Solutions and Solutions and their Behaviortheir Behavior

Goals:

1. Calculate solution concentration.2.Describe the solution process.3.Apply colligative properties of solutions.4.Describe colloids and their applications.

SolutionsSolutions

A solution is a A solution is a ______________ ______________ mixture of 2 or more mixture of 2 or more substances in a single substances in a single phase. phase.

One constituent is usually One constituent is usually regarded as the regarded as the SOLVENT SOLVENT and the others as and the others as SOLUTESSOLUTES..

Types of SolutionsTypes of SolutionsSolute Solvent Solution ExampleGas Gas Gas Air (O2 in N2)____ _____ _____ Club soda (CO2 in H2O)Liquid Liquid Liquid Wine (alcohol in H2O)____ _____ _____ Saline sol. (NaCl in H2O)____ _____ _____ 14-karat gold (Ag in Au)

Aqueous solutions – those in which __________is the solvent.

EquilibriumEquilibrium

Equilibrium – the ______ of the forward and reverse reactions are _______.

Is __________ – reactants are changing to products, products to reactants; but at the same rate, there is no change in concentration of reactants or products.

Dynamic EquilibriumDynamic Equilibrium

• Dynamic equilibrium – when the number of particles (ions or molecules) leaving the surface of the crystals is equal to the number that is returning.– The net quantity of particles in solution and that in undissolved crystals

remain constant.• Saturated solution – a solution that contains all the solute that it can at

equilibrium and at a given temperature.– 36 g NaCl per 100 g of H2O

• Unsaturated solution – contains less than this quantity.– Any other with less: ex. 20 g NaCl per 100 g of H2O

SolutionsSolutions• Solutions can be

classified as saturated or _____________.

• A saturated solution contains the ________ ______________ that dissolves at that temperature.

Dynamic EquilibriumDynamic Equilibrium• Precipitate – an insoluble or nearly insoluble solid that separates

from a solution.– When a saturated solution is cooled, solute precipitates until the

equilibrium is once again established at the lower temperature.

60oC 100 g water dissolve 95 g of lead (II) nitrate: Pb(NO3)2

5oC 100 g water dissolve 40 g of lead (II) nitrateThe excess 55 g will separate as precipitate upon cooling, increasing the quantity of undissolved solute.

• Supersaturated solution – a solution containing solute in excess of what it could contain if it were at __________.– It is not a stable system because it is not _______________.– Solute may precipitate when the solution is stirred or the inside of

the container is scratched with a glass rod.– Addition of a “seed” crystal will nearly always result in

__________ ___________________________________________________ __________________________________________________.

SolutionsSolutions• Solutions can be classified Solutions can be classified

as unsaturated or saturated.as unsaturated or saturated.• A saturated solution A saturated solution

contains the maximum contains the maximum quantity of solute that quantity of solute that dissolves at that dissolves at that temperature.temperature.

• ________________ ________________ SOLUTIONSSOLUTIONS contain more contain more than is possible and are than is possible and are unstable.unstable.

SolutionsSolutions• The solubility of a given solute depends on the

relative __________________particles in the pure substances and in the solution.

• Three things must happen:– The attractive forces holding the ions of the solute

together must be overcome.– The attractive forces holding at least some of the solvent

molecules must be overcome.– The solute and solvent molecules must interact; they must

attract one another.

• _____________ – process in which water molecules surround the solute ions.

Dissolving an Ionic SolidDissolving an Ionic Solid

• The polarity of water molecules enables them to attract (and be attracted by) ions. Several ion-dipole interactions surround each ion and overcome the stronger ion-ion interactions.

Dissolving an Ionic Solid: EnergeticsDissolving an Ionic Solid: Energetics

• Almost all compounds of the Group 1A elements are soluble in water: NaCl, Na2SO4, K3PO4, LiBr

• Many solids in which both ions are doubly or triply charged are essentially insoluble in water (forces holding the ions together are so strong that they cannot be overcome by the hydration of the ions): CaCO3, AlPO4, BaSO4.

Which ion is most strongly hydrated?Which ion is most strongly hydrated?

• Na+

• Mg2+

• Cs+

Energy of hydration depends on the ________ of the ion and the _______ between the ion and the dipole.

Liquids dissolving LiquidsLiquids dissolving Liquids

• ___________– substances that can be mixed in all proportions (water and alcohol).

• __________– the quantity that will dissolve is near zero (iron in water).

• ___________– an appreciable quantity dissolves (sugar in water).

Solubility of Covalent CompoundsSolubility of Covalent Compounds

• Like dissolves like. Nonpolar (or slightly polar) solutes dissolve best in nonpolar solvents; polar solutes dissolve best in polar solvents.

• Water solubility of covalent compounds depends mainly on the ability of water to form _____________ to the solute molecules. Molecules containing a high proportion of nitrogen or oxygen atoms will dissolve in water.

Which of the following will dissolve in water?Which of the following will dissolve in water?

CH3OH Methyl alcoholCH3(CH2)2CH2OH Butyl alcoholCH3(CH2)10CH2OH Lauryl alcoholCH3CHO AcetaldehydeC12H22O11 Sucrose

Solubility of GasesSolubility of Gases Carbonated beverages (CO2 in water) Formalin (HCHO (formaldehyde gas)) Ammonia (NH3 in water)

• Unlike most solids, gases become less soluble in water as the temperature _____________. The gas molecules acquire more kinetic energy and escape the solution.

• At constant T, the solubility of a gas in water is directly proportional to the __________ of the gas in equilibrium with the aqueous solution. The higher the _______, the more gas will dissolve in a given volume of water.

– The pressure inside soda bottles is high enough to dissolve the wanted CO2, once the bottle is opened, the pressure is released and the gas escapes.

Factors Affecting Solubility: Factors Affecting Solubility: Henry’s LawHenry’s Law

• The solubility of a gas in a liquid is directly proportional to the gas pressure.

Sg = kHPg

Henry’s LawHenry’s Law

Gas solubility (mol/L) = kGas solubility (mol/L) = kHH • P • Pgasgas

When When PPgasgas drops, solubility drops. drops, solubility drops.

Think about: When would Henry’s Law not apply?Think about: When would Henry’s Law not apply?

Factors Affecting Solubility: Le Factors Affecting Solubility: Le Chatelier’s PrincipleChatelier’s Principle

• A change in any of the factors determining an equilibrium causes the system to adjust so as to reduce or counteract the effect of the change. Henri Louis Le Chatelier (1884).

– change in T, P, concentration of reactants or products.

• Temperature affects solubility.• For all gases in water, solubility decreases

with temperature.

Solubility and TemperatureSolubility and Temperature

Simple correlations of solubility with structure or thermodynamic parameters are generally not successful.

Energetics of the Solution Energetics of the Solution ProcessProcess

• If the enthalpy of formation of the solution is more negative that that of the solvent and solute, the enthalpy of solution is negative.

• The solution process is exothermic!

Supersaturated Sodium AcetateSupersaturated Sodium Acetate

• One application of a supersaturated solution is the sodium acetate “heat pack.”

• Sodium acetate has an ENDOthermic heat of solution.

Sodium acetate has an ENDOthermic heat of solution. Sodium acetate has an ENDOthermic heat of solution. NaCHNaCH33COCO22 (s) (s) ----> Na ----> Na++(aq) + CH(aq) + CH33COCO22

--(aq)(aq)

Therefore, formation of solid sodium acetate from its Therefore, formation of solid sodium acetate from its ions is EXOTHERMIC.ions is EXOTHERMIC.

NaNa++(aq) + CH(aq) + CH33COCO22--(aq) ---> NaCH(aq) ---> NaCH33COCO22 (s) (s)

+ heat

+ heat

Calculate Heat of solution (Calculate Heat of solution (∆∆HHoosolnsoln))

∆Hosoln = Σ ∆Ho

f products – Σ ∆Hof reactants

Colligative PropertiesColligative PropertiesOn adding a solute to a solvent, the props. of On adding a solute to a solvent, the props. of

the solvent are modified.the solvent are modified.• Vapor pressure Vapor pressure decreasesdecreases• Melting point Melting point decreasesdecreases• Boiling point Boiling point increasesincreases• Osmosis is possible (osmotic pressure)Osmosis is possible (osmotic pressure)These changes are called COLLIGATIVE These changes are called COLLIGATIVE

PROPERTIES. PROPERTIES. They depend only on the NUMBER of solute They depend only on the NUMBER of solute

particles relative to solvent particles, not on particles relative to solvent particles, not on the KIND of solute particles.the KIND of solute particles.

Concentration UnitsConcentration Units

• An An IDEAL SOLUTIONIDEAL SOLUTION is one where is one where the properties depend only on the the properties depend only on the concentration of solute.concentration of solute.

• Need concentration units to tell us the Need concentration units to tell us the number of solute particles per solvent number of solute particles per solvent particle.particle.

• The unit “molarity” does not do this!The unit “molarity” does not do this!

Molarity and MolalityMolarity and Molality• Molarity: Moles of solute

per liter of solution.M = moles/L

• Molality: Moles of solute per kilogram of solvent.

m = moles/Kg

Molality is Temperature _______________!

Concentration UnitsConcentration Units

MOLE FRACTION, XFor a mixture of A, B, and C

XA = mol fraction A = mol A

mol A + mol B + mol C

WEIGHT % = grams solute per 100 g solution

ppm = grams solute per 1 million g solution

MOLALITY, mm of solute =

mol solutekilograms solvent

What is the What is the mm of a 29.5% by mass ethanol of a 29.5% by mass ethanol solution (mw ethanol = 46g/mol)?solution (mw ethanol = 46g/mol)?

Student should be familiar with concentration calculations.

Colligative PropertiesColligative Properties• Depend only on the _______________ Depend only on the _______________

______________ relative to solvent ______________ relative to solvent particles, not on the KIND of solute particles, not on the KIND of solute particlesparticles

• When a solute is present, the vapor When a solute is present, the vapor pressure of the solvent is __________.pressure of the solvent is __________.

Liquid-Vapor EquilibriumLiquid-Vapor Equilibrium• To To

understand understand colligative colligative properties, properties, study the study the LIQUID-LIQUID-VAPOR VAPOR EQUILIBRIUEQUILIBRIUMM for a for a solution.solution.

Raoult’s LawRaoult’s Law

PPsolventsolvent = X = Xsolventsolvent • P • Poosolventsolvent

PPsolventsolvent = X = Xsolventsolvent • P • Poosolventsolvent

VP of HVP of H22O over a solution depends on the O over a solution depends on the number of Hnumber of H22O molecules per solute O molecules per solute molecule.molecule.

PPsolventsolvent proportional toproportional to X Xsolventsolvent

Vapor Pressure of solvent over solution Vapor Pressure of solvent over solution = (Mol frac solvent)•(VP pure solvent)= (Mol frac solvent)•(VP pure solvent)

RAOULT’S LAWRAOULT’S LAW

Raoult’s LawRaoult’s Law

PPAA = X = XAA • P • PooAAPPAA = X = XAA • P • PooAA

An An _______ solution_______ solution is one that is one that obeys Raoult’s law.obeys Raoult’s law.

Because mole fraction of solvent, XBecause mole fraction of solvent, XAA, is always , is always

less than 1, then Pless than 1, then PAA is always less than P is always less than PooAA..

The vapor pressure of solvent over a solution The vapor pressure of solvent over a solution

is always is always LOWEREDLOWERED!!

Changes in Boiling Points of Changes in Boiling Points of SolventSolvent

See Figure 14.14See Figure 14.14

VP solventafter addingsolute

VP Pure solvent

BP puresolvent

BP solution

1 atm

P

T

Boiling Point ElevationBoiling Point ElevationA nonvolatile solute particle (purple) can block the escape of the solvent particles (blue) but has no effect on the return of the solvent particles from the vapor to the solution.

gas

liquid

Boiling Point ElevationBoiling Point Elevation

Elevation in BP = ∆TBP = KBP•mElevation in BP = ∆TBP = KBP•m(where KBP is characteristic of solvent)(where KBP is characteristic of solvent)

Freezing Point DepressionFreezing Point DepressionThe rate at which solvent molecules (blue) leave the pure solid solvent is unaffected by the presence of solute particles (purple) nearby in the solution, but their rate of return to the solid is reduced.

liquid

solid

Freezing Point DepressionFreezing Point Depression

The freezing point of a solution is The freezing point of a solution is ________ ________ than that of the pure solvent.than that of the pure solvent.

FP depression = ∆TFP depression = ∆TFPFP = K = KFPFP•m•m

Pure waterPure water Ethylene glycol/water Ethylene glycol/water solutionsolution

Freezing Point DepressionFreezing Point Depression

Water with and without antifreeze When a solution freezes, the solid phase is pure water. The solution becomes more concentrated.

Applications of Applications of ∆∆TT• Antifreeze• Ice cream makers• CaCl2 on icy roads in

winter• Measure molar masses• Distinguish between

electrolytes and non-electrolytes.

Boiling Point Elevation and Boiling Point Elevation and Freezing Point DepressionFreezing Point Depression

∆∆T = K•m•iT = K•m•iA generally useful equation A generally useful equation i = van’t Hoff factor = number of particles i = van’t Hoff factor = number of particles

produced per formula unit.produced per formula unit.CompoundCompound Theoretical Value of iTheoretical Value of iglycolglycol 11NaClNaClCaClCaCl22

How much NaCl must be dissolved in 4.00 kg of How much NaCl must be dissolved in 4.00 kg of water to lower the Freezing Point to -10.00 water to lower the Freezing Point to -10.00 ooC?C?

Which solution will have a lower Which solution will have a lower freezing point?freezing point?

• 0.1 m glucose

• 0.06 m NaCl

• 0.06 m Na2SO4

Student should be familiar with predicting freezing and boiling point of solutions.

OsmosisOsmosis

_________– net diffusion of water through a semipermeable membrane. Net flow of solvent from the more dilute solution (or pure solvent) into the more concentrated solution.

Semipermeable membrane: solvent molecules can pass, but flow of solute is restricted.

Osmotic PressureOsmotic PressureEquilibrium is reached when Equilibrium is reached when pressure — the pressure — the OSMOTIC PRESSURE, OSMOTIC PRESSURE, ∏∏ — produced by extra — produced by extra solution counterbalances solution counterbalances pressure of solvent pressure of solvent molecules moving thru the molecules moving thru the membrane.membrane.

Solvent molecules move from Solvent molecules move from pure solvent to solution in an pure solvent to solution in an

attempt to make both have the attempt to make both have the same concentration of solute.same concentration of solute.

Driving force Driving force is entropyis entropy

Osmotic PressureOsmotic Pressure• Osmotic Pressure (ππ) follows an equation much

like the ideal gas law: π π V = nRT

or, ππ = MRTR = 0.0806 L atm/molKM = concentration of particles (moles or ions) in mol/L

Useful for determining molar masses of large molecules like proteins and polymers.

Osmotic PressureOsmotic Pressure

– Examples of osmosis are found in living organisms: Cells are semipermeable; their function and survival depend on maintenance of the same osmotic pressure inside the cell and outside in the extracellular fluid.

– Isotonic solution – Iso-osmotic – a solution having the same osmotic pressure as body fluids (0.89% NaCl (mass/vol)).

Applications of OsmosisApplications of Osmosis– ___________ solution – a solution having higher osmotic pressure

than body fluids (larger than 0.89% NaCl).– ___________ solution – a solution having lower osmotic pressure

than body fluids (less than 0.89% NaCl).

Normal cell Water flows out of the cell and cell wrinkles (crenation).

Water flows into the cell and cell is swollen and may burst (plasmolysis).

Applications of OsmosisApplications of Osmosis

Applications of OsmosisApplications of Osmosis• Reverse Osmosis

Water desalination plant in Tampa

DyalisisDyalisis

• Dialysis – process in which small molecules and ions pass through a dialyzing membrane. In osmosis, osmotic membranes pass only solvent molecules.– Bags of cellophane or collodion. – Kidneys are a complex dialyzing system responsible for the removal of

waste products from the blood.• Creatinine concentration > 900 mmol/L indication to start dialysis (kidney

failure).

• Dialyzing membranes – membranes that pass small molecules and ions while holding back large molecules and colloidal particles.

• Ions and small molecules always diffuse from higher concentration to lower concentration.

ColloidsColloids• Suspension – two substances momentarily mixed, but

solute will settle to the bottom of the container. It can be separated by ___________ . It is a _______________ mixture (sand and water).

• Colloids – halfway point (particles of 1 nm-1000 nm) between true solutions (particles less than 1 nm) and suspensions (particles of 1000 nm or more).

ColloidsColloids• Left: Fine sand (silica) added to

water will quickly settle, producing a heterogeneous mixture with water on top and silica on the bottom.

• Right: The same proportion of silica, specially prepared (Ludox), produces a colloidal dispersion. The particles of hydrated silica, SiO2*xH2O, are much larger than atoms and ordinary molecules. However, the sodium hydroxide used in preparing the dispersion causes the silica particles to acquire a negative charge from adsorbed hydroxide ions. The similarly charged silica particles repel one another and stay suspended indefinitely.

ColloidsColloids

• Colloids – halfway point between true solutions and suspensions.– Appear milky or cloudy; some may appear clear.– Tyndall effect – John Tyndall, 1968 – scattering of a beam

of light.

The light beam is not visible as it passes through a true solution (left), but it is readily visible as it passes through colloidal iron (III) oxide in water.

ColloidsColloids– Particles in a colloid are often charged, due to the

adsorption of ions on the surface of the particle. Because like charges repel, particles tend to stay away from one another (they do not form particles large enough to settle out).

– May separate by adding highly charged ions (it will coalesce).

– Are stabilized by addition of a protective coating material – soap added to emulsify oil in water. Milk is an emulsion of fat droplets stabilized by casein, a protein molecule.• Emulsifying agents – stabilize

emulsions.

ColloidsColloids• Cationic emulsion technology – for the absorption of

substances that are not soluble in water and large molecules. The technology can be used for injectables, eye drops (ophthalmology), creams/lotions (dermatology) and capsules (oral administration).

• Cationic agent is used because the cell wall has negative charges.

ColloidsColloids

 Surfactant (soap molecule) and micelles

The ionic portion of the surfactant is more stable when solubilized by water, whereas the nonpolar portion of the surfactant is more stable when surrounded by other nonpolar chains. They might form micelles.

Phospholipids spontaneously form vesicles in water, encapsulating a small water droplet in a spherical shell of phospholipid molecules. Both the inner and outer wall of the shell are composed of hydrophilic heads, whereas the inside of the vesicle shell is the alkane tails. The image below is a slice through a spherical vesicle.

 Phospholipid and vesicle

Types of ColloidsTypes of Colloids

RememberRemember• Go over all the contents of your

textbook.• Practice with examples and with

problems at the end of the chapter.• Practice with OWL tutor.• Work on your assignment for Chapter 14.