Physical Properties of SolutionsChapter 13

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용액의 물리적 성질

• 13.1 용액의 유형• 13.2 용해과정의 분자적 고찰• 13.3 농도 단위• 13.4 용해도에 미치는 온도의 영향• 13.5 기체의 용해도에 미치는 압력의 영향• 13.6 총괄성

A solution is a homogenous mixture. 균일 혼합물

The solute is(are) the substance(s) present in the smaller amount(s)

The solvent is the substance present in the larger amount

A saturated solution contains the maximum amount of a solute that will dissolve in a given solvent at a specific temperature.

An unsaturated solution contains less solute than the solvent has the capacity to dissolve at a specific temperature.

A supersaturated solution contains more solute than is present in a saturated solution at a specific temperature.

Sodium acetate crystals rapidly form when a seed crystal isadded to a supersaturated solution of sodium acetate.

Three types of interactions in the solution process:• solvent-solvent interaction• solute-solute interaction• solvent-solute interaction

Hsoln = H1 + H2 + H3

“like dissolves like”

Two substances with similar intermolecular forces are likely to be soluble in each other.

• non-polar molecules are soluble in non-polar solvents

CCl4 in C6H6

• polar molecules are soluble in polar solvents

C2H5OH in H2O

• ionic compounds are more soluble in polar solvents

NaCl in H2O or NH3 (l)

용액 - 균일 혼합물 조성비 - 농도

물리적 표현법• 질량 백분율

화학적 표현법 ( 단위당 화학량 (number))

• 몰농도 (M) mol/Lsolution

• 몰랄농도 (m) mol/kgsolvent

• 몰분율 (x) mol/moltotal

Concentration UnitsThe concentration of a solution is the amount of solute present in a given quantity of solvent or solution.

Percent by Mass

% by mass = x 100%mass of solutemass of solute + mass of solvent

= x 100%mass of solutemass of solution

Mole Fraction (X)

XA = moles of A

sum of moles of all components

Concentration Units Continued

M =moles of solute

liters of solution

Molarity (M)

Molality (m)

m =moles of solute

mass of solvent (kg)

What is the molality of a 5.86 M ethanol (C2H5OH) solution whose density is 0.927 g/mL?

m =moles of solute

mass of solvent (kg)M =

moles of solute

liters of solution

Assume 1 L of solution:5.86 moles ethanol = 270 g ethanol927 g of solution (1000 mL x 0.927 g/mL)

mass of solvent = mass of solution – mass of solute

= 927 g – 270 g = 657 g = 0.657 kg

m =moles of solute

mass of solvent (kg)=

5.86 moles C2H5OH

0.657 kg solvent= 8.92 m

Temperature and Solubility

Solid solubility and temperature

solubility increases with increasing temperature

solubility decreases with increasing temperature

Fractional crystallization is the separation of a mixture of substances into pure components on the basis of their differing solubilities.

Suppose you have 90 g KNO3 contaminated with 10 g NaCl.

Fractional crystallization:

1. Dissolve sample in 100 mL of water at 600C

2. Cool solution to 00C

3. All NaCl will stay in solution (s = 34.2g/100g)

4. 78 g of PURE KNO3 will precipitate (s = 12 g/100g). 90 g – 12 g = 78 g

Temperature and Solubility

Gas solubility and temperature

solubility usually decreases with

increasing temperature

Pressure and Solubility of Gases

The solubility of a gas in a liquid is proportional to the pressure of the gas over the solution (Henry’s law).

c = kP

c is the concentration (M) of the dissolved gas

P is the pressure of the gas over the solution

k is a constant (mol/L•atm) that depends onlyon temperature

low P

low c

high P

high c

Chemistry In Action: The Killer Lake

Lake Nyos, Cameroon, West Africa

Trigger?

• earthquake

• landslide

• strong Winds

1986 Aug. 21CO2 Cloud Released

1700 Casualties

Lake Nyos Degassing Schedule

Composition (1992) :• Layer 40 - 170 m :

– Water : 105 Mm3 – Gas: 190 Mm3

• Layer 170 - 208 m : – Water: 17.5 Mm3 – Gas: 80 Mm3 (1992)

5 pipes at 205 m, internal diameter = 139.8 mm;Liquid flow rate ˜ 2 Mm3/year/pipe

Conclusion: after 3 to 5 years, the situation will be safe.

Figure © Magma Production

총괄성

Colligative properties are properties that depend only on the number of solute particles in solution and not on the nature of the solute particles.

• number of solute particles

• [MA], mA, XA

• PB, mp, bp, .

Colligative Properties of Nonelectrolyte Solutions

Colligative properties are properties that depend only on the number of solute particles in solution and not on the nature of the solute particles.

Vapor-Pressure Lowering

Raoult’s law

If the solution contains only one solute:

X1 = 1 – X2

P 10 - P1 = P = X2 P 1

0 X2 = mole fraction of the solute

P 10 = vapor pressure of pure solvent

X1 = mole fraction of the solvent

P1 = X1 P 10

PA = XA P A0

PB = XB P B0

PT = PA + PB

Ideal Solution

PT = XA P A0 + XB P B

0

= XA P A0 + (1-XA )P B

0

=PB0 + XA (PA

0 – PB0)

Compisition at Vapor Phase

00

0

0

0

0

0

000

0

)1(

)1(

)(

/

A

B

A

A

AA

B

A

B

A

ABAB

AA

TAA

P

PM

XMM

X

XPP

PP

X

XPPP

PX

PPY

PT is greater thanpredicted by Raoults’s law

PT is less thanpredicted by Raoults’s law

ForceA-B

ForceA-A

ForceB-B< &

ForceA-B

ForceA-A

ForceB-B> &

Fractional Distillation Apparatus

Boiling-Point Elevation & Freezing-Point Depression

Tb = Tb – T b0

T b , T f is the boiling (freezing) point of the pure solvent

0

Tb , Tf is the boiling(freezing) point of the solution

Tb = Kb m

m is the molality of the solution

Kb , Kf is the molal boiling(freezing) -point elevation(depression) constant (0C/m)

Tf = T f – Tf0

0

Tf = Kf m

Gibbs Free Energy and Temperaturefor solid, liquid, vapor, solution

Gib

bs F

ree

Ene

rgy

solid

liquid

vapor

solution

TemperatureTfTf0 Tb

0 Tb

What is the freezing point of a solution containing 478 g of ethylene glycol (antifreeze) in 3202 g of water? The molar mass of ethylene glycol is 62.01 g. Kf water = 1.86 0C/m

Tf = Kf m

m =moles of solute

mass of solvent (kg)= 2.41 m=

3.202 kg solvent

478 g x 1 mol62.01 g

Tf = Kf m = 1.86 0C/m x 2.41 m = 4.48 0C

Tf = T f – Tf0

Tf = T f – Tf0 = 0.00 0C – 4.48 0C = -4.48 0C

Osmotic Pressure ()

Osmosis is the selective passage of solvent molecules through a porous membrane from a dilute solution to a more concentrated one.

A semipermeable membrane allows the passage of solvent molecules but blocks the passage of solute molecules.

Osmotic pressure () is the pressure required to stop osmosis.

dilutemore

concentrated

HighP

LowP

Osmotic Pressure ()

= MRT

M is the molarity of the solution

R is the gas constant

T is the temperature (in K)

A cell in an:

isotonicsolution

hypotonicsolution

hypertonicsolution

Colligative Properties of Nonelectrolyte Solutions

Colligative properties are properties that depend only on the number of solute particles in solution and not on the nature of the solute particles.

Vapor-Pressure Lowering P1 = X1 P 10

Boiling-Point Elevation Tb = Kb m

Freezing-Point Depression Tf = Kf m

Osmotic Pressure () = MRT

Colligative Properties of Electrolyte Solutions

0.1 m NaCl solution 0.1 m Na+ ions & 0.1 m Cl- ions

Colligative properties are properties that depend only on the number of solute particles in solution and not on the nature of the solute particles.

0.1 m NaCl solution 0.2 m ions in solution

van’t Hoff factor (i) = actual number of particles in soln after dissociation

number of formula units initially dissolved in soln

nonelectrolytesNaCl

CaCl2

i should be

12

3

Boiling-Point Elevation Tb = i Kb m

Freezing-Point Depression Tf = i Kf m

Osmotic Pressure () = iMRT

Colligative Properties of Electrolyte Solutions

A colloid is a dispersion of particles of one substance throughout a dispersing medium of another substance.

Colloid versus solution

• collodial particles are much larger than solute molecules

• collodial suspension is not as homogeneous as a solution

The Cleansing Action of Soap

C15H31 사슬

COO- 기

The Cleansing Action of Soap

Grease Hydrophilic Head

Hydrophobic Tail

Chemistry In Action: Desalination

>26 bar

13 장 용액의 물리적 성질 - 요약

• 구성과 구성비 ( 농도 )• 용해와 용해도• 총괄성

용액의 물리적 성질 - 균일 혼합물의 구성

• 용액 - 균일 혼합물• 구성물 – 용매 , 용질• 구성비 – 농도 - 물리적 표현 , 화학적 표현• 농도 단위 - 몰 [M], 몰랄 (m), 몰분율 (X)• 구성 한계 - 용해도

용액의 물리적 성질 - 용해

• 용해와 용해도 - 포화 , 불포화 , 과포화• 용해과정의 분자적 고찰 - 용질 , 용매 분자간

상호작용• 용해도에 미치는 온도의 영향 - 재결정

• 기체의 용해도에 미치는 압력의 영향 – Henry’s Law

• 용해도에 미치는 온도의 영향• 액체의 경우 - 재결정• 기체의 경우

용액의 물리적 성질 - 총괄성

• 총괄성 – Raoult’s Law, van’t Hoff factor• 분압 ,• 끓는점• 녹는점• 삼투압

• 분별증류• 분자량측정• 역삼투