Transcript PowerPoint 簡報

p.01
Partition of Solute between
2 Immiscible Solvents
“2 phases” in contact
with each other …
solvent 1
solute X
Solute X dissolves in both
solvents 1 and 2. At eqm,
the rate of diffusion from
one solvent to another is
the same as reverse rate.
solvent 2
 conc. of X in 1 and 2 will remain
constant at constant temperature.
C. Y. Yeung (CHW, 2009)
p.02
A new Keq for this system:
KD (partition coefficient)
“distribution of solute in 2 solvents”
X(solvent 1)
X(solvent 2)
at start (conc.)
x
0
at eqm (conc.)
x–a
a
mol dm-3 / g cm-3
KD =
a
x–a
(no unit)
less dense solvent
(usually organic solvent)
more dense solvent
(usually H2O)
CCl4 and CHCl3 are the only two
organic solvents denser than water.
p.03
At 291K, KD of butanoic acid (CH3CH2CH2COOH)
between ether and water is 3.5. Calculate the mass
of butanoic acid extracted by shaking 100 cm3 of
water containing 10g of butanoic acid with 100 cm3
of ether.
how many grams of butanoic acid
could be extracted from water?
ether (100cm3)
butanoic
acid (10g)
H2O (100cm3)
KD (at 291K) = 3.5
1. KD > 1, i.e. butanoic acid
is more soluble in ether
than in water.
2. Butanoic acid could not
be completely extracted
from water by ether.
Let a be the mass of butanoic acid
to be extracted by ether,
At eqm:
KD = 3.5 =
a/100
(10-a)/100
a = 7.78
 7.78g of butanoic acid will be
extracted.
p.04
p. 108 Check Point 16-8A
CH3CCl3
(100cm3)
A (6g)
KD = 15
H2O (60cm3)
Let a be the mass of A to be
extracted by CH3CCl3,
At eqm:
KD = 15 =
a/100
(6-a)/60
a = 5.77
 5.77g of A will be extracted.
p. 128 Q. 16
(a) Let a be the mass of A to be
extracted by H2O,
H2O(50cm3)
At eqm:
KD = 49.3 =
lactic acid
(8g)
CHCl3 (100cm3)
KD = 49.3
a/50
(8-a)/100
a = 7.69
 7.69g of lactic acid will be
extracted.
(b) Let x be the mass of A to be
extracted by first 25cm3 H2O,
Let y be the mass of A to be
extracted by another 25cm3 H2O,
At eqm:
At eqm:
KD = 49.3 =
p.05
x/25
(8-x)/100
x = 7.40
KD = 49.3 =
y/25
(8-7.4-y)/100
y = 0.55g
 (7.40 + 0.55) = 7.95 g of lactic acid will be extracted.
p.06
p. 128 Q. 16(c)
Conclusion … ?
“extracting solvent”
Solvent extraction
is more efficient if the
same amount of
“extracting solvent”
(H2O) is added in small
portions several times
instead of all at once.
H2O(50cm3)
lactic acid
(8g)
CHCl3 (100cm3)
KD = 49.3
 The mass of solute extracted by solvent extraction:
50cm3  1
<
25cm3  2
<
10cm3  5
<
5cm3  10
p.04
Application of Partition
Paper Chromatography !
Equilibrium?
distribute
between
mobile phase
stationary phase
layer of water adsorbed
on the filter paper
(stationary phase)
(mobile phase)
(solute)
p.08
How does Paper Chromatography work?
Solvent moves up with the solute.
Different solutes have different KD between the mobile
phase and stationary phase.
Solute with larger KD (more soluble in solvent) will
move faster on the paper when the solvent is soaking
up.
Different solutes could be separated on the filter paper.
“chromotograph”
p.09
Chromatogram
Chromatography is used by the ‘Horse Racing
Forensic Laboratory’ to test for the presence of
illegal drugs in racehorses.
(methanol as solvent)
p.10
p.11
Rf value: calculated from the Chromatogram
In methanol,
Rf of Caffeine = d2/d1
d1
d2
Rf is always smaller than 1.
It is possible to characterize
a particular compound
separated from a mixture by
its Rf value. (ref.: p. 109)
p.12
Expt. 11 Distribution of ethanoic
acid
between butan-1-ol and water
2M ethanoic acid
(10cm3)
butan-1-ol shaked
(25cm3)
water
(40cm3)
10cm3 sample
from organic layer
+ 25cm3 H2O
+ phenolphthalein
titrated
against
std. NaOH
 Vorganic
titrated
10cm3 sample from
against std.
aqueous layer
NaOH
+ phenolphthalein
 Vaqueous
separating funnel
p.13
Repeat expt. With different vol. of
CH3COOH, butan-1-ol and water ….
Vorganic
Vaqueous
KD =
v1
vi
[CH3COOH]organic
[CH3COOH]aqueous
Therefore …
v2
vii
=
v3
viii
v4
viv
(Vorganic  [NaOH]) / (10/1000)
(Vaqueous  [NaOH]) / (10/1000)
Vorganic
slope!
Vaqueous
=
Vorganic
Vaqueous
p.14
Assignment
p.128 Q.14, 15, 17
p.230 Q.6(b), 12(b), 14 (a), (c)
[due date: 19/3(Wed)]
Next ….
Acid-Base Eqm: Arrhenius Theory &
Bronsted-Lowry Theory, Kw & pH
(p. 130-137)