased.
T = KT = Kbb x m x msolutesolute x i x i
KKbb = molal boiling point elevation = molal boiling point elevation
constant (for water = 0.51 constant (for water = 0.51 C/m)C/m)
i = van’t Hoff factori = van’t Hoff factor
m = concentration in molality m = concentration in molality
T = change in temperature T = change in temperature
Freezing Point Freezing Point DepressionDepression
Freezing is the temperature at Freezing is the temperature at
which the vapor pressure of the solid which the vapor pressure of the solid
and the liquid are equal. If the vapor and the liquid are equal. If the vapor
pressure of the liquid is lowered, the pressure of the liquid is lowered, the
freezing point decreases. This is why freezing point decreases. This is why
NaCl and CaClNaCl and CaCl22 are used on icy roads are used on icy roads
and sidewalks.and sidewalks.
WHY IS A WHY IS A SOLUTION’S SOLUTION’S
FREEZING POINT FREEZING POINT DEPRESSED?DEPRESSED?
Molecules cluster in order to freeze. Molecules cluster in order to freeze.
They must be attracted to one They must be attracted to one
another and have a spot in which to another and have a spot in which to
cluster. Solute molecules get in the cluster. Solute molecules get in the
way! The more ions in solution, the way! The more ions in solution, the
greater the effect on the freezing greater the effect on the freezing
point and the boiling point. point and the boiling point.
A solution does not have a A solution does not have a sharply sharply
defined freezing point. defined freezing point.
Useful for separation purposes in Useful for separation purposes in
fractional crystallization. fractional crystallization.
T = KT = Kff x m x msolutesolute x i x i
KKff = molal freezing point depression = molal freezing point depression
constant (for water = 1.86 C/m) constant (for water = 1.86 C/m)
Add 6 qts. of antifreeze to 12 qts. Add 6 qts. of antifreeze to 12 qts.
cooling system in order to lower the cooling system in order to lower the
FP to -34°F and raise the BP toFP to -34°F and raise the BP to
+226° F.+226° F.
Determining the Molar Determining the Molar
Mass (FW) of a Solution Mass (FW) of a Solution
using Freezing Point using Freezing Point
Depression or Boiling Depression or Boiling
Point ElevationPoint Elevation
Solute concentration must be low Solute concentration must be low
(0.10(0.10mm).).
Disadvantage--compound must be Disadvantage--compound must be
nonvolatile and stable at the boiling nonvolatile and stable at the boiling
point.point.
Still used widely.Still used widely.
Remember that you are looking Remember that you are looking for for
grams/mole!grams/mole!
ExampleExample
Calculate the freezing point and Calculate the freezing point and
boiling point of a solution of boiling point of a solution of 100. g 100. g
ethylene glycol (Cethylene glycol (C22HH66OO22) in 900. ) in 900. g g
of water.of water.
C100.91 point boiling
C0.91 1 x 0.51 x 1.79m T
i x K x m elevation point Boilint
C3.33- point freezing
C3.33 1 x 1.86 x 1.79m T
i x K x m depressionpoint Freezing
m 1.79 kg 090.0
mol 61.1
mol 61.1glycol ethylene g 62.0
glycol ethylene mol 1 x glycol ethylene g 100
b
b
f
f
m
Exercise 8Exercise 8Calculating the Molar Calculating the Molar Mass by Boiling-Point Mass by Boiling-Point ElevationElevation
A solution was prepared by A solution was prepared by dissolving dissolving
18.00 g glucose in 150.0 g water. 18.00 g glucose in 150.0 g water.
The resulting solution was found The resulting solution was found to to
have a boiling point of 100.34°C. have a boiling point of 100.34°C.
Calculate the molar mass of Calculate the molar mass of
glucose. glucose.
Glucose is a molecular solid that is Glucose is a molecular solid that is
present as individual molecules in present as individual molecules in
solution.solution.
SolutionSolution
= 180 g/mol= 180 g/mol
Exercise 9Exercise 9 Freezing-Freezing- Point Depression Point Depression
What mass of ethylene glycol (CWhat mass of ethylene glycol (C22HH66OO22, ,
molar mass = 62.1 g/mol), the main molar mass = 62.1 g/mol), the main
component of antifreeze, must be component of antifreeze, must be added added
to 10.0 L water to produce a solution for to 10.0 L water to produce a solution for
use in a car’s radiator that freezes at use in a car’s radiator that freezes at
-10.0°F (-23.3°C)? Assume the density -10.0°F (-23.3°C)? Assume the density
of water is exactly 1 g/mL.of water is exactly 1 g/mL.
SolutionSolution
= 7.76 X 10= 7.76 X 1033 g (or 7.76 kg) g (or 7.76 kg)
Exercise 10 Exercise 10 Determining Molar Determining Molar Mass by Freezing-Mass by Freezing-Point DepressionPoint DepressionA chemist is trying to identify a A chemist is trying to identify a
human hormone, which human hormone, which controls controls
metabolism, by determining its metabolism, by determining its
molar mass. molar mass.
A sample weighing 0.546 g was A sample weighing 0.546 g was dissolved in 15.0 g benzene, and dissolved in 15.0 g benzene, and the freezing-point depression was the freezing-point depression was determined to be 0.240° C. determined to be 0.240° C.
Calculate the molar mass of the Calculate the molar mass of the hormone.hormone.
SolutionSolution
= 776 g/mol= 776 g/mol
OSMOTIC OSMOTIC PRESSUREPRESSURE
Semipermeable Semipermeable MembraneMembrane
Membrane which Membrane which
allows solvent but allows solvent but
not solute molecules not solute molecules
to pass through to pass through
(small molecules (small molecules can can
pass but large ones pass but large ones
cannot).cannot).
OsmosisOsmosis
The passage of solvent into solution The passage of solvent into solution
through a semipermeable through a semipermeable membrane. membrane.
Osmosis occurs when solvent Osmosis occurs when solvent
molecules move through a molecules move through a
semipermeable membrane from a semipermeable membrane from a
region of lower solute region of lower solute concentration concentration
to a region of higher solute to a region of higher solute
concentration. It is driven by the concentration. It is driven by the
need nature has to establish an need nature has to establish an
equilibrium.equilibrium.
Osmotic Pressure-(Osmotic Pressure-())
The pressure that must be The pressure that must be applied applied
to a solution to prevent the net to a solution to prevent the net movement of water from movement of water from
solvent to solvent to solution (osmosis). solution (osmosis).
The osmotic pressure of a The osmotic pressure of a solution is solution is
proportional to the number of proportional to the number of solute solute
particles in a given volume of particles in a given volume of
solution, that is, to the molarity. solution, that is, to the molarity.
The equation is similar to the The equation is similar to the ideal ideal
gas law since both relate the gas law since both relate the
pressure of a system to its pressure of a system to its
concentration and temperature.concentration and temperature.
= MRTi or = MRTi or = = nRTnRT x i x i VV
= osmotic pressure in atm= osmotic pressure in atmM = molarity of the solutionM = molarity of the solutionR = 0.08206 L-atm/K-molR = 0.08206 L-atm/K-molT = temperature in KelvinT = temperature in Kelvini = van’t Hoff factori = van’t Hoff factor
The use of osmotic pressure The use of osmotic pressure
calculations for determining the calculations for determining the
molecular mass of an unknown molecular mass of an unknown
substance is more accurate than the substance is more accurate than the
use of freezing point depression or use of freezing point depression or
boiling point elevation data because boiling point elevation data because a a
small concentration of solute small concentration of solute
produces a relatively large osmotic produces a relatively large osmotic
pressure.pressure.
Ideal for measuring molar Ideal for measuring molar masses masses
of large molecules of biological of large molecules of biological
importance.importance.
ExampleExample
The concentration of The concentration of hemoglobin in hemoglobin in
blood is roughly 15g/100mL of blood is roughly 15g/100mL of
solution. solution.
Assume that a solution contains 15g Assume that a solution contains 15g
of hemoglobin dissolved in water to of hemoglobin dissolved in water to
make 100 mL of solution and that make 100 mL of solution and that
the osmotic pressure of this solution the osmotic pressure of this solution
is found to be 0.050 atm at 25is found to be 0.050 atm at 25°°C.C.
What is the molecular mass of What is the molecular mass of
hemoglobin? hemoglobin?
(The osmotic pressure of a 1 m (The osmotic pressure of a 1 m
solution at 25solution at 25°°C is 24.45 atm.)C is 24.45 atm.)
molgMW /73400050.0
)298)(08206.0(1.0
15
dRT MW or
V
nRT
Exercise 11 Exercise 11 Determining Molar Determining Molar Mass from Osmotic Mass from Osmotic PressurePressureTo determine the molar mass of a To determine the molar mass of a
certain protein, 1.00 X 10certain protein, 1.00 X 10-3-3 g of it g of it
was dissolved in enough water to was dissolved in enough water to
make 1.00 mL of solution. make 1.00 mL of solution.
The osmotic pressure of this The osmotic pressure of this
solution was found to be 1.12 torr solution was found to be 1.12 torr
at 25.0°C. at 25.0°C.
Calculate the molar mass of the Calculate the molar mass of the
protein.protein.
SolutionSolution
= 1.66 X 10= 1.66 X 1044 g/mol g/mol
Exercise 12Exercise 12 Isotonic Isotonic Solutions Solutions
What concentration of sodium What concentration of sodium
chloride in water is needed to chloride in water is needed to
produce an aqueous solution produce an aqueous solution
isotonic with blood (isotonic with blood ( = 7.70 = 7.70 atm at atm at
25°C)?25°C)?
SolutionSolution
= 0.158 = 0.158 MM
Exercise 13Exercise 13 Osmotic Pressure Osmotic Pressure
The observed osmotic pressure The observed osmotic pressure for for
a 0.10 a 0.10 MM solution of Fe(NH solution of Fe(NH44))22(SO(SO44))22 at 25°C is 10.8 atm. at 25°C is 10.8 atm.
Compare the expected and Compare the expected and experimental values forexperimental values for i. i.
SolutionSolution
Expected = 5Expected = 5
Experimental = 4.4Experimental = 4.4
APPLICATIONS OF APPLICATIONS OF OSMOSISOSMOSIS
DialysisDialysis
A phenomenon in which a A phenomenon in which a
semipermeable membrane semipermeable membrane allows allows
transfer of both solvent transfer of both solvent molecules molecules
and small solute molecules and and small solute molecules and
ions. Occurs in walls of most ions. Occurs in walls of most
plant and animal cells.plant and animal cells.
Kidney dialysis Kidney dialysis is one of most is one of most important important applications. applications. Waste Waste molecules move into the “wash” molecules move into the “wash” solution and filter the blood.solution and filter the blood.
Isotonic SolutionIsotonic Solution
Solutions that have the same Solutions that have the same
osmotic pressure. (Ex. IV fluids)osmotic pressure. (Ex. IV fluids)
HypertonicHypertonic
Solution has Solution has
higher osmotic higher osmotic
pressure (cells pressure (cells
bathed in a hypertonic solution bathed in a hypertonic solution
would shrivel –crenation). Treating would shrivel –crenation). Treating
the surface of food with salt causes the surface of food with salt causes
this to happen to bacteria. this to happen to bacteria.
HypotonicHypotonic
Solution has Solution has
lower osmotic lower osmotic
pressure (cells pressure (cells
bathed in a bathed in a
hypotonic hypotonic
solution would solution would
burst—hemolysis). burst—hemolysis).
Reverse OsmosisReverse Osmosis
The process occurring when the The process occurring when the
high external pressure on a high external pressure on a solution solution
causes a net flow of solvent causes a net flow of solvent through through
a semipermeable membrane from a semipermeable membrane from
the solution to the solvent.the solution to the solvent.
Used in desalination Used in desalination
(the membrane here (the membrane here
acts as a “molecular acts as a “molecular
filter” to remove filter” to remove
solute particles). The need for this solute particles). The need for this
process will probably increase as process will probably increase as the the
need for drinkable water increases. need for drinkable water increases.
Colloids (also called Colloids (also called Colloidal Dispersions) Colloidal Dispersions)
Thomas Graham, 1860--albumin, Thomas Graham, 1860--albumin,
starch, gelatin and glue diffuse starch, gelatin and glue diffuse only only
very slowly and could not be very slowly and could not be
crystallized. He called these crystallized. He called these
substances colloids.substances colloids.
““A suspension of tiny particles A suspension of tiny particles
in some medium.”in some medium.”
The dispersed colloidal particles The dispersed colloidal particles are are
larger than a simple molecule larger than a simple molecule but but
small enough to remain small enough to remain distributed distributed
and not settle out. and not settle out.
A colloidal particle has a A colloidal particle has a diameter diameter
between 1 and 1000 nm and between 1 and 1000 nm and may may
contain many atoms, ions, or contain many atoms, ions, or
molecules. molecules.
Because of their small particle Because of their small particle size, size,
colloids have an enormous total colloids have an enormous total
surface area.surface area.
The particles stay suspended The particles stay suspended
because of electrostatic because of electrostatic repulsion. repulsion.
Hydrophobic/Hydrophilic endsHydrophobic/Hydrophilic ends
Coagulation, destruction of a Coagulation, destruction of a colloid, colloid,
occurs by heating (particles collide occurs by heating (particles collide so so
hard that they stick together) or hard that they stick together) or by by
the addition of an electrolyte the addition of an electrolyte (neutralizes ion layers). (neutralizes ion layers).
This process is This process is
important in important in
removal of soot removal of soot
from smoke so from smoke so
that air quality that air quality
has improved has improved
somewhat in somewhat in
industrialized cities.industrialized cities.
Tyndall EffectTyndall Effect
The scattering of light by particles.The scattering of light by particles.
Used to distinguish between a Used to distinguish between a
suspension and a true solution. suspension and a true solution.
A true solution has particles that A true solution has particles that are are
too small to scatter light.too small to scatter light.
Brownian MotionBrownian Motion
A characteristic movement in A characteristic movement in which which
the particles change speed and the particles change speed and
direction erratically (solvent direction erratically (solvent
molecules collide with the molecules collide with the colloidal colloidal
particles).particles).
SuspensionsSuspensions are temporary are temporary
solutions. They will settle eventually. solutions. They will settle eventually.
Colloids will not do this. Colloids will not do this.
SolutionsSolutions are permanent. Particles are permanent. Particles
are really small. Colloids lie in are really small. Colloids lie in
between solutions and suspensions!between solutions and suspensions!
Examples of Some Examples of Some Common ColloidsCommon Colloids
Foam- colloidal dispersion of a gas Foam- colloidal dispersion of a gas
dispersed in a liquid or solid (ex. dispersed in a liquid or solid (ex.
Whipped cream and marshmallows)Whipped cream and marshmallows)
Aerosol- colloidal dispersion of a Aerosol- colloidal dispersion of a
liquid or solid dispersed in a gas (ex. liquid or solid dispersed in a gas (ex.
Fog and smoke)Fog and smoke)
Emulsion- colloidal dispersion of a Emulsion- colloidal dispersion of a
liquid dispersed in a solid or liquid liquid dispersed in a solid or liquid
(ex. Butter and milk)(ex. Butter and milk)
Solution- colloidal dispersion of a Solution- colloidal dispersion of a
solid dispersed in a liquid or solid solid dispersed in a liquid or solid
(ex. Paint or ruby)(ex. Paint or ruby)