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Physical and analytical
chemistry
Physical
and Analytical
Chemistry
Medical Chemistry
and
Biochemistry
Institute of Medical
Biochemistry
term
Medical Chemistry and Winter
Biochemistry
Category I
© Institute of Medical Biochemistry, 1st Faculty of Medicine,
© Institute of Medical Biochemistry and Laboratory Diagnostics
of the General
University
Charles University
in Prague,
2005-12 Hospital and of The
First Faculty of Medicine of Charles University in Prague - 2005-2016
Chemical bond, importance of its character for
the properties of biological compounds
Bond – sharing of electron pairs between binding
elements
 Character of the bond is given by the difference of
the electronegativities of the elements, which take
part in the bond. There are many types of bonds
between two extremes – totally non-polar bond (in
one-element molecules) and ionic bond (one
binding electron from the first atom is completely
attracted to the other atom) (with exception of the
metallic bond – less important in biology )

Electronegativity: empirically found number, expressing the
ability of the atom to attract the binding electrons of a covalent
bond
Phys. and Anal. Chem. 2015/2016
3
Types of bond
Metallic bond: (specific conductivity DC or low frequency field
<1.106> -1cm-1 (=conductor), cations are fixed,
conducting electrons are in electron cloud, it is not
possible to determine which electron belongs to concrete
cation
Covalent bond: realized by shared pair of electrons (400-600
kJ/mol). (Each partner 1 e- or donor-acceptor bond)
Ionic bond: Coulombic forces (attraction)
Intermolecular forces:
 Van der Walls forces (4-8 kJ/mol) (a) coulombic forces
(dipole is permanent) b) inducting (dipole is inducted) c)
dispersed (center of gravity is dispersed - + and – charges
are separated)
 Hydrogen bridge (20-30 kJ/mol) – dipole-dipole bond
Phys. and Anal. Chem. 2015/2016
4
Coordination compounds
Donor-acceptor bond: NH3
N
H
H
2s  2p 
1s


2s2 2p3

1s
[Fe2+(CN)6]4-,
[Fe3+(CN)6]3-,
Fe(CO)5,
[Cu+ (NH3)2]+,
[Cu+(CN)2]-,
[Cu2+(H2O)4]2+,
[Cu2+(NH3)4]2+,

1s
H
Examples:

d
Cu0 3d
    
4s 
Cu2+ 3d
   
4s NH3 4p NH3 NH3 
dsp2
NH3
Phys. and Anal. Chem. 2015/2016
4p
5
Coordination compounds
Ligand
Ligand
Central atom
Ligand
Central atom
Ligand
Mononuclear
Polynuclear
Phys. and Anal. Chem. 2015/2016
6
Chelates
Two or more donor atoms of the same ligands on one central
atom
OH
C
O
OH
CH2
CH2
N
C
CH2
CH2
N
CH2
CH2
O
CH2
CH2
OH
OH
C
N
CH2
C
DTPA
O
OH
C
O
O
Chelaton I
Chelaton II (=EDTA=ethylenediaminetetraacetic acid)
Chelaton III (=EDTA=disodium salt of ethylenediaminetetraacetic acid)
Chelaton IV (=DTPA=diethylenetriaminepentacetic acid)
H2 O
H2O
H2O
DTPAH
H2 O
OH-
H2 O
O
O
Cr III+
O
C
O
C
X
-OOC
DTPAH
Phys. and Anal. Chem. 2015/2016
COO-OOC
7
Hydrogen bridge
 Relatively weak interaction between atom of hydrogen, which exhibits deficit of electron
density, and other atom, which exhibits surplus of electron density; the electrons are
attracted from one atom to another.
 The deficit of electron density on the hydrogen atom is formed, when the atom is chemically
bond to a more electronegative atom. For example: Hydroxyl group (-O-H). Oxygen has a
relatively high electronegativity, therefore it attracts the electron pair, which is shared in the
bond with hydrogen. A dipole is formed, i.e., non-symmetric distribution of the charge; the
electrons are nearer to the oxygen atom, this has a partially negative charge, while the
hydrogen atom exhibits lack of electron density, it exhibits a partially positive charge.
 If such hydrogen atom, which “sticks out“ from its molecule on the edge of its OH-group, is
situated in the neighborhood of another electronegative atom, which attracted the electrons
from other chemical bond and it gained a surplus of electrons and a partially negative
charge, there will arise the attractive forces between partially positively charged hydrogen
and its partially negatively charged partner. This is the principle of hydrogen bridge
formation.
molecule -- O - H ....... O -- molecule
molecule -- O - H ....... N -- molecule
molecule -- N - H ....... O -- molecule
molecule -- N - H ....... N -- molecule
Connection of peptide chains by hydrogen bridges
Phys. and Anal. Chem. 2015/2016
8
Electronegativity: empirically found number, expressing the
ability of the atom to attract the binding electrons of a covalent
bond
XA-XB=0,21  ΔD, kde ΔD=DAB-( DAA DBB )
D…dissociation energy, X … Electronegativity
Ionicity
I=100 (1-exp[-0.21(XA-XB)2])
Examples: XNa= 0.9 XCl=3.1
=> XCl-XNa=3.1-0.9=2.2
=> I = 64 %  I > 50 %  ionic bond
XH= 2.15 XCl=3.1
thus XCl-XH=3.1-2.15=0.95
=> I = 18 %  I < 50 %  covalent bond, polar
Phys. and Anal. Chem. 2015/2016
9
Bond polarity
Bond polarity has great biological importance in compounds.
General rule: compound with low polar bond easily reacts with
other low polar compounds, whereas polar compounds have
higher affinity to other polar and ionic compounds. Therefore
non-polar solvents have high affinity to nervous tissue
(containing large amount of non-polar lipoid compounds,
whereas polar and ionic compounds are very good soluble in
aqueous solutions (blood plasma, lymph, coeliolymph).
Bond distance
l(Si-C)=l(C-C)/2 + l(Si-Si)/2 = 154/2 + 234/2 = 194 pm –
covalent bond
l(A-B)=l(A-A)/2 + l(B-B)/2 – 0.9 (XA-XB) - polar bond
The bond is shortened by: multiplicity, hybridization
Phys. and Anal. Chem. 2015/2016
10
Ionic compounds are best soluble in water and they are very
good absorbed from alimentary tract; generally, they have
faster and stronger biological effects, than the worse
absorbable low-polar compounds.
Non-polar compounds are more effective by inhalation
(narcosis, general anesthesia), where they can interact (on the
large surface of the lung) with the lipoid parts of the blood
(biomembranes of erythrocytes, lipoproteins of blood plasma).
Phys. and Anal. Chem. 2015/2016
11
Bond polarity - dipole
a) Two-atomic molecules: dipole moment p=.l (charge . bond distance)
b) Polyatomic molecules: vector sum of dipole moments of all bondS in
the molecule
The polarity of the solvent is characterized by relative permittivity (dependent on the temperature)
Compound
H2O
NH3
HCN
H2S
HF
HCl
HBr
KI
KF
Dipole moment p.1030 [C.m-1]
6.15
4.88
9.79
3.67
6.08
3.57
2.64
30.86
28.72
1 Debay = 3.34.10-30 C.m-1
Phys. and Anal. Chem. 2015/2016
12
Mixotropix scale of solvents
Hydrophilic
Water
Methanol
Ethanol
Acetone
Phenol
n-Butanol
Ethylacetate
Diethyl ether
Trichlormethane
Benzene
Tetrachloromethane
Cyclohexane
Hexane
Paraffin oil
Hydrophobic
Solvents:
1. Lipophobic Limited miscibility of solvents +
1. Inorganic
Different solubility ► Extraction
2. Lipophilic (Distribution coefficient)
2. Organic
Phys. and Anal. Chem. 2015/2016
13
Water – properties I.
H2O Electronegativity:
O
-
3.5
H
-
2.2
Difference
1.3
The bond between O and H is strong polar (dipole moment
p=6.15.10-30 Cm-1=1.8 Debay)
Arrangement of H2O - molecule
Tetrahedron, two free electron pairs, two nucleus of
hydrogen
a)
Solid- Ice
b)
Liquid-water
Unbinding electron pairs
Binding angle (104.5o) influenced by free electron pairs. Distance 96 pm.
Phys. and Anal. Chem. 2015/2016
14
Water – properties II.
The polarity of water molecule is very high
It influences essentially its properties:
Comparison with H2S (Electronegativity S = 2.6):
Boiling point [oC]
H2O
100
H2S
-63.5
Fusion point [oC]
0
-91
These pronounced differences are
caused by the formation of hydrogen
bridges among molecules.
Phys. and Anal. Chem. 2015/2016
15
Water – properties III.
Formation of hydrogen bridges is the source of water anomaly, which probably have
enabled (affected) the life in such form as we know it today.
In a solid state, water has a highly oriented crystalline structure (hexagonal), in which each
molecule of water is surrounded by four other molecules of H2O, which are connected by
hydrogen bridges (There are about 7 various modifications – pressure, temperature).
Thereby relatively large free spaces are formed, the ice has lower density and it swims on
water.
Due to the polarity of the molecule and ability of formation of hydrogen bridges water
represents the ideal solvent for ionic and polar compounds.
Phys. and Anal. Chem. 2015/2016
16
Solution
(dispersion system, macroscopically homogenous)
Solution – one-phase system, which is composed minimally from
two individual substances
a)
gaseous (air)
b)
liquid (drinking water)
c)
solid (metallic alloys, glass)
a) and b) are fluids
Solutions are dispersion systems
Dissolution of compounds = their mutual permeation on the
molecular level, i. e., permeation of building elements (molecules,
ions) – original components, often new bonds are formed
(associates).
Phys. and Anal. Chem. 2015/2016
17
State
State
Gas
Liquid
Symbol
g
l
Solid
Plasma
S
System – phases
1) Compounds (system) physically homogeneous – 1 phase
2) Compounds (system) physically heterogeneous – more phases
The Area, where the phases are in contact, is called interface. The
processes on the interfaces are very important for analytical
chemistry (chromatography, polarography, voltammetry,
electrochemistry generally), likewise for biology and medical
sciences (e.g., biomembranes, colloid chemistry and chemistry of
the cell).
Phys. and Anal. Chem. 2015/2016
18
Water – properties IV – dissolution
Solvatation (hydration) of molecules is
realized through the formation of hydrogen
bridges by dissolution of non-ionic
compounds. For example the dissolution of
urea (NH2-CO-NH2)
(High-molecular biomolecules – peptides,
nucleic acids)
O
H
O
O
H
H
H
O
H
O
H
O
H
H
H
or glucose
H
OH
H
OH
O
H
H
O
H
H
HO
HO
H
N
O
H
H
O
H
N
O
H
H
H
H
CH2
O
H
C
H
H
OH
H
Similar molecule of cyclohexane
cannot form hydrogen bridges and
therefore is not soluble in water.
H
Phys. and Anal. Chem. 2015/2016
19
Water as solvent
1.
Low-molecular compounds, the bonds are either
non-polar or weak-polar, covalent – in solution
there is no any change of configuration –
solvatation occurs (molecules are surrounded by
molecules of solvent, Van der Walls bonds)
2.
Dissolved compound produces a system with the
solvent, in which the particles are in ionized form
– the solution is electrically conductive –
electrolytes:
a)
real (true) (Na2SO4 in H2O)
b) potential (H2SO4 in H2O)
Fig. Dissolution schema
a)
b)
c)
Compound is non-electrolyte, the molecules are solvated;
Compound is real (true) electrolyte, during the dissolution are the ions dispersed among
molecules of solvent;
Compound is potential electrolyte, its originally polar covalent molecules are ionized
and dispersed among molecules of solvent
Phys. and Anal. Chem. 2015/2016
20
Solubility of oxides
Acidic oxides
(soluble)
basic oxides
(soluble)
Insoluble oxides
Phys. and Anal. Chem. 2015/2016
21
Solubility of hydroxides
Soluble
oxoacids
soluble
hydroxides
Insoluble
hydroxides
Phys. and Anal. Chem. 2015/2016
22
Solubility of phosphates, carbonates, sulfites
Phosphates,
carbonates,
sulfites are not
formed
soluble
Insoluble
Phys. and Anal. Chem. 2015/2016
23
Solubility of halides
Phys. and Anal. Chem. 2015/2016
24
Solubility of sulfides
soluble
Insoluble
Phys. and Anal. Chem. 2015/2016
25
Solubility of solid substances
Solubility is defined as maximal amount of the compound soluble in 100 g of water
under given temperature
Phys. and Anal. Chem. 2015/2016
26
Dispersion systems I
Dispersion Gaseous
medium
Liquid
Solid
Solid foams
(inclusion)
(foam glass, rubber,
plastics)
Dispersion
particles
Gaseous
Mixture of
gases (air)
Foam
Solutions of gasses
in liquids
Liquid
Aerosols
(fog)
(medicine)
Emulsion (milk,
dressing) –
solutions of liquids
in liquids
Solid
Smoke
(medicine)
Suspension (blood)
Lyosols and
colloidal solutions
Solution of solid
particles in liquids
Phys. and Anal. Chem. 2015/2016
Solid mixtures;
solid solutions
(alloys, glass)
27
Dispersion systems II
Type of the mixture
Coarse
dispersion
Colloidal solution Real
solution
Size of dispersed particles
>1000 nm
>1 nm < 1000 nm
< 1 nm
Upper limit of particle size in colloidal
solutions is not sharp (100-1000 nm)
Almost nontransparent
Turbidity,
refractometry
Clear
The particles are
sedimented in
ultracentrifugal
machine, they do not
go through special
membrane filters,
their diffusion is
slow, it is possible
see them in electron
microscope;
opalescent
It is not
possible to
separate
them in
centrifugal
machine,
go through
all filters;
diffusion is
very fast
Separation Sedimentation in gravitation field, the
particles do not go through paper filters, it is
possible to see the particles in optical
microscope
For example blood:
The sedimentation rate of blood can indicate disorder
processes. Increased values (i.e., increased rate of
blood sedimentation) are registered in case of
disorders characterized by increase of globulins
(inflammations, bacterial infection, anemia, some
carcinogens). Decreased values (decreased ability of
blood sedimentation) in case of abundance of
corpuscles (polyglobulia) and in case of lack of
globulins.
Phys. and Anal. Chem. 2015/2016
28
Solubility of solid compounds in liquids
If the amount of solid compound is high enough, the
equilibrium between two phases is established - generally
between unsolved (solid) compound and saturated (liquid)
solution. This equilibrium depends on the temperature. Dissolved
compound can be in the undissociated, partly dissociated or
completely dissociated form.
In case of partial dissociation the following equilibrium is
established BAB++A- and it is valid:
Phys. and Anal. Chem. 2015/2016
29
Activity – activity coefficient
i 1
ai=ci.i, kde clim
0
where a… activity, γ… activity coefficient
i
pH = -log aH+ = -log (c H+.H+)
c(HCl)
[mol.L-1]
(HCl)
pH = -log(c HCl.HCl)
pH = -log(cHCl)
0.001
0.966
3.02
3.00
0.1
0.796
1.10
1.00
1
0.809
0.09
0.00
c (H2SO4)
[mol.L-1]
(H2SO4)
pH = -log(2.cH2SO4.H2SO4) pH = -log(2.cH2SO4)
0.001
0.803
2.79
2.70
0.1
0.265
1.28
0.70
1
0.130
0.59
-0.30
*Other definition of activity: ai = xi.i, where xi denotes molar fraction
Phys. and Anal. Chem. 2015/2016
30
Dissociation, dissociation constant
AB  B+ + A-
lim  i  1 where a… activity, γ… activity coefficient
ai=ci.i,
ci  0
*Other definition of activity: ai = xi.i, where xi denotes molar fraction
K BA a

a B  a A
a AB

B A  

.


AB
B

A

 AB
generally BAB++A- K BA  B
B A

B  A  
 KA

AB
 AB

 A 
B A 
 

 


 
   
 


 
KBA…dissociation constant
Phys. and Anal. Chem. 2015/2016
31
Solubility of solid compounds in liquids II
Heterogeneous equilibrium between solid compound and its
solution:

BA L
K
BA S

B A  AB

.

=>
KK BA

L
AB ABS
S…Solid; L … Liquid
[BA]  [BA]L and [BA]s is redundant, i.e., const., and therefore:
[B+][A-] = [BA]S.K.KAB =SBA – (concentration) solubility product
Total analytical concentration is the sum of concentrations of undissociated
and dissociated parts. Because the activity of solid component is constant [BA] = 1 therefore: SBA=[B+].[A-] – (concentration) solubility product
In other words: It is the equilibrium constant for the equilibrium, which exists
between the slightly soluble salt and its ions in the saturated solution.
(Significant in biology: mineralization of teeth and bones, practically
reversed process).
Phys. and Anal. Chem. 2015/2016
32
Concentration solubility product at 25 oC
Phys. and Anal. Chem. 2015/2016
33
Ionic strength
1
   ci zi2
2 i
ci … ion concentration; zi … ion charge
Compound (1 mol.L-1)
I
NaCl
½(1. 12+ 1(-1)2)
1
MgCl2
ZnSO4
FeCl3
K4Fe(CN)6
½(1.22+2. (-1)2)
½(1.22+1.(-2)2)
½(1.32+3. (-1)2)
½(4.12+1. (-4)2)
3
4
6
10
Mg3(PO4)2
½(3.22+2. (-3)2)
15
In case of weak electrolytes it is necessary to calculate the
concentrations of ions from dissociation grades and their values to use
for calculation of the ionic strength.
Phys. and Anal. Chem. 2015/2016
34
Activity-coefficient
 log  i  0.5092. z z 
 log  i  0.5092. z z
 log  i  0.5092. z z
 log  i  0.5092. z z

1 

1  d .B 

1  d .B 
 C
(B,C…constants, d…diameter of ions)
Phys. and Anal. Chem. 2015/2016
35
Activity coefficient γ± at 25 oC
Phys. and Anal. Chem. 2015/2016
36
Ionic strength II
K BA a
B A
 KA
 AB


pK A  ( pK A ) a  log  B   log  A  log  AB
pK A  ( pK A ) a  N

1 
Very important for adjustment of buffers and analyzed
solutions to constant (specified) ionic strength.
Reaction
A=C- + D+
N
+1
Reaction
A± + B = C + D±
N
0
A-=C2- + D+
+2
A2± + B = C± + D±
-1
A2-=C3- + D+
A3-=C4- + D+
+3
+4
A3± + B = C2± + D±
A4± + B = C3± + D±
-2
-3
Phys. and Anal. Chem. 2015/2016
37
Colloidal solutions I
(in biology practically always aqueous colloids)
A) Lyophilic
B) Lyophobic C) Micellar
A. Lyophilic: in most cases solutions of macromolecules – polymers – which
have high affinity to the molecules of the solvent, thus the particles, which
could be in given liquid solvated (solvation shell is formed – particles are
surrounded by solvent molecules). In medicine, the most important
hydrophilic biopolymers are peptides, nucleic acids and polysaccharides,
which attract large amount of water.
B. Lyophobic: particles, which in given system are not surrounded by solvent
(e.g., hydrophobic). They are formed by aggregation of low-molecular
compounds in solution or by dispersion of solid particles in solvent. Their
stability is given mainly by electric charges of dispersed particles. They
coagulate easily, e.g., by addition of the electrolyte. Its stability is limited.
The stability can be increased or decreased by addition of lyophylic colloids
(small addition labilizes, higher amount stabilizes lyophobic colloids).
Application: previously investigation methods, at present coloring of peptides
(also in histochemistry).
Phys. and Anal. Chem. 2015/2016
38
Colloidal solutions II
(in biology practically always aqueous colloids)
A) Lyophilic
B) Lyophobic C) Micellar
C.
Micellar: Micelles are formed from molecules, which have polar part as well as nonpolar part – for example soaps or phospholipids (CxHy-SO3-Na+) (CxHy-COO--Na+)
Characterization:
 Critical micellar concentration – minimal concentration, at which the
micelles are formed
[X]in micels [X]in solution
 Mean (average) lifetime of micelle
 Shape of the micelle (spherical, discoidal, lamellar, rod-like, vesicular).
Hydrophobic part
micelle
Hydrophilic part
Phys. and Anal. Chem. 2015/2016
39
Colloidal solutions - sols and gels
Sol - liquid or gaseous colloidal solution; high dispersion system of solid
particles in liquid (fluid) with low concentration of dispersed phase.
According to the interactions between dispersed phase and dispersion medium
we categorize the sols into two groups: lyophilic (attractive interactions) and
lyophobic (repulsive interactions).
1. Liquid: Lyosols (solid compounds in liquid), hydrosols (often only sols)
2. Gaseous: Aerosol (fog - liquid, smoke – solid particles)
Gel – dispersion of solid compound in liquid with high concentration of solid
phase. Dispersed particles are mutually connected, therefore the gels are firm,
consistent (due to Van der Waals forces). It is the special case of colloidal solution,
where the coherent phase is formed by dispersion medium as well as by dispersed
particles. It can be produced from sol by thickening, cooling (e.g., gelatin gel, agar
gel). By stirring is the gel changed into liquid state, but after the stirring is stopped,
it freezes (tixotropy) (ketchup).
Xerogel (e.g., silica gel) – it can be formed from sols as well as gels by very
slow ways of concentration and drying, by high underpressure from deep-frozen
or dispersed materials. It is possible by hydrophobic colloids only. In contact
with water (solvent) it attracts water readily (swells) – e.g., instant coffee in
water, Lyophilization – foods, albumin
Phys. and Anal. Chem. 2015/2016
40
Boiling point elevation, freezing-point depression
The dissolved non-volatile compound elevates the boiling-point and depress its
freezing point in comparison with pure solvent (coligative property … depends on the
number of dissolved particles, their identity is not important)
ΔTE = KE · mB
ΔTt = Kt · mB
ΔTE = TB(solution) − TB(pure solvent),
ΔTt = Tf(solvent freezing point])- T(solution freezing point)
mB=i.c … molality
mB=i.c … molality
c…molar concentration
i…number of ions formed by dissociation
c…molar concentration
i…number of ions formed by dissociation K …Cryoscopic constant
t
Kt…Ebulioscopic constant
RT12 M 1
KE 
H vap,1
RT12 M 1
Kt 
H melt,1
Cryoscopy (Ebulioscopy respectively )…the physical method used for determination of
molar mass of a compound, based on the determination of freezing point depression (boiling
point elevation respectively) of the solvent after dissolving of this compound, which neither
reacts with the solvent nor forms the mixed crystals.
Phys. and Anal. Chem. 2015/2016
41
Change of the temperature of state change by the
change of the pressure
Clausius-Clapeyron equation
 P2  H vap  1 1 
  
ln   
R  T1 T2 
 P1 
T1 , T2 …absolute temperature
P1 , P2 …pressure
R … universal gas constant 8.314 J mol-1K-1
H vap…enthalpy of vaporization
Phys. and Anal. Chem. 2015/2016
42
Filtration, ultrafiltration
Underpressure
filtration
Filtration
Overpressure
filtration
~
Mr>10000
Phys. and Anal. Chem. 2015/2016
43
Mass transport
•
Migration: electric field
•
Convection: stirring, movement
•
Diffusion: transport in consequence of concentration difference
Phys. and Anal. Chem. 2015/2016
44
Diffusion
Spontaneous transport of mass from the place of its higher concentration to the
place of its lower concentration. It is caused by heat transport of the particles. It is
realized until reaching of the equilibrium.
Diffusion is the principle of many important biological processes, e.g., respiration,
water absorption.
The diffusion process is described by two Fick’s laws, which enable calculation
(using measured diffusion rate) of the diffusion coefficient. This can be used for
determination of the size of particles, eventually to determine of their molecular
mass.
Ji 
n j
t
c j
t
  DA
D
 2c j
xi
2
 2c j
xi
2
1st Fick’s law – number of particles j transported
through the area A during the time unit t
2nd Fick’s law – the change of particle concentration
in time and chosen point
Phys. and Anal. Chem. 2015/2016
45
Diffusion coefficient (D)
Stokes-Einstein law for the diffusion of spherical particles, with
radius r, which are transported in medium of given viscosity.
k B .T
D
6 ..r
Compound
D ... Diffusion constant [m.s-1]
kB…Boltzmann constant (R/NA) = 1.380 662(44).10-23 J.K-1
NA…Avogadro's constant 6.022045(31).1023 mol-1
R ... Universal gas constant 8.314 41(26) J.mol-1.K-1
T … Absolute temperature [K]
 ... Dynamic viscosity [kg.m-1.s-1]
r … Diameter of the particles [m]
D . 106
cm2s-1
Compound
D . 106
cm2s-1
Compound
D . 106
cm2s-1
Methanol
16.40
Ribonuclease
1.19
DNA
0.01
Urea
13.50
Hemoglobin
0.69
Glucose
4.90
Ethanol
10.20
Serum alizarin 0.59
Fibrinogen
0.20
Phys. and Anal. Chem. 2015/2016
46
Dialysis
Medical treatment using the small porous semi-permeable membrane
as compensation in case of renal insufficiency. The dialysis solution
on the one side of the membrane removes waste products of
metabolism from blood on the other side of the membrane.
Dialysate is flowing in the same direction as
blood flow in the extracorporeal circuit
concurrent flow
Blood
countercurrent flow
Dialysate is flowing in the opposite
direction to blood flow in the
extracorporeal circuit
Peritoneal dialysis uses a peritoneum for the purposes of dialysis. A man with
catheter in abdominal cavity is maintained in metabolic favorable conditions by
repeated suck in and suck up of dialysis solution. A device called cycler can be used
for these purposes.
Phys. and Anal. Chem. 2015/2016
47
Osmosis I
Transport of solvent (e.g., water) from the solution (e.g., of glucose)
from the point of lower concentration to the solution with higher
concentration through semi-permeable membrane, which transmits
water, but not the molecules of glucose. This transport can be
prevented by outer pressure, which corresponds to OSMOTIC
PRESSURE. The higher the concentration of the solution, the higher
the osmotic pressure. Osmosis through semi-permeable membrane is
realized until the osmotic pressure of solutions on both sides of the
membrane is not equal. Various degrees of permeable membranes are
very common in living organisms (e.g., cell membranes). Osmosis is
very important for controlling water distribution in living organisms.
Osmotic pressure depends on the number of dissolved particles
(molecules or ions) in the solvent unit. Peptides and other compounds
of large molecules produce low osmotic pressure (with respect to its
mass in solution).
Phys. and Anal. Chem. 2015/2016
48
Osmosis II
Osmotic
pressure
Osmotic
pressure
water
water
Hypertonic
shrinking
Isotonic
solution
Phys. and Anal. Chem. 2015/2016
Hypotonic
swelling
49
Osmosis III
=i.RTc
 … osmotic pressure [Pa]
c… concentration [mol.l-1]
R... universal gas constant [8.314 41(26) J.mol-1.K-1]
T… Temperature [K]
i … isotonic coefficient
i = 1+(n-1)
… ionization grade
n … number of molecules originated by ionization, dissolution,
etc.
(NaCl … = 0.863, n = 2, therefore i = 1.863)
Isotonic infusion solution of sodium chloride
(0.9 % m/V, i.e. 0.154 mmol.L-1)
Phys. and Anal. Chem. 2015/2016
50
Donnan equilibrium
Free transport water
Intracellular| Membrane
|Extracellular
On both sides of the membrane is the equal number of positively and negatively charged
ions (8+=7-+1-) and (3+=3-) (electroneutrality); diffusible electrolyte is distributed
uneven.
In compartment with undiffusible anions is higher concentration of cations, whereas
concentration of anions in this compartment is lower, than in the compartment, which
does not content them (or their number is lower).
By the computation it is necessary to take into account the total or semi permeability of
the membrane.
Phys. and Anal. Chem. 2015/2016
51
Membranes
E1 = φsolution L– φmembrane edgeL
E2 = φmembrane edgeL – φinside of membrane
E3 = φinside of membrane– φmembrane edgeR
E4 = φmembrane edgeR – φsolutionR
1. Distribution (Nernst) potential – permeable membrane
2. Donnan potential – semi-permeable membrane
3. Membrane potential
a) Diaphragm (>100 nm)
b) Fine porous membranes (1-100 nm)
c) Microporous membranes (<1 nm)
Phys. and Anal. Chem. 2015/2016
52
Autoprotolysis of water I
H +
H
H
2H2O
O
O
H
H
+ OH -
O
H
H
In reality
H
H
-
+
H
O
O
H
H
H
+
O
H
H
H
O
H
O
O
H
H
H9O4+;
H
O
H
H
H
O
H5O2+; H7O3+
Phys. and Anal. Chem. 2015/2016
H7O4-
53
Autoprotolysis of water II – Ionic product of water
pH = -log aH+  -log [H+]
H2O=H++OH-

H OH  H OH 
K

 1.8.10


H 2O


16
55.56
Kv=K.[H2O]= [H+] [OH-] = 1.8·10-16.55.56 = 1·10-14 mol2.dm-6
pKv = -log (Kv) = 14
[H+] = Kv / [OH-] =1·10-14 mol2.dm-6 / [OH-]
[H+] = [OH-] =  Kv = 1·10-7 mol.dm-3
pHv = -log ([H+]) = 7
Phys. and Anal. Chem. 2015/2016
54
Theory of acids and bases
1) Arhenius theory
Acid: any compound that, when dissolved in water, increases the hydrogen ion
concentration: HNO3 = H+ + NO3Bases: dissociates hydroxyl anion: NaOH = Na+ + OHIt is valid in aqueous medium only; it does not take into account interactions
between a dissolved compound(s) and its respective solvents.
2) Brönsted – Lowry theory – solvation theory
Acid: a proton donor
Base: a proton acceptor
Acid:
HCl (Acid) + H2O (Base) = H3O+(Acid) + Cl-(Base)
Also:
Base:
NH4+(Acid) + H2O (Base) = H3O+(Acid) + NH3 (Base)
NH3 (Base) + H2O (Acid) = NH4+ + OHNH3 (Base) + H+ = NH4+(Acid)
CO32-(Base) + H+ = HCO3-
This theory explains acido-basic reactions in aqueous as well as non-aqueous
medium, e.g., reaction of gaseous hydrochloride and ammonia:
HCl (Acid.) + NH3 (base) = NH4+ (Acid) + Cl- (Base)
It is limited on protic solvents (containing ionizable proton H+)
Phys. and Anal. Chem. 2015/2016
55
Theory of acids and bases II
2) Brönstedt – Lowry theory – cont.
3) Lewis theory
Is valid for compounds, which are not able to dissociate any proton: An Acid is a
compound, which is able to bind free pair(s) of electrons, a base can yield it.
Cl
Cl
Cl
Sn
Cl
+ 2
Cl -
Cl
Sn
Cl
Cl
Cl
Acid
Kyselina
2-
Cl
Cl
Base
Zásada
Lewis acid Lewis Base Adduct of donor-acceptor bond
Phys. and Anal. Chem. 2015/2016
56
Theory of acids and bases III
4) Solvotheory of acid and base (Guttmann – Lidquist – 1954)
Solvoacids: Compounds, which interact with the solvent so, that they increase
the concentration of cataions, produced by autoionization of the solvent.
Solvobases: Compounds, which interact with the solvent so, that they increase
the concentration of anions, produced by autoionization of the solvent.
Protic solvent:
NH3 + NH3 = NH4+ + NH2Acid ionization:
NH4Cl = NH4+ + ClHSO4- + NH3 = NH4+ + SO42Base ionization:
NaNH2 = Na++NH2RNH2 + NH3 = RNH3+ + NH2Neutralization:
NH4+ + NH2- = 2NH3
2 NH4Cl + NaNH2 = NaCl + 2NH3
Aprotic solvent:
SO2(l) + SO2(l) = SO2+ + SO32Acid ionization:
SOCl2 = SO2+ + 2ClPb2+ + 2 SO2 = PbSO3 + SO2Base ionization:
MgSO3 = Mg2+ + SO32Na2O + SO2 = 2Na+ + SO32Neutralization:
SO2+ + SO32- = 2 SO2
SOCl2 + Na2O = 2NaCl + SO2
Phys. and Anal. Chem. 2015/2016
57
Protolytes, protolytic theory
A = H+ + B
Protolytic equilibrium
Acid = Proton + Base
NH4+ = H+ + NH3
Protolytic equilibrium
Acid + Base = Conjugate pair
Phys. and Anal. Chem. 2015/2016
58
Strength of acid I
Strong acid = H+ + weak base
HNO3
NO3-
HCl
Cl-
H3O+
H2O
H3PO4
H2PO4-
CH3COOH
CH3COO-
H2CO3
HCO3-
C6H5OH
C6H5O-
HCO3-
CO32-
HPO42-
PO43-
H2O
OH
NH3
NH2-
Strength
of acid
Affinity
to H+
Strength
of base
Numeric
value of
pKa
Weak acid = H+ + strong base
Phys. and Anal. Chem. 2015/2016
59
Strength of acid II
Dissociation const.
to the 1st oxid. state
HnXOn
HnXOn+1
HnXOn+2
HnXOn+3
10-7
10-2
1
>1
Very weak acids
Weak acids
Strong acids
Very strong
acids
Acid
pK1 (20 oC)
HClO
7.5
H4SiO4
9.7
HBrO
8.7
H3BO3
9.2
HIO
10.6
HClO2
2.0
H2CO3
6.4
H2SeO3
2.64
H3AsO4
2.2
H3PO4
2.2
H5IO6
3.29
HNO2
2.44
H2SO4; H2SeO4
0.4;
HNO3
-1.4
HClO4
HMnO4
-10; -2.3
Phys. and Anal. Chem. 2015/2016
60
Strong acids III
Strongest base
NH3
H2 O
HF
PH3
H2 S
HCl
AsH3
H2Se HBr
SbH3
H2Te HI
Acid
Ki
(pK)
Acid
Ki
(pK)
H3PO4
6·10-3
(2.2)
H2SO4
0.4
(0.4)
H2PO4- 6·10-8
(7.2)
HSO4-
0.01
(2.0)
HPO42- 5.10-13
(12.3)
Strongest acid
Acid
H2O
H2S
H2Se
H2Te
HF
HCl
HBr
HI
H2O2
HClO
K1
10-14
10-7
10-4
10-3
10-3
>1
>1
>1
10-12
10-6
Strongest acid: H2SO4 → CCl3COOH → CHCl2COOH → HNO3 → HCOOH →
C6H5COOH → CH3COOH → H2S → HCN → C6H5OH (phenol) → CH3CONH2
(acetoamide) → C6H5NH2 (aniline) →NH3 : Weakest
Phys. and Anal. Chem. 2015/2016
61
Calculation of pH of weak acids
HA = H+ + A-
Dissociation of acid:
Dissociation constant of an acid:

H 
.A 


KA
H   A 

HA


 
 K A HA  H
 
 log H

 2



KA 
H 
 2
HA
 
K A HA  H

1
1
  log K A  log HA
2
2
1
1
pH  pK A  log HA
2
2
Phys. and Anal. Chem. 2015/2016
62
Hydrolysis of salts
1. Solutions of salts of strong acids and bases are neutral (pH about
7) (influence of CO2 from air)
2. Salts of weak acids or bases react with water – hydrolysis
a) CH3COO- + H2O = CH3COOH + OH- (base)
b) NH4+ + H2O = NH3 + H3O+ (acid)
Examples:
1. Sodium acetate - CH3COONa – aqueous solution is alkalic
2. Ammonium chloride - NH4Cl – aqueous solution is acid
Phys. and Anal. Chem. 2015/2016
63
Calculation of pH of weak acids
1
1
pOH  pK B  log BOH 
2
2
pH = 14- pOH

1
1
pH  14  pK B  log BOH 
2
2
Ampholytes
HB-=B2- + H+
HB- +
H+
= H2B

pH = ½(pKA1 + pKA1) (approx.)
Phys. and Anal. Chem. 2015/2016
64
Titration curve of an acid with strong base
base
 2 pH
0
2
V
Phys. and Anal. Chem. 2015/2016
65
Titration curve of a base with strong acid
 2 pH
0
2
V
acid
Phys. and Anal. Chem. 2015/2016
66
Buffers
In Czech : ústojný, nárazníkový nebo tlumivý roztok
(Germ. Pufferlössung, Franc. Solution tamponné)
A buffer is system composed of two or more compounds,
which decreases the changes of pH caused by the addition
of an acid or an alkali.
e.g., weak acid and its salt (acetic acid + sodium acetate)
Phys. and Anal. Chem. 2015/2016
67
Effectivity in pH range
14
12
10
8
6
4
2
0
Phys. and Anal. Chem. 2015/2016
Davis
Britton-Robinson
NaOH+NaB4O7
NaOH+H3BO3
(Blood)
NaH2PO4+Na2HPO4
Acetic acid+Na acet.
Citric acid + Na citrate
HCl-Glycine
HCl-KCl
Buffers - overview
Components (compositions in tables)
68
Henderson – Hasselbalch equation for
calculation of pH (of simplest) buffers

H 
.A 


KA

HA
Example:


salt 
pH  pK A  log
acid 

salt 
pOH  pK B  log
alkali 
Buffer: CH3COONa – 0.1 mol.l-1;CH3COOH – 0.1 mol.l-1; pKA = 4.76
pH = 4.76 + log([CH3COO-]/[CH3COOH]) =
= 4.76 + log(0.1/0.1) = 4.76 + log(1) =
= 4.76 + 0 = 4.76
Phys. and Anal. Chem. 2015/2016
69
Buffering capacity of some solutions and human blood
blood
Phys. and Anal. Chem. 2015/2016
70
Buffering capacity 
The change of pH caused by addition of small quantity of acid or
alkali:
dc B
c B
c A



dpH pH
pH
Calculation of β: obtained by differentiation of Henderson-Hasselbalch
equation (van Slyke’s equation):
Strong acid + alkali
 
 



K
K
H
H
O
2
A
  2,3.c.
  2,3. H  

1
 H 2

K A  H 


 
 
2
c…total concentration of the buffer (sum of molar concentrations buffer compounds)
KA…dissociation constant (acid part) of buffer system.
Buffering capacity is maximal at pH=pKA.
Buffering capacity increases with increasing buffer concentration.
Phys. and Anal. Chem. 2015/2016
71
(Acetate) Buffer preparation
CH3COOH 0.2 mol.L-1 and CH3COONa 0.2 mol.L-1 (20 oC)
a mL of CH3COOH solution is mixed with (200-a) mL of CH3COONa solution
(27.22 g tri hydrate per liter). pH is changed with temperature neglectable only.
Phys. and Anal. Chem. 2015/2016
72
Thermodynamic laws
Thermodynamic – science dealing with energy transports by
physical and chemical processes
2
Closed system – does not exchange either mass or energy (E = mc )
Open system – exchanges mass and/or energy
vs.
Closed system – does not exchange mass; exchanges energy only
Open system – exchanges mass and/or energy
Isolated system – does not exchange either mass or energy
First Law of Thermodynamics
Sum of all energies in closed system is constant, irrespective of
running physical or chemical processes – work is changed into
energy and energy into work (In a closed system (see below) the
total inflow of energy must equal the total outflow of energy.:
dU = dw + dq (correctly should be , not d, it is not the total
differential)
U - internal energy, w - work, q – heat
Phys. and Anal. Chem. 2015/2016
73
Thermodynamic laws II
Second law of thermodynamic
dQ
dS 
T
Q
S 
T
S…entropy (measure of disorderliness of the system – with increasing
inordinance of the system increases its entropy); Q…heat, T…temperature

The heat cannot spontaneously pass from the colder body to the warmer one.

The entropy of an isolated system is constant or increasing.

It is not possible to construct the periodically working machine, which would
utilize the heat from one accumulator only and which would perform the work
exactly equivalent to this heat.

It is not possible to construct perpetum mobile of the second type.

All spontaneous processes are realized with increasing entropy, with increasing
disorderliness of the system.
Phys. and Anal. Chem. 2015/2016
74
Thermodynamic laws III
Third law of thermodynamic
lim S  0
T 0
Energy types
1. Free energy – „noble“, it can be free transported, transformed
(chemical, electric)
2. Bound energy – heat, which can be transported (flow) only in
the direction of the heat gradient. Transformation to other types
of energy can be realized only, when the warmer body gives its
energy to the colder one.
Phys. and Anal. Chem. 2015/2016
75
Gibbs energy
dG   SdT  VdP  Ad  ...   ~i dni
i
H…
Enthalpy H = U+pV (increase of enthalpy is equal to the heat,
which the system gains under constant pressure, and at the same
time no any other then volume work is produced)
G …
Gibbs energy G = H-TS (= Maximal reversible work other then
volume work, which the system gains (produces) by constant
temperature and pressure
γ …
surface tension
A …
area
~…

electrochemical potential
 G 
~

 i  
 ni  T , P , i ,ni  j
Negatively taken work necessary for releasing of 1 mol of
charged particles and their transport into infinitively diluted state
~  0  RT ln a  zFE
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76
Thermodynamic laws VI - Terminology
Reversible: system is passing through huge amount of small state
changes, by which it is always in equilibrium with surroundings; in
any moment it is possible to stop it and to change the direction of
the process
Irreversible: all changes, which differs from the reversible process
Isobaric: P = const. (pressure)
Isothermic: T = const. (temperature)
Isochoric: V = const. (volume)
Adiabatic: q = const. (heat)
Phys. and Anal. Chem. 2015/2016
77
Exothermic reaction : ΔH < 0
Endothermic reaction : ΔH > 0
Spontaneous reaction: ΔG < 0 (ΔG= ΔH-TΔS)
Unspontaneous reaction: ΔG> 0
Equilibrium ΔG = 0
Thermochemistry
Reaction heat: heat, which the system gains (released), if under
constant pressure the chemical reaction in extension of 1 mol is
realized according to the given equation, provided that the
temperature of the system before the reaction is the same as after
the reaction and that reactants as well as products are in the phase
given in reaction equation.
C(s)+O2(g)=CO2(g)
Phys. and Anal. Chem. 2015/2016
78
Thermochemical laws
First thermochemical law (Lavoisier-LaPlace’s)
The total heat released by the chemical reaction is equal to that one,
consumed by the reversed direction of the reaction.
A ↔B;ΔHA→B = -ΔHB→A
Second thermochemical law (Hess’s)
If a chemical reaction is realized in a few sequential steps, the sum of the
energy, released (consumed) in single steps, is equal to the total energy,
which would be released (consumed), if the reaction would be realized
directly in the only one step.
A→ B → C; ΔHA→C = ΔHA→B + ΔHB→C
It enables to determine the caloric value of foods by their burning up, although in human
body are they metabolized in plenty of gradual steps (glucose, lipids etc.).
Calculation of reaction heat is realized from combination heats (heat, which is released
(consumed) by formation o 1 mol of the compound directly from atoms under constant
pressure and temperature) or from combustion heats (heat, which is released, by
combustion of 1 mol of compound in pure oxygen by formation of most stable oxidizing
Phys. and Anal. Chem. 2015/2016
79
products).
Heat exchange
1. Without any change of the state
T2
H  Q   c p dT   c p (T2 T 1)
i
T1
Q  m.c p (T2  T1 )
T2
c p   C p dT  A  B(T2 T 1) 
T1
C
(T2 T 1) 2
2
2. Latent heat
H Vaporization, Solidification, Liquefaction, Fusion
3. Thermochemical law
Q1  Q2
Heat of fusion = Latent heat of solidification
Latent heat of vaporization = latent heat of condensation
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Heat exchange - 1 kg of water
1. heating from 0 oC to 100 oC
Q  m.c p (T2  T1 )  1* 4.2 *100 kJ  420 kJ
2. Heat of vaporization (normal boiling point)
H Vaporization  2256kJ ~ heating from 0 to 540
oC
3. Melting point (normal fusion point)
H Tání  333.7kJ
Phys. and Anal. Chem. 2015/2016
~ heating from 0 to 80 oC
81
Chemical equilibrium
A B C  D
Reactants A and B; Products C and D
In equilibrium state runs the reaction from the left side to the right
side by the same rate
K
Guldberg-Waage’s law
(1863)

C D

AB
K ... equilibrium constant of the reaction
K ... depends on T, P etc.
In words: The product of molar concentrations of products of the reaction divided by the
product of molar concentrations of reactants is in equilibrium state constant in closed
system.
Le Chatelier's principle
If a chemical system at equilibrium experiences a change in concentration, temperature,
volume, or partial pressure, then the equilibrium shifts to counter-act the imposed change.
Phys. and Anal. Chem. 2015/2016
82
Chemical equilibrium II
[C].[D] = [B].[A]=> K=1
[C].[D] > [B].[A] => K>1 – prevailing products
[C].[D] < [B].[A] => K<1 –prevailing reactants
Oscillating reactions: e.g., Zhabotinsky
To influence the course of the reversible reaction (its direction), it
is necessary to work in open system.
If one component of the reaction is removed, the system produces
the removed amount continuously to reach (restore) the
equilibrium. Thereby we can reach practically total realization of
the reaction in the direction, in which it practically does not run in
closed system (K<<1).
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Possibilities of influencing of steady state (equilibrium)

C D
1. Decrease of final products quantity
K 
2. Increase of starting compounds quantity
AB
3. By inequal number of molls of starting compounds and final product
in gaseous system (2A + B = C) the change of pressure
4. Change of temperature (exothermic – the rate decreases with
increasing temperature; endothermic – the rate increases with
increasing temperature)
All reactions in living systems are realized in open systems,
consequential, consecutive reaction takes off products of previous
reaction, whereby the equilibrium (steady) state is disturbed and so
influences the course of the reaction.
A+B=C+D → D+E=F+G → G+H=I+J → J+K=L+M
The compound M is as the final product of the metabolism removed from
the (living) system away, e.g., by respiration or excretion.
Catalyzers influence the reaction rate, but not the equilibrium. They are
enabling other reaction way, energetic of the reaction, but not the
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equilibrium!!!
Reaction rate, order of chemical reaction
d [ A] d [C ]

v 

 k C 
dt
dt
AC
A B  C  D
 
v  k C D 


 v K  k  C D
k AB 
 
v  k  AB 
Equilibrium:
1st order reaction
2nd order reaction

v
 
v  k  A
AC  D
  2
v  k  A
2A  C  D
 
v  k  AB  A  B  C  D
Reaction of more than 2nd order is realized in fact stepwise,
gradually, as the reaction composed of more reaction substeps. For the reaction rate is the controlling the slowest one).
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Reaction rate, order of chemical reaction
1st order reaction
 
v  k A v   d [ A]  k[ A]
dt


 kt
ln[ A]  k t  ln[ A0 ] [ A]  [ A0 ]e


A0=1 mol.L-1
0.9
ln( 2)
k
Concentration [mol.L-1]
zero order
reaction
t1/ 2 

[C]  [C0 ] 1  ekt
1.0
Reaction half-life
AC
[ A]  [ A0 ]  kt
0.8
0.7
-1
k=1 L. mol .s
0.6
-1
0.5
0.4
-1
k=1 s
0.3
Zero order
0.2
First order
0.1
Second order
k=1 mol.L-1.s-1
0.0
0.0
2nd order
reaction
0.2
0.4
0.6
0.8
1.0
t [s]
d [ A]
  2
v  k A  
dt

1
1

 kt
A A0 
2
2A  C  D
2 NO2 → 2 NO + O2
A  A0 
A0 k t  1
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t1/ 2
1

k  A0 
86
Influence of the Temperature on the Reaction Rate
Increase of the temperature increases the reaction rate. Their
relationship is given by Arhenius equation:
 E

k  A. exp 

a
RT 
k... rate constant, A… function factor; T … absolute temperature; Ea…
activation energy; R universal gas constant
It follows that the increase of the
temperature essentially increases
the reaction rate – exponentially.
activity
This fact is commonly used by
homonotermn organisms, e.g., by
defense reactions, such reactions
run at higher temperature faster and
they are more effective.
Coeffitient Q10 = how many times changes the reaction rate by
the change of the temperature by 10 grades ~ 2
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Catalysis
For many catalyzed (enzymatic) reactions is valid:
Catalysts: A compound
products
influencing
the reaction rate of the chemical
reaction, but it does not take part in
the reaction; it changes the reaction
mechanism, it changes the
activation energy, it is involved in
the formation of the activation
complex: A+B→AB vs.
A+B+K→ABK→AB+K
Catalysts:
Catalysts:
a) positive
a) homogeneous
b) negative (inhibitors)
b) heterogeneous
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Sorting of chemical reactions
• Inorganic: synthetic, analytical, substitution, double replacement
• Organic: Additions, eliminations, substitutions, rearrangements
According to the character process: Redox (transfer of
electron), acidobasic (protolytic – transfer of proton),
coordination (complexing)
According to the number of phases: occurring during the reaction
a) Homogenous: reactants and products are in one phase:
H2SO4 (l) +NaOH (l)= Na2SO4 (l) +H2O (l)
b) Heterogeneous: reactants and products in more phases
2HI(g) =(Pt-catalyzer)= H2 (g) +I2 (g)
(catalysis of the reaction in gaseous phase on the solid catalyzer)
H2O(l) + CO2(g) = H2CO3(l)
c) Ionic reaction: Only ions take part in the reaction – character of the
ionic reaction could be redox, acido-basic, coordination,...
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Oxidation - reduction reactions (redox)
Reactions, in which is realized the transport or the redistribution
of electrons among reactants.
Lose of electron = oxidation (Pb  Pb2+ + 2e-)
Receiving of electron = reduction (Pb2+ + 2e-  Pb)
Reduction = Receiving of hydrogen (cystine  cysteine);
Oxidation = Lose of hydrogen (cysteine  cystine)
When one reactant (atom) is oxidized, the other reactant must be reduced.
Similarly as in case of protolytic reactions, one reactant is in oxidized form and
the other one in reduced form (redox system) and the equilibrium is established
between both forms.
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Electric doublelayer
Electrode
Electrode
Solution
Diffusion part
Helmholtz part
Use:
a) Electrolysis of the solutions
b) Electroplating
c) Tooth cell – improper materials
d) Voltammetry
e) Power sources
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Oxidation - reduction reactions (redox)
Example
Galvanic cell - spontaneous
Anode: Zn=Zn2++2e1st redox system E0(Zn2+/Zn)=-0.76 V
Cathode: Cu2++2e-=Cu
2nd redox system E0(Cu2+/Cu)=0.34 V
Zn(s) + Cu2+ = Cu(s) + Zn2+ U=Ec-Ea
Measurement of redox potential (Secondary school)
Electrolytic cell – Inserted voltage
Anode: Cu = Cu2+ + 2e1st redox system
Cathode: Zn2+ + 2e- = Zn
2nd redox system
Cu(s) + Zn2+ = Zn(s) + Cu2+ U=Ea-Ec
Reduction is always realized at cathode!
E1  E10 
a
a
RT
RT
RT a1red
ln
U  E1  E 2  E10 - E 02 
ln 1red 
ln 2red
nF a1ox
nF
a1ox
nF
a 2ox
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Oxidation - reduction reactions (redox)
Redox pair
[V]
Redox pair
[V]
Li+/Li (s)
- 3.04
Co2+/Co (s)
- 0.28
K+/K (s)
-2.92
Ni2+/Ni (s)
- 0.25
Na+/Na (s)
- 2.71
Sn2+/Sn (s)
- 0.14
Ca2+/Ca (s)
-2.50
Pb2+/Pb (s)
- 0.13
Al3+/Al (s)
- 1.66
2H+/H2 (g)
+0.00
Mn2+/Mn (s)
- 1.18
Sn4+/Sn2+
+0.15
Zn2+/Zn (s)
- 0.76
Cu2+/Cu (s)
+0.34
Cr3+/Cr (s)
- 0.74
Ag+/Ag (s)
+0.80
Fe2+/Fe (s)
- 0.44
Cl2/2Cl-(g)
+1.36
Cd2+/Cd (s)
- 0.40
Au+/Au (s)
+1.50
Tl+/Tl (s)
- 0.34
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Oxidation - reduction reactions (redox) I
Standard electrode potentials at 25 oC in aqueous solutions
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Oxidation - reduction reactions (redox) II
The redox pair with the higher standard potential is the
oxidant of the redox pair with the lower standard potential.
Voltage change:
1. Connection of two different metals
2. Connection of the same metals dipped in two different
electrolytes (different concentration)
Electric current direction
a) Galvanic cell b) electrolytic cell
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Oxidation - reduction reactions (redox) III
Comparison of efficiency of energy production by microorganisms. In
parentheses are numbers corresponding to ΔGO’ in kJ.mol-3, cytFe3+ and cytFe2+
are oxidized and reduced forms of cytochroms
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Redox reactions in living organism
Living organisms commonly use redox reactions as energy
sources. A number of organic compounds exist in oxidized form as
well as in reduced form and therefore they can be involved in the
transport of electrons. In these processes the organisms gain the
energy necessary for life. Transferred electrons enable, e.g., transport
of protons (H+) through membranes and enable the changes of pH.
Accumulated protons by reverse transport through the membrane can
supply the energy for the transport of other compounds or for the
synthesis of ATP.
From redox potential of two equal redox systems we can
calculate ΔGo of the chemical reaction ΔGo = -zF ΔE’o (z – number
of transported electrons) by the change of the redox potential ΔE’o
(ΔE’o - „biologic“ standard reduction potential – standard system
state for pH=7) [Ared]=[Aox].
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Redox reactions in living organism II
During the aerobe transformation of compounds (metabolism) is
realized (in principle) strong exergonic reaction (and exothermic)
redox reaction: 2H2+O2→2H2O. The high energetic electrons of
hydrogen are transported on oxygen in many sequential steps. Their
energy is used for living processes of the cell (organism). These
processes are studied in biochemistry. As electron carrier are often
used metals bound on peptides.
Spontaneous reaction = exergonic (exothermic)
Non-spontaneous reaction = endergonic (endothermic)
2H2(g)+O2(g)→2H2O(g) ΔGo =-242 kJ.mol-1 – exothermic (burning)
2H2O(g) → 2H2(g)+O2(g) ΔGo =242 kJ.mol-1 – endothermic,
equilibrium is shifted to the left, only by high temperature and
decreased pressure starts the decomposition (at 2100 oC and 0.1 MPa
reacts 2 % of molecules only) .
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Analytical methods
1. Phase separation methods (chromatography);
2. Electrochemical methods (polarography, voltammetry,
electrophoresis, izotachophoresis, potentiometry);
3. Spectroscopy (AAS, AES, UV/VIS spectroscopy);
4. Mass spectroscopy;
5. Optical (Polarimetry);
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Chromatography
Principle: widely used method of chemical analysis based on
physical-chemical separation of gaseous mixtures of
compounds (gas chromatography) or of liquid solutions (liquid
chromatography) between two phases (stationary and mobile).
All chromatographic methods are based on gradual, repeatedly
established equilibriums of separated compounds between two
phases. It is used by the analysis of complicated mixtures of
compounds.
Realization:
Column (CC)
Thin layer (PC, TLC)
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Chromatography II
•
•
Mobile phase:
gaseous (GC)
liquid (LC)
Stationary phase:
solid phase, which differs from the
mobile phase – it enables separation
between mobile and stationary
phases.
 Liquid (LC)
 Solid (SC)
Carrier: used for anchorage of the solid phase
(glass bead: Silica Gel – silanic bond –Si-O-SiOH + C18H37Cl = HCl + C18H37-O-Si – non-polar)
Capillaries: stainless steel, plastics, glass, quartz, …
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Chromatography III
Stationary phase:
1. Hydrophilic compound: (silica gel, dextran), cellulose
(paper), less often hydrophobic compound
2. Molecular sieve: (beads from a cross-linked polymer), small
molecules are caught on the sieve, larger pass around beads
3. Ion exchanger: on solid phase are bound the groups with
positive or negative charge. These attract the opposite
charged compounds, and decelerate their transport.
a) NPC – normal phase (mobile phase is non-polar,
stationary is polar)
b) RPC – reversed phase (mobile is polar, stationary nonpolar)
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Types of chromatography according to the separation principle:
1.
2.
3.
4.
5.
Separation – the compounds are separated according to their different solubility
between stationary phase (liquid is bound on the surface of powdered porous or other
carriers) and mobile phase (liquid, gas)
Adsorptive – adsorption from liquid or gaseous mobile phase on stationary phase
with large surface
Affinitive - the compounds are separated according to heir different affinity to the
groups bound to the stationary phase
a) Ionex (ion exchanger) – on the solid carrier are bound acid or basic groups,
which are able to bond opposite charged compounds (ions). If the ionex bonds
anions, we call them anion exchanger, if it bonds cations, we call it cation
exchanger. The fixed ions can be exchanged for weaker bounded ions (ion
exchangers)
b) Other: Immuno-affinitive (Ag-Ab), enzyme – substrate, lectins etc.
Electrophoresis – chromatography with inserted potential field
Gel (molecular sieves – sephadex, polydextran) – the smaller molecules are caught
inside the molecular sieves and their passage is slower. Larger particles are not
caught and they are passing faster. GPC (Gel Permeation Chromatography).
Attention, the smallest particles go inside the bead, but their are trapped there so
strong that they cannot be washed out by the mobile phase. On the contrary, the
largest are not caught at all, they are passing directly.
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Chromatography – international nomenclature
(abbreviations):
Names of methods are derived from international names of phases
L-liquid, G – gas, S – solid) and the word „chromatography“ (C)
1.
LSC – Liquid – Solid chromatography – liquid chromatography with solid
embedded stationary phases (adsorptive)
2.
GSC – Gas – Solid chromatography – gas chromatography with solid
stationary phase (adsorptive)
3.
LLC – Liquid – Liquid chromatography – liquid chromatography with liquid
stationary phase (absorptive) on solid carrier
4.
GLC – Gas – Liquid chromatography – gas chromatography with liquid
stationary phase (absorptive) on solid carrier
The liquid chromatography (LLC, LSC) with high pressure is very frequently used
at present. It substantially increases rate and efficiency of the analysis. Its
abbreviation is derived from:
HPLC – High Performance Liquid Chromatography
HPLC and gas chromatographs are the fundamental equipments of each laboratory,
dealing with toxicology, bioanalysis and analysis of pharmaceuticals.
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The application range of various types of
chromatography according to the separation principle:
Molecular weight
1000000
100000
10000
1000
100
10
1
GPC
PC+TLC
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HPLC
GC
105
Detectors in chromatography
Detectors
Principles
1. Differential
1. Flame-ionization;
2. Integral
2. Conductive;
3. Electron capture;
4. Amperometric;
5. Optic;
6. UV/VIS;
7. MS – mass spectroscopy.
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MS – mass spectroscopy
Method using electric and magnetic field for the separation of ions
according to their mass and charge. It is possible to obtain qualitative
as well as quantitative information on analyzed compound.
2
2
a) By electrons
m B r
m

  r2
z
2V
z
b) Chemically
m … ion mass
c) By electric field
z … ion charge
1. Ionization
2. Identification of
formed ions
B … magnetic induction
r ... radius
V … voltage
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Electroanalysis
Methods of chemical analysis, using for the analysis of the effects
connected either with transport of electric charge between the
analyzed probe and the electrode (e.g., potentiometry) or with
transport of charged particles in the compound between electrodes
(e.g., coulometry, conductometry, polarography, voltammetry).
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Potentiometry
a) Method of electroanalysis, used for the determination of
compounds by measurement of electromotoric voltage of
galvanic cell between indication electrode (dipped into analyzed
solution) and reference electrode (with constant potential) (e.g.,
concentration of H+ or F- ions using Ion selective electrode)
b) Determination of point of equivalence (s.c., potenciometric
titration).
ion selective electrode (ISE), its potential is given by s.c., membrane
potential (it is established on the membrane with limited permeability for
some ions). The potential of ISE is proportional to the concentration(s) of
some ion(s) in the solution. They are often used in analytical praxis (e.g.,
Ag-ISE, F-ISE).
Glass electrode, the oldest ISE with semi-permeable membrane
(permeable for H+ (H3O+) ions) made from thin-walled glass. Most
frequently used for the determination of pH of solutions.
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Coulometry, conductometry, polarography (voltammetry)
Coulometry
Determination of the quantity of the compound on the basis of
transported charge (Coulomb’s law):
n
Q
i.t
i.t

m
zF zF
MzF
Conductometry
Determination of amount or concentration or composition of the
compound between the electrodes on the basis of the conductivity.
Polarography
Measurement of the dependence of direct electric current on the inserted
voltage by the passage through analyzed system, using polarizable drooping
(mercury) electrode and non-polarizable electrode (reference). The half-wave
potential (it is obtained from recorded curves (waves) is given by the quality
(composition) of the system; the height of the peak (wave) is proportional to
the quantity of the compound. Discoverer of polarography was Prof.
Jaroslav Heyrovský – 1st polarographic curve December 1922
First Nobel price in ČSR 1959.
Voltammetry – the same as polarography, only the hanging mercury drop
electrode or some solid electrode are used (the signal has the shape of a peak
– not a wave!)
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Electrophoresis
Separation method based on different mobility of charged particles in
the same phase. Electrokinetic phenomenon is process, in which the
particles of dispersed solid phase are in liquid dispersive medium
transported in electric field to the opposite charged electrode (in
comparison with the charge on their surface). The transport rate of the
particles is direct proportional to the intensity of the electric field and to
the electrokinetic potential and inversely proportional to the viscosity of
the solution. Electrophoresis is frequently used in biochemistry (e.g.,
separation of peptides) and in other organic technologies.
According to the mediums, in which is the electrophoresis realized:
a) free electrophoresis in aqueous solution, Tiseli electrophoresis;
b) zonal electrophoresis on inert carriers (filtration paper, Silica Gel,
synthetic gels);
c) Column – in combination with chromatography.
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Spectral methods of chemical analysis
Spectroscopy originally visual observation of optical spectrum. Today branch
of physics, dealing with origin and properties of spectra (optical, X-ray,
electronic, mass), and their relation to inner structure of compounds.
Spectroscopy brings valuable information for physics, chemistry and other
technical sciences (AAS, AES, ICP, IR, UV/VIS).
Optical emission and absorption spectrometry, spectral analysis
Collection of methods, using the knowledge of spectroscopy for purposes of
chemical analysis. Spectral methods of qualitative chemical analysis ascribe spectral
lines to elements, quantitative determine the intensity of particular lines; absorption
methods determine the amount of absorbed energy (from the power source).
Electron spectroscopy: study of interactions of electrons or photons with analyzed
material, determination of kinetic energy of secondary electrons, emitted by
interactions. There are a few types of this spectroscopy (according to the primary
power source and secondary released electrons): e.g., ultraviolet photoelectron
spectroscopy, electron spectroscopy for chemical analysis ESCA. The methods of
electron spectroscopy are used for analysis of surfaces of solid materials. For
chemical analysis is relatively most important ESCA.
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