Lecture outline: Chapter 13 Review of solution terms P ti

Lecture outline: Chapter 13P ti f l tiProperties of solutions

Wh l i f h l l l l•Why solutions form at the molecular level

•Units of solution concentration

•Colligative properties: effects of solutes on BP, MP, and vapor pressure, , a d apo p essu e

•Osmotic pressure

1S. Ensign, solutions

Review of solution terms• Solution: a homogeneous mixture of 2 or more

substances• Solvent: the component of the solution present in

greatest quantity• Solute: a substance dissolved in the solvent• Solubility: a term that refers to how much of a

solute can dissolve in a given solvent (grams solute dissolved/100 ml solution)Mi ibl t b t th t f l ti• Miscible: two substances that can form a solution at all solute-solvent proportions


The solution process• “soluble” in water: glucose, NaCl, NaOH,

acetic acid, MgSO4 (“soluble” means aacetic acid, MgSO4 ( soluble means a significant amount can dissolve)

• “Insoluble” in water: CaCO AgCl C H I• Insoluble in water: CaCO3, AgCl, C6H14, I2(“insoluble” means a very little amount dissolves)dissolves)

• “miscible” with water: ethanol, glycerol, formaldehyde (“miscible” means soluble at allformaldehyde (“miscible” means soluble at all proportions)


The solution processp• Why do some substances dissolve in water

while others don’t? Consider strengths of:while others don t? Consider strengths of:1. Solvent-solvent intermolecular forces (BREAK)2 Solute solute intermolecular forces (BREAK)2. Solute-solute intermolecular forces (BREAK)3. Solvent-solute intermolecular forces (solvation,

hydration) (FORM)hydration) (FORM)

Remember, it takes energy to break a bond or intermolecular attraction, while the formation of a new bond or intermolecular attraction releases energy


Solvent (e.g. water)

5Solute (e.g. glucose)

S. Ensign, solutions

Sodium chloride dissolves in water to form hydrated sodium and choride ionsy

+

-


Hydrated chloride and sodium ions: ion-di l tt tidipole attractions

Na+Cl-


The dissolving process can be exothermic, endothermic, or “isothermic”,

• NaCl in water: ΔT ~ 0

• NaOH in water: ΔT > 0

• (NH )(CH COO) in water: ΔT < 0• (NH4)(CH3COO) in water: ΔT < 0


Another term important in dictatingAnother term important in dictating whether a reaction occurs

“Entropy”

Thermodynamics chemistry 2: chemical reactionsThermodynamics, chemistry 2: chemical reactions that occur with an increase in the “disorder” (randomness) of the system are favored(randomness) of the system are favored


Dynamic equilibrium: when two opposing processes occur at the same rate, so that there is no net change in the state of the system

Example 1: vapor pressure inExample 1: vapor pressure in a sealed container of water

rateescape = ratereturn

Example 2: a saturated psolution containing undissolved solute

10

ratesolute dissolving = ratesolute crystallizing


Factors affecting solubilityg y

•Nature of solute-solvent interactions•Nature of solute-solvent interactions

•Pressure

•Temperature




•Pressure

•Temperature

“like dissolves like”polar + polarpolar + polarnonpolar + nonpolar

12

p pS. Ensign, solutions

What molecules dissolve in water? • soluble salts (ion-dipole interactions)

• polar moleculesH b di– H-bonding

– polar but no H-bonding


Some polar molecules in water


Solubility of alcohols in waterH

C O HH

H

C O H

H

C

H

H C O HC

HH

H

C O H

H

C

H

C

H

H

HHH

HHHH

15C O HC

HH

CC

H

H

H S. Ensign, solutions

Small compounds with hydroxyl groups tend to dissolve in water Htend to dissolve in water• Glycerol (nontoxic) C O HH

C OH H

C

H

OH H

• Propylene glycol (nontoxic)C O H

H

H

C

C

H

OH

HH

H

• Ethylene glycol (highly toxic) H

C O H

H

H

16

C OH H

HS. Ensign, solutions

Glucose, C6H12O6

C

OH H

C

C OHOC

C

H

H

O

HH

C HO

C OHC

COO

OHHC

CH

H

H

H

C OH

C

H OH HH

H O HCH

H

O H


nonpolar + nonpolar


nonpolar + nonpolar

Cl H H H H H

CCl

ClCl

H C C

H H

C

H

C

H

C

H

H


Mix solutions of CCl4 and H2O together:density, H2O ~ 1 g/ml

density, CCl4 ~ 1.6 g/mldensity, CCl4 1.6 g/ml


Mix solutions of CCl and H OCCl4 and H2O together:

density, H2O ~ 1 g/ml

CC /density, CCl4 ~ 1.6 g/ml


Mix solutions of CCl4 and H2O together:

density, H2O ~ 1 g/ml

density CCl ~ 1 6 g/mldensity, CCl4 ~ 1.6 g/ml


If you added CuSO4 to the separatory funnel, thenseparatory funnel, then shook it, where would the CuSO end up?CuSO4 end up?


If you added I2 to the separatory funnel, thenseparatory funnel, then shook it, where would the I2end up?end up?


Gases in water

• N2

• CO• O2

• ArK• Kr


Solubility data for some gases in water at 298 K

Molecule Mr structure Predominant intermolecular attraction with water

Solubility (g solute/kg H2O)

H2 2.02 H H London 0.0015

CH4 16.1 C

H

London 0.021CH4 16.1 CH

HH

London 0.021

N2 28 N N London 0.018

O2 32 O O London 0.039

CO2 44 C OO London 1.5

H2S SH

H

Dipole-dipole 3.3

SO2

OS

O

Dipole-dipole and hydrogen bonding 94

S. Ensign, solutions26

NH3 NH

HH

Hydrogen bonding 470



•PressureHenry’s law constant for the gas sol ent pair

•Temperature

F C kP

gas-solvent pair at a defined temperature

For gases: Cg = kPg

Partial pressure of gas over

Solubility of gas in solution phase

27

solution


Dynamic equilibrium: when two i t thopposing processes occur at the

same rate, so that there is no net h i th t t f th tchange in the state of the system

•Example 1: vapor pressure in p p pa sealed container of water

E l 2 t t d•Example 2: a saturated solution containing ndissol ed sol teundissolved solute

•Example 3: the solubility of a

28

p ygas in water


Air: ~78% N2, 21% O2 by volume

Rateescape = rate return,O2 ,O2

Rateescape = rate return,N2 ,N2

S. Ensign, solutions29

What is the concentration of dissolved oxygen in a fresh-water stream in equilibrium with air at 25°C and 1 atm. P?k 1 66 10 6 M/ HkO2

= 1.66 x 10-6 M/mm HgXO2

= 0.21Cg = kPg

P1 = X1PT


Examples of Henry’s law• Bottle of soda pop

• Scuba diving


Examples of Henry’s law• Scuba diving




•Pressure

•Temperature


In general, but not always, the solubility of solid solutes increases with increasing temperature

The solubility of gases decreases with increasing temperature


Units of solution concentration• Molarity molsolutemols• Molarity

• Molality

M==l

molsolution literssolute mols

l tl• Molality

M l f ti

m=solvent kg

solute mols

• Mol fraction

M %• Mass %

• Volume %

35

• Parts per millionS. Ensign, solutions

The density of water changes as a f ti f t tfunction of temperature

Density of water at different temperatures

1.000

1.001

ty (g

/ml)

0.998

0.999

dens

it

0.997

0 5 10 15 20 25 30 350.995

0.996

36

temperature (°C)

0 5 10 15 20 25 30 35



Solution prepared at 25° C….Density of water at different temperatures

1.000

1.001

(g/m

l)

0 998

0.999

dens

ity

0.997

0.998 1.00 l

0 5 10 15 20 25 30 350.995

0.996

temperature (°C)

0 5 10 15 20 25 30 35



Solution cooled to 25° C….Density of water at different temperatures

1.000

1.001

(g/m

l)

0 998

0.999

dens

ity

0.997

0.998 1.00 l

0 5 10 15 20 25 30 350.995

0.996

temperature (°C)

0 5 10 15 20 25 30 35


Units of solution concentration• Molarity molsolutemols• Molarity

• Molality

M==l

molsolution literssolute mols

l tl• Molality

M l f ti

m=solvent kg

solute mols

• Mol fraction

M %t

11 n

nx =

Af• Mass % 100 x mass total

Aof massA % mass =

• Volume % v/v; m/v

39

• Parts per million 610 x mass total

A of massA ppm =S. Ensign, solutions

Units of solution concentration (cont.)• Parts per million• Parts per million

610A of massAppm x= 10 mass total

A ppm x=

⎞⎛ 610 totalg

A g x⎟⎟⎠

⎞⎜⎜⎝

⎛

⎠⎝

⎟⎞

⎜⎛

⎟⎞

⎜⎛

⎟⎞

⎜⎛ g 1000mg 1000A g

⎟⎟⎠

⎜⎜⎝

⎟⎟⎠

⎜⎜⎝

⎟⎟⎠

⎜⎜⎝ kg 1

g 1g

g totalgg xx


Units of solution concentration (cont.)• When the units of a solution are expressed in units of• When the units of a solution are expressed in units of

“mg/kg”, they are already expressed in units of ppm, so you don’t have to multiply by 106 anymore!y p y y y

610 totalg

A gA ppm x=solutionkg

A mg A ppm = totalg solutionkg


Units of solution concentration (cont.)• In dilute aqueous solutions• In dilute aqueous solutions,

density, H2O ~ 1g/ml = 1 kg/l

solutionmlA g

solutionliterA mg

solutionkgA mg A ppm μ

===solution mlsolutionliter solution kg


What is the mass % (w/w) composition of a solution prepared by mixing 46 1of a solution prepared by mixing 46.1 grams ethanol with 162 grams water??

100 x mass total

A of massA % mass =


What is the volume % (v/v) composition of a solution prepared by mixing 46.1 grams ethanol p p y g gwith 162 grams water?? dH2O = 1.0 g/ml

d = 0 79 g/mldethanol = 0.79 g/ml


Sodium hydrogen sulfite, NaHSO3, is used to adjust the pH of swimming pools. What is the concentration of Na+ ion in ppm in a 110,000 gallon (4.5 x 105 liter) swimming pool to which 560 grams NaHSO3 was added?

solution mlA g

solutionliter A mg

solution kgA mg A ppm μ

===


Colligative properties: the effects of solute concentration on the properties of a solution•Vapor pressure lowering

•Boiling point elevation (raising)•Boiling point elevation (raising)

•Freezing point depression (lowering)

•Osmosis and osmotic pressure


Vapor pressure lowering

Add solute


47Equilibrium in pure water Equilibrium

reestablishedratecapture > rateescape

The extent of vapor pressure lowering is proportional to the concentration of solute particlesthe concentration of solute particles


Vapor pressure loweringMol fraction of solvent

Raoult’s law: PA = XAP°ARaoult s law: PA XAP A

VaporVapor pressure of pure solvent

Vapor pressure of solution


What is the vapor pressure at 25°C above a solution that contains 46 grams of sucrose in 355 ml of water? The vapor pressure of pure water at 25°C is 23 8 torrThe vapor pressure of pure water at 25 C is 23.8 torr.

Raoult’s law: PA = XAP°A







Boiling point elevation (raising)

Molal conc. of solute

ΔTb = Kbm

of solute particles

ΔTb KbmMolal-boiling pointChange in boiling

52

point elevation constant

point from pure solvent


Boiling point elevation

For H2O, Kb = 0.52° C/m

Molal conc.

ΔT = K m

of solute particles

ΔTb = KbmMolal-boiling

Ch i b ilig


Change in boiling point from pure solvent







Freezing point depression (lowering): molecular explanationp


Equilibrium between ice and liquid water at 0 °C


Ratemelting = ratefreezing

Addition of a solute to ice and liquid water at 0 °C


Ratemelting > ratefreezing

The ice dissolves if temperature stays 0 °C


Ratemelting > ratefreezing

Lowering the temperature below 0 °C slows rate of melting allowing equilibrium to be reestablishedg g q

Melting is endothermic,freezing is exothermicfreezing is exothermic

Δ

solidliquid

Δoutfreezing

solidliquid

Δinmelting

59S. Ensign, solutionsRatemelting = ratefreezing

Freezing point depression (lowering)

For H2O, Kf = 1.86° C/m

Molal conc. of solute

ΔTf = Kfm

of solute particles

ΔTf KfmMolal-boiling pointChange in

60


freezing point from pure solvent







Osmosis: The net movement of solvent across a semi-permeable membrane from the side with lower solute concentration to the side with higher solute concentration

The key to osmosis isThe key to osmosis is the semi-permeable membrane:

62S. Ensign, solutionswater solute

Separation of water on the sides of two glass tubes by the semi-permeable membraney p

S. Ensign, solutions63water solute

Water levels are equal on both sides

Addition of solute molecules to the left side slows rate of water movement from left to right, but not g ,

right to left


Water levels become uequal

Equilibrium is established when sufficient pressure on the left side causes water to move p

between sides at the same rate

ΔhΔh


Water levels at equilibrium dicated by osmotic pressure

Osmotic pressure: The pressure that must be applied on the side with higher solute pp g

concentration in order to prevent net movement of solvent molecules


The membranes of cells are semipermeable membranessemipermeable membranes


Figure Credit: LadyofHats, (Mariana Ruiz Villarreal )http://commons.wikimedia.org/wiki/File:Osmotic_pressure_on_blood_cells_diagram.svg

Some more solution terms•HydrophilicHydrophilic

•Hydrophobic

•Amphipathic

S /d t t•Soap/detergent

•MicelleMicelle

•Colloidal suspension

•macromolecule


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Lecture outline: Chapter 13 Review of solution terms P ti