practical course in general and ... - semmelweis scholar
TRANSCRIPT
1
• Physical methods for purification of inorganic substances
- Sublimation
Practical course in general and inorganic chemistry I.
Dr. Szabolcs Béni
13. September 2011.
http://www.gytk.sote.hu/gyki/Oktatok/BeniSzab/BeniSzabolcs.htm
• States of matter, phases
• Phase transitions, Gibbs' phase rule
Most of the slides can be downloaded
- Recrystallization
- Distillation (ideal/nonideal mixture, azeotropism)
States of matter I.
Solid - crystalline
State of matter
- amorphous
Localization; motion of entities e.g.
Long-lasting well-defined, regular shape;
oscillations
NaCl, I2quartz
No definite structure; oscillations glass,amorphous S
2
Liquid crystal(mesomorph phase)
Entity can move (1 or 2 directions)
or spin (1D)
LCD
States of matter II.
State of matter Localization; motion of entities e.g.
Liquid
State of matter
Entities can move, often collide, spin (3D)
Fixed volume, but no fix shape
Gas Disordered motions (rapid flight) , spin,
collisions are rare
Supercritical fluid
(high T, p)
• supercritical CO2 (T > 31°C, p > 7,3 MPa)
• supercritical H2O (T > 374 °C, p > 22 MPa)
- e.g. extraction of caffeine from green coffe beans,
or nicotine from tobacco plant
States of matter III.
Localization; motion of entities
Unique ability to diffuse through solids like a gas,
and dissolve materials like a liquid.
Minor change in T, or p readily change in density
- washing without water!
3
Plasma:
overheated,
ionized gas
molecules → atoms → cations and free electrons
electrically conductive
„plasma fountain”
Analytical ICP
State of matter
States of matter IV.
Localization; motion of entities
Important definitions to understand phase-transitions
• phase: ~ is a set of states of a macroscopic physical system
that have relatively uniform chemical composition and physical properties
• vapor pressure: the pressure of a vapor in equilibrium with its non-vapor
(condensed) phases in a closed system at a given temperature. Units: bar,
atm, mmHg, Pa
If there are two regions (abrupt change in physical properties) in a chemical
system that are in different states of matter, then they must be different
phases:
• Do not confuse with states of matter! (differences between gases, liquids…)
4
Nomenclature for the different phase transitions
Phase diagram of water
TP
liquid
solid
p (kPa)
T (°C)
gas
0
CP
0.0076
0.61
100
22000
374100
Supercriticalfluid
Mt. Everest 8850 m
75
38
5
The Gibbs’ phase rule
F = C− P + 2
P = number of phases
that cannot be shared
F = number of degrees of freedom
C = number of components
• Only one phase exists (P=1):
F = 1 - 1 + 2 = 2 (p and T)
liquid
solid
gasTP
p
T• When two phases are in equlibrium (P=2):
F = 1 - 2 + 2 = 1 (p or T)
A
B
CP
• At the triple point:
F = 1 - 3 + 2 = 0 (only at 0.0076 °C and 0.61 kPa)
C
D
The phase diagram of CO2
TP
liquid
solid
p (kPa)
T (°C)
gas
-78.1
CP
-56.6
517
100
7300
31
Dry Ice (solid CO2)
can sublimate at
atmospheric pressure !
6
Systems with more components
Mixtures
Heterogeneous mixture (more phases)
Homogeneous mixture: (only one Phase, uniform throughout)
Gas mixture Liquid mixture solution: solute is dissolved insolvent
(solid solution)
Suspension, emulsion
Liquid solution
of a gas of a liquid of a solid
CO2 in water
• saturated solution: when no more of a solute can be dissolved into a solvent
• solubility: the concentration of a saturated solution at a given temperature,
e.g. 19 g H3BO3 / 100 g water or S = 3,5 mol/dm3 (M)
ethanol in water sugar in water
7
Purification of salts by recrystallization
• requirement: two solids (salts) can be separated from one another
by recrystallisation if the temperature dependence of
their solubility differs sufficiently in the given solvent.
1. The slightly soluble impurities can be filtered out from the hot solution
2. Those impurities which are well soluble in the solvent (even in cold
solvent) remain dissolved in the mother-liquor after cooling.
• The yield of the first fraction: %100salt dissolved
crystal1
m
m=η
0
20
40
60
80
100
0 10 20 30 40 50 60 70 80 90 100
szénpor
CuSO4
KAl(SO4)2
Old
ható
ság
(g /
100
g ví
z)
T (°C)
Purification of contaminated alum by recrystallization
Charcoal powder
So
lubili
tyw
ate
r
8
Liquid-vapour equilibria
• All liquids have a tendency to evaporate to a gaseous form.
• „A” liquid is more volatile than „B”, if pA > pB and TA* < TB
* (boiling point)
Ideal binary mixtures
•
•
BA
A
A+
=nn
nx
• Dalton’s -law:
Partial pressure of A: Partial pressure of B:
• Raoult’s law (1887):
• At any given temperature there is a partial pressure
at which the gas is in dynamic equilibrium with its liquis form.
5
6
7
8
9
10
11
12
13
14
15
0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1
Öss
sz gőzn
yom
ás (
kPa)
A benzol móltörtje, x B
Vapor pressure of benzene-toluene mixture
*Ap
*Bp
T = 20 °C
Mole fraction of B
To
tal vap
or
pre
ssu
re
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The distillation apparatus
1. Heater
2. Mixture + anti-bumping
granules
3. Distilling flask
4. Condenser
5. Cooling water out
6. Cooling water in
7. Receiving flask
8. Distillate
9. Thermometer/boiling point temperature
75
80
85
90
95
100
105
110
115
0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1
For
rásp
ont
(°C
)
A benzol móltörtje, x B
Liquid-vapor equilibrium for benzene-toluene mixture: boiling temperature vs. composition
*BT
at atmospheric pressure
(100 kPa)*AT
Mole fraction of benzene
Bo
ilin
gpo
int
10
75
80
85
90
95
100
105
110
115
0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1
For
rásp
ont
(°C
)
A benzol móltörtje, x B
Fractional distillation of benzene-toluene mixture
*BT
*AT
Mole fraction of benzene
Bo
ilin
gpo
int
at atmospheric pressure
(100 kPa)
Distillation apparatus
Simple distillation apparatusfractional distillationapparatus
11
Columns for fractional distillation
Vigreux-column
Typical industrial fractional distillation columns
12
Nonideal mixture: distillation of HCl
• HCl ↔ H2O interaction is stronger, than HCl ↔ HCl and H2O ↔ H2O
90
95
100
105
110
0,00 0,05 0,10 0,15 0,20 0,25 0,30
Hő
mér
sékl
et (
°C)
A HCl tömegtörtjeMole fraction of HCl
Te
mp
era
ture
at atmospheric pressure
(100 kPa)