solutions(dilute) concentration units m= molaritymoles of solute l of solution x= mol fraction mol...

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Solutions (dilute) Concentration units M = molarity moles of solute L of solution X = mol fraction mol of solute mol solute + mol solvent weight % mass of solute mass of solution x 100 m = molality moles of solute kg solvent

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Solutions (dilute)Concentration units

M = molarity moles of soluteL of solution

X = mol fraction mol of solutemol solute + mol solvent

weight % mass of solutemass of solution

x 100

m = molality moles of solutekg solvent

Henry’s Law

pressure and solubility of gases

P = kH X kH

O2 4.34 x 104 atm

N2 8.57 x 104 atm

1 atm = 8.57 x 104 Xnitrogen

[N2] = 0.65 x 10-3 M

8.9 atm = 8.57 x 104 Xnitrogen

[N2] = 5.8 x 10-3 M

if gases react with water

NH3 (g) + H2O NH4+ (aq) + OH- (aq)

(water)

CO2 (g) + H2O H2CO3 (aq)

4O2(g) + Hb Hb(O2)4

Vapor Pressure of Solutions

vapor pressure of liquid

pure solvent solute

evaporation condensation

qualitatively

fewer solvent moleculesat surface

water 25oC Pwater = 23.76 torr

add 162 g sugar to 1.0 L

Psolution = 23.57 torr

Raoult’s LawPsolution = Po

solvent Xsolvent

water 25oC Pwater = 23.76 torr

add 162 g sugar to 1.0 L

Psolution = 23.57 torr

Raoult’s LawPsolution = Po

solvent Xsolvent

Xsolvent = Psolution

Posolvent

= 23.57

23.76

Xsolvent = 0.992 = nwater

nwater + nsugar

1.0 L = 1000 g

18.02 g/mol= 55.51 mol

0.992 = 55.5155.51 + x

x = 0.44 molsugar

162 g sugar0.44 molsugar

= 365 g/mol molecular weight of sucrose

Powater Psolution> = Po

water Xwater

Raoult’s Law

Psolution == PoA XA

two volatile components

+ PoB XBgas

liquid

PA

XA1

(torr)22

0

PB

(torr)

75

XB 10

Ptotal

mix 80 mol A + 20 mol B

What is Ptot ?

PoA= 22

PoB= 75

XA = 0.8

XB = 20/(80+20)= 0.2

17.6 + 15.0 = 32.6

XB = PB

PA + PB

= 15.032.6

= .36

= 80/(80+20)

Ptot =

= PA + PB Daltons Law

Fractional Distillation

Ptoluene

Xtoluene1

(torr)22

0

Pbenzene

(torr)

75

Xbenzene 10

Ptotal

Potoluene = 22

Pobenzene = 75

Xtoluene = 0.8

Xbenzene = 0.2Xbenzene = .36

Xtoluene = .64

Xbenzene = .36

Xtoluene = .64Po

toluene = 22

Pobenzene = 75

Xbenzene = .66

Xtoluene = .34

Ideal solution

Raoult’s Lawtwo volatile components

benzene toluene

LDF LDF

Ideal solution

LDF

higher vapor pressure

Raoult’s Lawtwo volatile components

acetone water

H-bond

dipole-dipole

non-ideal solutionH-bonding

Vsoln < Vacetone + Vwater

P.E.soln increase

decrease

K.E.soln increase

decreaseTsolution Tcomponents>

IMFsoln > IMFcomponents

Raoult’s Lawtwo volatile components

acetone waternon-ideal solutionnegative deviation

23.8

229

XacetoneXwater

Poacetone Po

water

mixing exothermic

Hmixing < 0

Raoult’s Lawtwo volatile components

CHCl3 C2H5OHnon-ideal solution

positive deviation

59.0

194

XchloroformXethanol

Pochloroform Po

ethanol

H-bonddipole-dipole

dipole-dipole

mixing endothermic

Hmixing > 0

Raoult’s LawPsolution = Po

solvent Xsolvent

lower P of solution boiling point of solutionraise

Tb = b.p. solution - b.p. solvent

Tb = KB m KB molal boiling-point elevation constant

m molality of solution(mol solute/kg solvent)

20 g NaCl 500 mL water What is Tb?

= 0.51 kg K/mol

= 0.34 mol 0.500 kg

Tb = 0.51 kg K/mol x 0.68 = 0.35 K 100.79oC

NaCl electrolyte 2 mol particles / mol formula

Colligative Property

Colligative Property

Tb = KB m i i = moles of particlesmoles of solute

non-electrolyteglucose

i(expected)

i(observed)

1 1

electrolyte

NaCl

FeCl3

HCl

2 1.9

4 3.4

2 1.9

Freezing point depression

Tf = KFm KF molal freezing-point

depression constant

m molality of solution(mol solute/kg solvent)

i

0.05 m NaNO3 0.075 m CuSO4 0.06 m (NH4)2SO4 0.14 m sucrose

Osmotic Pressure

cellular biology molecules across membranes

cell membrane permeable to water

impermeable to protein, etc. = gh

= MRT

most accurate of colligative properties