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)