SolutionsSolutions

Occur in all phasesOccur in all phases The solvent does the dissolving, The solvent does the dissolving,

usually is the substance that is usually is the substance that is present in the greatest amount.present in the greatest amount.

The solute is dissolved.The solute is dissolved. There are examples of all types of There are examples of all types of

solutes dissolving all types of solvent solutes dissolving all types of solvent (9 types).(9 types).

We will focus on aqueous solutions.We will focus on aqueous solutions.

Formation of a SolutionFormation of a Solution

When 1 or more substances disperses When 1 or more substances disperses uniformly throughout a solution.uniformly throughout a solution.

We talked about intermolecular We talked about intermolecular forces, they can also exist between forces, they can also exist between solute and the solvent particles in a solute and the solvent particles in a solution. solution.

For example, If you were to dissolve For example, If you were to dissolve solid KCl in water, it would readily solid KCl in water, it would readily dissolve because the attractive dissolve because the attractive interactions between the ions and theinteractions between the ions and the

Polar water molecules are strong and Polar water molecules are strong and overcome the lattice energy holding overcome the lattice energy holding KCl together. The force of the ion-KCl together. The force of the ion-dipole attraction is strong enough to dipole attraction is strong enough to pull the ions out of the crystalline pull the ions out of the crystalline structure.structure.

Solvation, when the particles of the Solvation, when the particles of the solute are completely surrounded by solute are completely surrounded by the solvent. (called hydration when the solvent. (called hydration when the solvent is water)the solvent is water)

Forming a solutionForming a solution

To form a solution, not only do we To form a solution, not only do we need to break apart the bond (NaCl), need to break apart the bond (NaCl), but between water molecules also so but between water molecules also so there is room for the ions to fit in.there is room for the ions to fit in.

The enthalpy change is made of 3 The enthalpy change is made of 3 energies.energies.

ΔΔHHsolnsoln= = ΔΔHH11 + + ΔΔHH22 + + ΔΔHH3 3

Energy of Making SolutionsEnergy of Making Solutions Heat of solution ( Heat of solution ( HHsoln soln ) is the ) is the

energy change for making a energy change for making a solution.solution.

Most easily understood if broken Most easily understood if broken into steps.into steps.

1.Break apart solvent 1.Break apart solvent 2.Break apart solute2.Break apart solute 3. Mixing solvent and solute3. Mixing solvent and solute

1. Break apart Solvent1. Break apart Solvent Have to overcome attractive forces. Have to overcome attractive forces.

HH11 >0 >0

2. Break apart Solute.2. Break apart Solute. Have to overcome attractive forces. Have to overcome attractive forces.

HH22 >0 >0

3. Mixing solvent and 3. Mixing solvent and solutesolute

HH3 3 depends on what you are mixing.depends on what you are mixing.

If the molecules are attracted to each If the molecules are attracted to each other other HH3 3 is large and negative (ion is large and negative (ion dipole).dipole).

If the molecules are not attracted to each If the molecules are not attracted to each other, then other, then HH3 3 isis small and negative (non small and negative (non polar solute- polar solvent).polar solute- polar solvent).

Exothermic/ EndothermicExothermic/ Endothermic

When calculating the enthalpy of When calculating the enthalpy of solution, the sum can be + or -, solution, the sum can be + or -, depending on substances.depending on substances.

(-) exothermic, the solution would get (-) exothermic, the solution would get warmerwarmer

(+) endothermic, the solution would (+) endothermic, the solution would get colderget colder

Energy

Reactants

Solution

H1

H2

H3

Solvent

Solute and Solvent

Size of Size of HH33 determines whether a determines whether a solution will formsolution will form

H3

Solution

Ice packs, heat packsIce packs, heat packs

(-) heat of solution, solution gets (-) heat of solution, solution gets warmwarm

(+) heat of solution, the solution gets (+) heat of solution, the solution gets coolcool

SpontaneitySpontaneity

Exothermic processes are usually Exothermic processes are usually spontaneousspontaneous

A solution will not form if it is too A solution will not form if it is too endothermic.endothermic.

NaCl would not dissolve in gasoline, NaCl would not dissolve in gasoline, gasoline is non-polar, and the weak gasoline is non-polar, and the weak forces you would get between the forces you would get between the non-polar gas and NaCl would not be non-polar gas and NaCl would not be enough energy to break apart the enough energy to break apart the bond in NaClbond in NaCl

Like dissolves LikeLike dissolves Like

That’s where this saying came from.That’s where this saying came from. In order to understand it, you must In order to understand it, you must

understand the relative strength of understand the relative strength of bonds.bonds.

When non-polar substances are When non-polar substances are mixed, they are all London mixed, they are all London Dispersion Forces, so there is no net Dispersion Forces, so there is no net energy change, however this is also energy change, however this is also a spontaneous process?a spontaneous process?

There must be something besides There must be something besides energy then that accounts for energy then that accounts for whether a reaction will proceed whether a reaction will proceed spontaneously or not. Two things: spontaneously or not. Two things: Enthalpy and EntropyEnthalpy and Entropy

Types of Solvent and Types of Solvent and solutessolutes

If If HHsolnsoln is small and positive, a is small and positive, a solution will still form because of solution will still form because of entropy.entropy.

There are many more ways for them There are many more ways for them to become mixed than there is for to become mixed than there is for them to stay separate.them to stay separate.

SpontaneitySpontaneity

Two ways a reaction will proceed Two ways a reaction will proceed spontaneously:spontaneously:

1) Exothermic processes are usually 1) Exothermic processes are usually spontaneous, the change tends to spontaneous, the change tends to lower the energy of the systemlower the energy of the system

2) Processes in which the disorder of 2) Processes in which the disorder of the system increases also tend to the system increases also tend to occur spontaneously.occur spontaneously.

In sumIn sum

The formation of solutions is favored The formation of solutions is favored by an increase in disorder. A solution by an increase in disorder. A solution will form unless the solute-solute or will form unless the solute-solute or solvent-solvent interactions are too solvent-solvent interactions are too strong compared to the solute-strong compared to the solute-solvent interactions.solvent interactions.

Physical / Chemical Physical / Chemical SolutionsSolutions

Be careful to distinguish whether the Be careful to distinguish whether the formation of a solution is chemical or formation of a solution is chemical or physical. If you can recover the physical. If you can recover the original substance, than it is a original substance, than it is a physical change (dissolving in water).physical change (dissolving in water).

Structure and SolubilityStructure and Solubility Water soluble molecules must have Water soluble molecules must have

dipole moments -polar bonds.dipole moments -polar bonds. To be soluble in non polar solvents To be soluble in non polar solvents

the molecules must be non polar.the molecules must be non polar.

Saturated SolutionsSaturated Solutions

When a solution is in contact with an When a solution is in contact with an undissolved solute, two opposing undissolved solute, two opposing reactions are occurring, dissolving, reactions are occurring, dissolving, and crystallization.and crystallization.

When the rate is equal, equilibrium is When the rate is equal, equilibrium is established, there is no further established, there is no further increase in the amount of solute that increase in the amount of solute that will dissolve.will dissolve.

The system is said to be saturatedThe system is said to be saturated Adding more solute to the system Adding more solute to the system

will not result in an increase in the will not result in an increase in the concentration of the solution, the concentration of the solution, the solute particles will remain solute particles will remain undissolved undissolved

The amount of solute needed to form The amount of solute needed to form a saturated solution in a given a saturated solution in a given quantity of solvent is known as the quantity of solvent is known as the solubility of that solvent. solubility of that solvent.

Unsaturated solutions have the Unsaturated solutions have the capacity to hold more solutecapacity to hold more solute

Supersaturated solutions are Supersaturated solutions are sometimes possible to form. When sometimes possible to form. When dissolve the substance in hot solvent dissolve the substance in hot solvent and cool it, all of the solute may and cool it, all of the solute may remain dissolved even though the remain dissolved even though the solubility has decreased with the solubility has decreased with the decrease in temp. decrease in temp.

Supersaturated solutions Supersaturated solutions

Extremely unstableExtremely unstable Adding a seed crystal will result in Adding a seed crystal will result in

the excess solute crystallizing out of the excess solute crystallizing out of the solution.the solution.

Factors affecting solubilityFactors affecting solubility

Natural tendency to move towards Natural tendency to move towards disorderdisorder

Attraction between solute and Attraction between solute and solvent, the stronger the attraction solvent, the stronger the attraction between solute and solvent, the between solute and solvent, the greater the solubility of the solute in greater the solubility of the solute in that substance. that substance.

Miscible/ immiscibleMiscible/ immiscible

Liquids that mix in all proportions are Liquids that mix in all proportions are said to be misciblesaid to be miscible

Liquids that do not mix are Liquids that do not mix are immiscibleimmiscible

(Hydrocarbons do not mix in water)(Hydrocarbons do not mix in water)

Solubility of alcohol in waterSolubility of alcohol in water

Alcohols have the OH end which is polarAlcohols have the OH end which is polar Solubility of alcohols decrease with Solubility of alcohols decrease with

increasing mass because the chain is increasing mass because the chain is becoming more like a hydrocarbonbecoming more like a hydrocarbon

However if the number of OH groups However if the number of OH groups increases, the solubility will increaseincreases, the solubility will increase

Network solids are not soluble in either Network solids are not soluble in either polar or non polar solvents because of the polar or non polar solvents because of the strong bonding forces within the solidstrong bonding forces within the solid

Pressure effectsPressure effects Changing the pressure doesn’t effect Changing the pressure doesn’t effect

the amount of solid or liquid that the amount of solid or liquid that dissolvesdissolves

They are incompressible.They are incompressible. It does effect gases, the solubility of It does effect gases, the solubility of

a gas in any solvent is increased as a gas in any solvent is increased as the pressure over the gas is the pressure over the gas is increased.increased.

Dissolving GasesDissolving Gases Pressure effects the Pressure effects the

amount of gas that amount of gas that can dissolve in a can dissolve in a liquid.liquid.

The dissolved gas is The dissolved gas is at equilibrium with at equilibrium with the gas above the the gas above the liquid.liquid.

The gas is at The gas is at equilibrium with the equilibrium with the dissolved gas in this dissolved gas in this solution.solution.

The equilibrium is The equilibrium is dynamic.dynamic.

If you increase the If you increase the pressure the gas pressure the gas molecules dissolve molecules dissolve faster.faster.

The equilibrium is The equilibrium is disturbed.disturbed.

The system reaches The system reaches a new equilibrium a new equilibrium with more gas with more gas dissolved.dissolved.

Henry’s Law.Henry’s Law.

P= kCP= kC

Pressure = constant x Pressure = constant x

Concentration Concentration of gas of gas

TryTry

Calculate the concentration of COCalculate the concentration of CO22 in in a soft drink that is bottled with a a soft drink that is bottled with a partial pressure of 2.0 atm over the partial pressure of 2.0 atm over the liquid at 25°C. The Henry’s law liquid at 25°C. The Henry’s law constant for COconstant for CO22 in water at this in water at this temperature is 3.1 x 10temperature is 3.1 x 10-2 -2

mol/L-atm.mol/L-atm.

Temperature EffectsTemperature Effects Increased temperature increases the Increased temperature increases the

rate at which a solid dissolves.rate at which a solid dissolves. Usually it will increase the amount of Usually it will increase the amount of

solid that dissolves.solid that dissolves.

20 40 60 80 100

Gases are predictableGases are predictable

As temperature As temperature increases, solubility increases, solubility decreases.decreases.

Gas molecules can Gas molecules can move fast enough to move fast enough to escape.escape.

ConcentrationConcentration

Dilute- small concentration of soluteDilute- small concentration of solute

Concentrate-large concentration of Concentrate-large concentration of solidsolid

1. Quantitatively1. Quantitatively

Mass percentage = Mass percentage = mass solute mass solute x 100x 100 mass solutionmass solutionVery dilute in ppm = Very dilute in ppm = mass solute mass solute x 10x 1066

mass solutionmass solutionA solution of 1 ppm = 1g/ million gA solution of 1 ppm = 1g/ million g Really dilute ppb= Really dilute ppb= mass solutemass solute x 10 x 1099

mass solutionmass solution

2. Mole Fraction2. Mole Fraction

Moles component Moles component

total moles of all componentstotal moles of all components

Useful when dealing with gasesUseful when dealing with gases

3. Molarity3. Molarity

Molarity = Molarity = moles of solutemoles of solute

liters of solutionliters of solution

Molality = Molality = moles of solute moles of solute Kilograms of solvent Kilograms of solvent

Molarity changes with Molarity changes with temperature, molality does not.temperature, molality does not.

Usually use molality when a Usually use molality when a solution is to be used over a range solution is to be used over a range of temperatures.of temperatures.

4. Molality4. Molality

ProblemsProblems

Calculate the mass percentage of NaCalculate the mass percentage of Na22SOSO44 in a in a solution containing 14.7 g of Nasolution containing 14.7 g of Na22SOSO44 dissolved dissolved in 345 g of water. in 345 g of water.

Calculate the mole fraction of methanol Calculate the mole fraction of methanol (CH(CH33OH) when 7.5 grams of it is dissolved in OH) when 7.5 grams of it is dissolved in 245 g of water.245 g of water.

Calculate the molarity of a solution when 10.5 Calculate the molarity of a solution when 10.5 g of KCL is dissolved in 250 ml of solution.g of KCL is dissolved in 250 ml of solution.

Calculate the molality of a solution when 13 g Calculate the molality of a solution when 13 g of benzene (Cof benzene (C66HH66) is dissolved in 17 g of CCl) is dissolved in 17 g of CCl44. .

Colligative properties Colligative properties

Add ethylene glycol to car radiators Add ethylene glycol to car radiators as antifreezeas antifreeze

Add salt to water to lower the Add salt to water to lower the freezing pointfreezing point

Also raises the boiling point.Also raises the boiling point. Reduces the vapor pressureReduces the vapor pressure Reduces osmotic pressureReduces osmotic pressure

Colligative PropertiesColligative Properties

Colligative properties depend only on Colligative properties depend only on the number - not the kind of solute the number - not the kind of solute particles presentparticles present

Vapor PressureVapor Pressure

Vapor pressure is the pressure Vapor pressure is the pressure exerted by a gas above the liquid in exerted by a gas above the liquid in a closed system at equilibriuma closed system at equilibrium

A non-volatile substance has no A non-volatile substance has no appreciable vapor pressureappreciable vapor pressure

A volatile substance wouldA volatile substance would

Vapor Pressure of Vapor Pressure of SolutionsSolutions

A nonvolatile solute lowers the vapor A nonvolatile solute lowers the vapor pressure of the solution.pressure of the solution.

Raoult’s Law:Raoult’s Law:PPsolnsoln = = solvent solvent x Px Psolventsolvent Vapor pressure of the solution = Vapor pressure of the solution =

mole fraction of solvent xmole fraction of solvent x vapor vapor pressure of the pure solventpressure of the pure solvent

Doesn’t depend on the type of particle, Doesn’t depend on the type of particle, only the concentration. Also, only only the concentration. Also, only works with non-volatile solutes works with non-volatile solutes otherwise they would be contributing to otherwise they would be contributing to the pressure. (assume non-electrolytes)the pressure. (assume non-electrolytes)

Real SolutionsReal Solutions

Raoult’s Law- for ideal solutionsRaoult’s Law- for ideal solutions A solution only approaches ideal A solution only approaches ideal

conditions when the solute conditions when the solute concentration is low, and when the concentration is low, and when the solute and solvent have similar solute and solvent have similar molecular sizes and intermolecular molecular sizes and intermolecular forces.forces.

Boiling point ElevationBoiling point Elevation Because a non-volatile solute lowers Because a non-volatile solute lowers

the vapor pressure it raises the the vapor pressure it raises the boiling point.boiling point.

The equation is: The equation is: T = KT = Kbbmmsolute solute

T is the change in the boiling pointT is the change in the boiling point KKbb is a constant determined by the is a constant determined by the

solvent.solvent. mmsolute solute is the molality of the soluteis the molality of the solute

Freezing point DepressionFreezing point Depression Because a non-volatile solute lowers the Because a non-volatile solute lowers the

vapor pressure of the solution it lowers vapor pressure of the solution it lowers the freezing point.the freezing point.

The equation is: The equation is: T = KT = Kffmmsolute solute

T is the change in the freezing pointT is the change in the freezing point KKff is a constant determined by the is a constant determined by the

solventsolvent mmsolute solute is the molality of the soluteis the molality of the solute

1 atm

Vapor Pressure of solution

Vapor Pressure of pure water

1 atm

Freezing and boiling points of water

1 atm

Freezing and boiling points of solution

1 atm

TfTb

Electrolytes in solutionElectrolytes in solution Since colligative properties only Since colligative properties only

depend on the number of molecules, depend on the number of molecules, Ionic compounds should have a Ionic compounds should have a bigger effect.bigger effect.

When they dissolve they dissociate.When they dissolve they dissociate. Individual Na and Cl ions fall apart.Individual Na and Cl ions fall apart. 1 mole of NaCl makes 2 moles of ions.1 mole of NaCl makes 2 moles of ions. 1mole Al(NO1mole Al(NO33))33 makes 4 moles ions. makes 4 moles ions.

Electrolytes have a bigger impact on Electrolytes have a bigger impact on omelting and freezing points per omelting and freezing points per mole because they make more mole because they make more pieces.pieces.

TryTry

Automotive antifreeze consists of Automotive antifreeze consists of ethylene glycol Cethylene glycol C22HH66OO22, a non-volatile , a non-volatile nonelectrolyte. Calculate the boiling nonelectrolyte. Calculate the boiling point and freezing point of a 25. point and freezing point of a 25. mass percent solution of ethylene mass percent solution of ethylene glycol in water.glycol in water.

KKbb= .52°C/m= .52°C/m

KKff= 1.86°C/m = 1.86°C/m

Try again!Try again!

List the following solutions in order of List the following solutions in order of their expected freezing points: 0.05 their expected freezing points: 0.05 m CaClm CaCl22, 0.15 m NaCl, 0.10 m HCl, , 0.15 m NaCl, 0.10 m HCl, 0.05 HC0.05 HC22HH33OO22, 0.10 m C, 0.10 m C1212HH2222OO1111

OsmosisOsmosis

Occurs through a semi permeable Occurs through a semi permeable membrane. A membrane that membrane. A membrane that usually allows the migration of small usually allows the migration of small water molecules and not larger water molecules and not larger solute molecules. solute molecules.

The net movement of solvent is The net movement of solvent is always toward the solution with a always toward the solution with a higher solute concentration.higher solute concentration.

Osmotic PressureOsmotic Pressure

The pressure required to prevent The pressure required to prevent osmosis (Fig 13.23). osmosis (Fig 13.23).

Osmotic Pressure (Osmotic Pressure (ππ)) ΠΠ= (n/V) RT=MRT= (n/V) RT=MRT

M=molarityM=molarity R= gas laws constantR= gas laws constant T= temp (K)T= temp (K)

Isotonic- when two solutions of Isotonic- when two solutions of identical osmotic pressure are identical osmotic pressure are separated by a semi-permeable separated by a semi-permeable membrane, no osmosis will occurmembrane, no osmosis will occur

Hypotonic- when one solution has Hypotonic- when one solution has lower osmotic pressure compared to lower osmotic pressure compared to the otherthe other

The more concentrated one would be The more concentrated one would be hypertonichhypertonich

People who eat salty foods retain People who eat salty foods retain waterwater

Cucumbers shrivel up in a salt water Cucumbers shrivel up in a salt water solution to make picklessolution to make pickles

Osmosis is spontaneous.Osmosis is spontaneous.

Active transport-oppositeActive transport-opposite

Try 2!Try 2!

The average osmotic pressure of blood The average osmotic pressure of blood is 7.7 atm at 25°C. What is 7.7 atm at 25°C. What concentration of glucose will be concentration of glucose will be isotonic with blood?isotonic with blood?

What is the osmotic pressure at 20°C What is the osmotic pressure at 20°C of a 0.0020 M sucrose Cof a 0.0020 M sucrose C1212HH2222OO1111 solution?solution?

ColloidsColloids

Somewhere between a solution and a Somewhere between a solution and a heterogeneous mixtureheterogeneous mixture

Does not separate upon standingDoes not separate upon standing Diameter of 10-2000 ADiameter of 10-2000 A Scatter light- Tyndall EffectScatter light- Tyndall Effect When colloids are dispersed in water When colloids are dispersed in water

they can be hydrophyllic or they can be hydrophyllic or hydrophobichydrophobic