Solutions(dilute) Concentration units M= molaritymoles of solute L of solution X= mol fraction mol...
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Transcript of Solutions(dilute) Concentration units M= molaritymoles of solute L of solution X= mol fraction mol...
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
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