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Solutions and their Behavior. Goals: Calculate solution concentration . Describe the solution process . Apply colligative properties of solutions. Describe colloids and their applications. Solutions. A solution is a ______________ mixture of 2 or more substances in a single phase. .

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solutions and their behavior

Solutions and their Behavior

Goals:

Calculate solution concentration.

Describe the solution process.

Apply colligative properties of solutions.

Describe colloids and their applications.

solutions
Solutions

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

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

types of solutions
Types of Solutions

Solute Solvent Solution Example

Gas 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.

equilibrium
Equilibrium

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 equilibrium
Dynamic 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
solutions1
Solutions
  • Solutions can be classified as saturated or _____________.
  • A saturated solution contains the ________ ______________ that dissolves at that temperature.
dynamic equilibrium1
Dynamic 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) nitrate

The 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 __________ ___________________________________________________ __________________________________________________.
solutions2
Solutions
  • Solutions can be classified as unsaturated or saturated.
  • A saturated solution contains the maximum quantity of solute that dissolves at that temperature.
  • ________________ SOLUTIONS contain more than is possible and are unstable.
solutions3
Solutions
  • 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 solid
Dissolving 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 energetics
Dissolving 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 liquids
Liquids 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 compounds
Solubility 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 alcohol

CH3(CH2)2CH2OH Butyl alcohol

CH3(CH2)10CH2OH Lauryl alcohol

CH3CHO Acetaldehyde

C12H22O11 Sucrose

solubility of gases
Solubility 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 henry s law
Factors Affecting Solubility: Henry’s Law
  • The solubility of a gas in a liquid is directly proportional to the gas pressure.

Sg = kHPg

henry s law
Henry’s Law

Gas solubility (mol/L) = kH • Pgas

When Pgas drops, solubility drops.

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

factors affecting solubility le chatelier s principle
Factors Affecting Solubility: Le Chatelier’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 temperature
Solubility and Temperature

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

energetics of the solution process
Energetics of the Solution Process
  • 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 acetate
Supersaturated 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.

NaCH3CO2 (s) ----> Na+(aq) + CH3CO2-(aq)

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

Na+(aq) + CH3CO2-(aq) ---> NaCH3CO2 (s)

+ heat

+ heat

calculate heat of solution d h o soln
Calculate Heat of solution (DHosoln)

DHosoln = DHof products – DHof reactants

colligative properties
Colligative Properties

On adding a solute to a solvent, the props. of the solvent are modified.

  • Vapor pressure decreases
  • Melting point decreases
  • Boiling point increases
  • Osmosis is possible (osmotic pressure)

These changes are called COLLIGATIVE PROPERTIES.

They depend only on the NUMBER of solute particles relative to solvent particles, not on the KIND of solute particles.

concentration units
Concentration Units
  • An IDEAL SOLUTION is one where the properties depend only on the concentration of solute.
  • Need concentration units to tell us the number of solute particles per solvent particle.
  • The unit “molarity” does not do this!
molarity and molality
Molarity 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 units1

mol solute

m of solute

=

kilograms solvent

Concentration Units

MOLALITY, m

MOLE FRACTION, X

For a mixture of A, B, and C

WEIGHT % = grams solute per 100 g solution

ppm = grams solute per 1 million g solution

what is the m of a 29 5 by mass ethanol solution mw ethanol 46g mol
What is the m of a 29.5% by mass ethanol solution (mw ethanol = 46g/mol)?

Student should be familiar with concentration calculations.

colligative properties1
Colligative Properties
  • Depend only on the _______________ ______________ relative to solvent particles, not on the KIND of solute particles
  • When a solute is present, the vapor pressure of the solvent is __________.
liquid vapor equilibrium
Liquid-Vapor Equilibrium
  • To understand colligative properties, study the LIQUID-VAPOR EQUILIBRIUM for a solution.
raoult s law
Raoult’s Law

VP of H2O over a solution depends on the number of H2O molecules per solute molecule.

Psolventproportional to Xsolvent

Psolvent = Xsolvent • Posolvent

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

RAOULT’S LAW

raoult s law1
Raoult’s Law

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

PA = XA • PoA

Because mole fraction of solvent, XA, is always less than 1, then PA is always less than PoA.

The vapor pressure of solvent over a solution is always LOWERED!

boiling point elevation

gas

liquid

Boiling Point Elevation

A 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.

boiling point elevation1
Boiling Point Elevation

Elevation in BP = ∆TBP = KBP•m

(where KBP is characteristic of solvent)

freezing point depression

liquid

solid

Freezing Point Depression

The 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.

freezing point depression1
Freezing Point Depression

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

FP depression = ∆TFP = KFP•m

Ethylene glycol/water

solution

Pure water

freezing point depression2
Freezing Point Depression

Water with and without antifreeze

When a solution freezes, the solid phase is pure water. The solution becomes more concentrated.

applications of d t
Applications of DT
  • Antifreeze
  • Ice cream makers
  • CaCl2 on icy roads in winter
  • Measure molar masses
  • Distinguish between electrolytes and non-electrolytes.
boiling point elevation and freezing point depression
Boiling Point Elevation and Freezing Point Depression

∆T = K•m•i

A generally useful equation

i = van’t Hoff factor = number of particles produced per formula unit.

Compound Theoretical Value of i

glycol 1

NaCl

CaCl2

which solution will have a lower freezing point
Which solution will have a lower 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.

osmosis
Osmosis

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

_________– 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.

osmotic pressure
Osmotic Pressure

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

Solvent molecules move from pure solvent to solution in an attempt to make both have the same concentration of solute.

Driving force is entropy

osmotic pressure1
Osmotic Pressure
  • Osmotic Pressure (p) follows an equation much like the ideal gas law:

p V = nRT

or,p = MRT

R = 0.0806 L atm/molK

M = concentration of particles (moles or ions) in mol/L

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

osmotic pressure2
Osmotic 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 osmosis
Applications 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).

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

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

Normal cell

applications of osmosis2
Applications of Osmosis
  • Reverse Osmosis

Water desalination plant in Tampa

dyalisis
Dyalisis
  • 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.
  • 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).
colloids
Colloids
  • 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).
colloids1
Colloids
  • 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.
colloids2
Colloids
  • 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.

colloids3
Colloids
  • 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.
colloids4
Colloids
  • 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.
colloids5
Colloids

 Phospholipid and vesicle

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.

 Surfactant (soap molecule) and micelles

remember
Remember
  • 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.