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DISPERSED SYSTEMS
Ingrid Žitňanová
DISPERSED SYSTEMS
Dispersed
phase
(water)Dispersionmedium
(oil)
SOLUTE
(DISPERSED PHASE )
SOLVENT
(DISPERSION MEDIUM )
Solute (NaCl) Solvent (water)
Heterogeneous and Homogeneous Mixtures
Dispersed
systems
Heterogenous
systemsHomogenous
systems
e.g. sugar watere.g. ice in soda
Homogenous Heterogenous
It has a uniform composition It has a non-uniform composition
It has only one phase There are two or more phases
It can’t be separated out physically It can be separated out physically
Examples: sugar water, vinigar,
NaCl in water....
blood, sand in water, ice in soda,
cereal in milk, vegetable soup...
Difference between Homogenous and
Heterogenous dispersions
Classification of the dispersed systems
according to the diameter of dispersed particles
1. Analytical (molecular, true solutions)
2. Colloids
3. Coarse / Crude dispersion (suspension)
< 1 nm
1 – 1000 nm
>1000 nm
SolutionColloidsSolution Coarse dispersion
particle sizeType of dispersion
Properties of the dispersed systems
Dispersion Molecular (true solut.) Colloidal Coarse (crude)
Particles size 1 nm 1 – 1000 nm > 1000 nm (1 μm)
Particles Filterability Cannot be separated by
filtration
Can be separated by
semipermeabile
membrane
Can be separated by
filtration
Diffusion rapid slow No diffusion
Visibility Not visible under the
electrone microscope
Can be visible under
the electrone
microscope
Can be seen under
the low power
microscope or eye
Sedimentation Particals do not sediment Sediment in the
strong centrifugal
field
Sediment under the
influence of gravity
Optical properties Transparent
No Tyndall effect
Tyndall effect Not transparent
Tyndall´s effect
is due to the scattering of light by colloidal particles, while showing
no light in a true solution.
This effect is used to determine whether a mixture is a true solution
or a colloid.
True
solution
Colloidal
solution
• when light is passed
through a colloidal
solution, the substance
in the dispersed phases
scatters the light in all
directions, making it
readily seen
TRUE SOLUTIONS
(Analytical solutions)
SolventsPolar
Nonpolar
Solutes
Polar
Nonpolar
• Polar solutes dissolve well in polar solvents
• Nonpolar solutes dissolve well in non-polar solvents
• Polar and nonpolar do not mix...
– e.g.water, ethanol, methanol,
– e.g. chloroform, hexane, benzene
- ethanol, acetic acid, NaCl
- fats, steroids, waxes
Oil in water
Water
The most important polar solvent
Intracellular fluid ICF – inside cells – 25 - 30L
Extracellular fluid ECF – 15L - blood plasma, intersticial fluid,
lymph, fluid in gastrointestinal tract, urine
Volume of water in body is balanced (intake = output)
Central regulatory organ of water volume – kidneys
Hydrogen
bond
Water – H2O – a polar solvent
O
O
O
O
HH
H
H
H
H
H
H
True solutions
Ionic Molecular
• Solutions of nonelectrolytes
• Contain molecules of compounds in
solution (glucose in water, urea)
• solution of electrolytes in which ions
are present, formed by electrolytic
dissociation of ionic compounds
Na+
Cl-H2OH2O
Cl-
Cl-
Cl-Cl-
Cl-
H2O
NaCl Na+ + Cl-
Electrolytic
dissociation
Hydrated
ions
Ionic strength ( I )
is the concentration of ions in the solution
i – number of particles
ci - the molar concentration of particles (ions)
zi – charge of the particle
Only ionized species contribute to ionic strength in
solution!!!
• Ionic strength of blood is around 0.17 mol/L
Example 1:
Calculate ionic strength of a solution containing 0.02 mol/L
Na2SO4 and 0.1 mol/L glucose.
I1 = 0.5 [(2 x 0.02 × 12 ) + (1 x 0.02 × 22 )] = 0.06 mol/L
1. Na2SO4 = 2Na+ + SO42-
2. Glucose0 no dissociation
I2 = 0.5 x 1 x 0.1 x 02 = 0 mol/L
I = I1 + I2 = 0.06 + 0 = 0.06 mol/L
SO42-2Na+
Solubility
A measure of how much of a solute can be dissolved in a solvent
Factors affecting solubility
• Temperature
• Pressure
• Polarity
Temperature
For most solids and most liquids
Solubility increases when solution temperature increases
Temperature
For gases
Higher temperature reduces solubility of gases –
it drives gases out of solution
Examples:
Carbonated soft drinks are more bubbly if stored in the
refrigerator (more CO2 is inside the drink)
Warm lakes have less O2 dissolved in them than cool
lakes
Pressure
• Little effect on solids and liquids
• Will greatly increase solubility of gases
Polar substances tend to dissolve in polar solvents.
Nonpolar substances tend to dissolve in nonpolar solvents.
Examples
Polarity
Vitamin A is soluble in nonpolar compounds (e.g. fats)
Vitamin C is soluble in water
Vitamin A Vitamin C
Properties of true solutions
Colligative properties don´t depend on the chemical composition of a
solute, but depend only on the number of solute particles (molecules or
ions).
The processes based on colligative properties are:
• Diffusion
• Dialysis
• Osmosis
• Boiling point elevation
• Freezing point depression
Diffusion
is a process of spontaneous movement of particles of a dissolved
compound from a region of higher concentration to a region of lower
concentration, to distribute themselves uniformly = movement of a
substance down a concentration gradient
The rate of diffusion depends on the concentration gradient
Particles move until equilibrium is reached
Diffusion usually happens in a solution in gas or in a liquid.
Examples of diffusion:
A sugar cube is left in a beaker of water for a while.
The smell of food spread in the whole house
Dialysis
Concentrated
sugar solutionDiluted
sugar solution
Movement of low
molecular weight solute to
equal concentrations
Water and low molecular weight LMW compounds (not macromolecules)
are transported across a semipermeable membrane. LMW compounds go from
the more concentrated solution to the less concentrated solution till equilibrium
is reached. Semipermeable membrane
Biomedical importance of dialysis
Dialysis by artificial kidney: In patients with acute kidney injury and
uremia blood is dialyzed in artificial kidneys to eliminate waste products.
Hemodialysis - Blood dialysis
- removal of waste metabolic products (e.g. urea
or creatinine) or toxins, by kidneys
Dialyzing
membrane
Dialysate
- solution isotonic with blood,
- it has the same concentrations of all the
essential substances that should be left in blood
Dialysate
Filtered blood
returning to
bodyBlood flows to
dialyzer
Hemodialyzer
machine
Hemodialyzer
(where filtering takes place)
Osmosis
Osmosis is the flow of solvent across a semipermeable membrane
from a lower solute concentration to a higher solute concentration
semipermeable membrane is permeable only to solvent molecules,
not to solute molecules
Concentrated
solution
Diluted
solution
Semi-permeable
membrane
Osmotic pressure (π)
- external pressure that has to be applied on the more
concentrated solution to stop osmosis
i – number of solute particles in solution to which the compound dissociates
c – amount of substance concentration (mol/L)
R – gas constant – 8.314 J K-1 mol-1
T – temperature in Kelvins (0 °C = -273.15 K)
π = i.c.R.T
π of blood - 780 kPa
π
Movement of solvent (water)
to equal concentrations
Osmolarity (cosm)
molar concentration of all osmotically active particles of solutes in
solution
cosm = i . c
cosm - osmolarity mol/L
i – number of solute particles in solution to which the
compound dissociates
c – amount of substance concentration (mol/L)
Osmolarity (cosm)
Blood serum osmolarity:
πblood = i . c . R . T
cosm
πblood 780 kPa
Blood cosm = = = 0.3 mol/L R . T 8.3 JK-1mol-1 . 310 K
• Osmolarity is kept constant by kidneys
Example 1:
Calculate osmolarity of the solution containing 0.2 mol/L CaCl2
and 0.1 mol/L glucose.
1. CaCl2 = Ca2+ + 2Cl-
2. Glucose no dissociation
cosm = i1 . c1 + i2 . c2
cosm = 3 x 0.2 + 1 x 0.1 = 0.7 mol/L
i1 = 1Ca2+ + 2Cl
- = 3
i2 = 1glucose
Isotonic /isoosmotic solutions
Isotonic solutions are two solutions that have the same
osmolarity.
Hypertonic solution
Hypertonic solution is one of two solutions that has a higher
osmolarity.
Hypotonic solution
Hypotonic solution is one of two solutions that has a lower
osmolarity.
Solution of NaCl with concentration of 0.15 mol/L
Solution of NaCl with osmolarity of 0.3 mol/L
0.9% NaCl solution (9 g NaCl/L)
Physiological solution
Solution which osmotic pressure corresponds to blood plasma:
Any solution added in large quantity into the bloodstream has
to be isotonic!!
hemolysis
Crenation
Cells shrink
Oncotic pressure
Oncotic pressure, or colloid osmotic pressure, is a form
of osmotic pressure exerted by proteins (e.g. albumin) in a blood
that usually tends to pull water into the circulatory system.
Water flow driven by
oncotic pressure
diference
Capilary
lumen
Small molecules and ions can be dialyzed in both directions between
blood and the interstitial compartment
Large protein molecules do not have this ability – their presence
produces excess osmotic pressure of blood (oncotic pressure)
compared to the interstitial fluid.
The hydrostatic pressure of a blood tends to push water out of the
capillary – filtration.
The oncotic pressure pulls the water from the interstitial space back
into the capillary – reabsorption.
Exchange of compounds
between blood and tissues
Donnan equilibrium
High molecular weight
compound
semi-permeable membrane
equilibrium
• According to Donnan´s equilibirium, the products of diffusible electrolytes in
both comparments will be equal
• in the left compartment: Na+ x Cl- = Na+ x Cl- in the right compartment
• in the left compartment: 9 x 4 = 6 x 6 in the right compartment
4Na+, 4Cl-
refers to the uneven distribution of charged particles on one side of a
semipermeable membrane
Donnan equilibrium
equilibrium
1. The products of diffusible electrolytes in both compartments are equal (9x4=6x6)
2. The electrical neutrality of each compartment is maintained (9 + and 9 - in the left)
3. The total number of a particular type of ions before and after the equilibrium is
the same (15 Na+ before, 15 Na+ in the equilibrium)
4. When there is a nondiffusible anion on one side of a membrane, there are
more diffusible cations and less diffusible anions on that side
In summary, Donnan´s equations lead to the following results:
Colloidal dispersions
Colloidal dispersion
is a mixture consisting of large clusters of ions or molecules, or
macromolecules with size of particles 1 – 1000 nm
the dispersed particles do not settle down
particles can be visible under the electrone microscope
particles diffuse slowly
show some unique properties such as Tyndall effect, Brownian
motion
almost all reactions in the organism proceed in colloid
environment
True
solution
Colloid
High–molecular weight (macromolecular) compounds (e.g. proteins,
polysaccharides), in process of dissolution spontaneously form
colloidal solutions
Low–molecular weight compounds may form colloidal solutions as
a consequence of clustering of molecules into aggregates – micelles
(e.g. soap solutions).
Classification of colloids
1. Based on physical state of dispersed phase and
dispersion medium
Sols
Gels
Emulsions
Aerosols
Sols
If the dispersion medium is water, the colloid may be
called a hydrosol; and if air, an aerosol.
Are colloidal solutions made of globular proteins with
normal viscosity
Particles in colloids are isolated
Gels
.
they arise by swelling macromolecular compounds (e.g.proteins) in
solvent – acceptation of water by solid polymers
are formed from fibrous proteins (gelatin from collagen), polysaccharides
(gels – dextran, sephadex).
The wall of the living cells is colloidal, and within the cell there is
a gel (cytoplasm).
Gels undergo aging - particles coagulate, gel volume diminishes and
water is displaced
Protein
moleculesdispersed in
water
waterwater
Protein
molecules
Mechanical
shaking
When particles in colloids are isolated – sol. When they form clusters–gel.
Emulsions
are colloidal dispersions of two immiscible liquids (e.g. oil in water, or
water in oil) when are shaken together.
usually are not stable (e.g. the oil soon separates from the aqueous layer).
can be stabilized by a third component called emulsifying agent
(emulsifiers) (soaps, fats...).
Biologically important emulsions:
lipids in blood – emulsified by proteins
fat emulsions in intestine – emulsified by salts of bile acids
Colloids
LyophilicLyophobic
Micelles
2. Classification of colloids according to their
properties
Macromolecular
compounds Low-molecular
weight compounds
Low-molecular
weight amphipatic
compounds (soaps)
1. Lyophilic colloids
• Solvent attracting, solvent loving particles
• If water is the solvent (dispersing medium), it is known as a
hydrosol or hydrophilic colloids
• particles of a lyophilic colloid are stabilized in solution
(prevention of aggregation) by solvation (hydration) shell, i.e.
oriented solvent molecules
• are formed by spontaneous dissolving of macromolecular substances
(e.g. solutions of proteins, starch...)
1. Lyophilic colloids
The loss of hydration shell after excess of neutral salt (electrolyte) is
added into solution results in irreversible salting out (precipitation)
of particles from solution.
The living cells represent solutions of lyophilic colloids
(as well as coarse dispersions)
• solvent hating colloids, have no affinity for the dispersion medium
2. Lyophobic colloids
• unstable colloid systems in which the dispersed particles:
- tend to repel liquids,
- are easily precipitated
• require protective colloids (lyophilic colloids – gums, gelatin...) to
stabilize in water
Lyophobic soll particle
(particle being protected)
Lyophilic colloidal particle
(protecting particle)
Explanation: The particles of the hydrophobic sol adsorb the particles
of the lyophilic particles. The hydrophobic colloid, therefore, behaves
as a hydrophilic sol and is precipitated less easily by electrolytes.
2. Lyophobic colloids
• are made artificially by aggregation of low molecular weight substances
• Examples: sols of metals and their insoluble compounds like sulphides and
oxides (e.g. gold, silver, platinum in water, cluster of inorganic molecules,
e.g. As2S3)
• Therapy: colloidal systems are used as therapeutic agents in different areas
Silver colloid – germicidal effects
Copper colloid – anticancer effects
Mercury colloid - antisyphilis
Colloidal goldColloidal silver
3. Association colloids – micelles
are formed by dissolving of low-molecular weight amphipathic compounds
Amphipathic compounds contain both polar (hydrophilic) and nonpolar
hydrophobic regions (e.g. fatty acids)
Polar part
Nonpolar part
when mixed with water, amphipatic compounds form colloidal particles –
micelles (e.g. soap, detergents)
Soaps
consist of sodium or potassium salts of higher carboxylic acids
Soaps
Polar -Lyophilic part
lyophilic end of the COO- dips in water, while the lyophobic part stays
away from it
When soap is shaken with water it forms a colloidal dispersion which
contains aggregates of soap molecules - micelles
Nonpolar - Lyophobic part
Dirty cloth
Dirt
Soap molecules
Soap solution
Mechanism of soap action
• The hydrophilic heads (with – charge COO-) interact with water
and the oil drop is stabilized in water.
• The hydrophobic ends attach themselves to the dirt and remove it
from the cloth
Biological importance of colloids
Biological compounds as colloidal particles: the complex molecules of life,
the high-molecular weight proteins, complex lipids and polysaccharides
Blood coagulation: when blood clotting occurs, the sol is converted finally
into the gel.
Biological fluids as colloids: these include blood, milk and cerebrospinal
fluid, lymph, mucus, cytosol, nucleus, cell membranes
Colloidal state is one of the most widespread in nature:
Reaction kinetics
Chemical reaction
Reaction means a change
Chemical reaction is a conversion of reactants to products
A + B C + DReactants Products
Reagents
Reaction kinetics
Kinetics of a chemical reaction can tell us:
How chemicals react to form products (mechanism)
How long it will take for a reaction to reach completion
Effects of catalysts and enzymes
How to control a reaction
A + B C
Rate equation(Guldberg Waage rate law)
The rate of a given chemical reaction (at constant temperature and
pressure) is proportional to product of reactants concentration.
For the general reaction:
aA + bB cC
Rate: v = k . [A]a . [B] b
k = rate constant
[A], [B]= molar concentrations of reactants (mol/L)
Rate constant
k = rate constant
A = Arrhenius constant for each chemical reaction (total number of collisions)
Ea = activation energy
R = gas constant (8.314 J K-1 mol-1)
T = Temperature in Kelvins
e = euler number (2.71828...)
Temperature has a dramatic effect on reaction rate.
For many reactions, an increase of 10°C will double the rate.
Higher T larger k increased rate
Reactant Product
aA bB
When concentration of products and reactants no longer change with time,
the chemical reaction reached equilibrium
equilibrium
Effective collisions
For reactants to make products
They must collide in the correct orientation and with sufficient energy
The energy of collision must be greater than the bond energy
between the atoms
Molecules must collide with the correct orientation and with
enough energy to cause bond breakage and a new bondformation
Activation energy
The minimum amount of energy required to start a chemical reaction
Activation energy
Transition state
(activated complex)
Activation energy
Reactants
Products
Factors which affect the rate of chemical
reactions
Rate of
reaction
The nature of
reactants
Temperature
Concentration
of reactants
Catalysts
Natu
reo
fre
act
an
tsNumber of bonds
• fewer bonds per reactant - faster reaction
Strength of bonds• Breaking of weaker bonds - a faster rate (-C-C- / -C=C-)
The size and shape of a molecule• Complicated molecules or complex ions are often less reactive
Less particles, less frequent
and successful collision
More particles, more frequent
and successful collision
Concentration of reactants
As the concentration of reactants increases, so does the likelihood that reactant
molecules will collide - the reaction rate will increase
Temperature
An increase of about 10°C will often double the rate of a reaction
Catalysts
Catalysts speed up reactions by changing the mechanism of the reaction – they
reduce activation energy of reaction
Catalysts are not consumed during the reaction
Oxidation – reduction reactions
(redox reactions)
Oxidation – reduction reactions
(redox reactions)
Oxidation is the loss of electrons (or hydrogen), the species which loses
the electrons is oxidized, it becomes more positive
Reduction is the gain of electrons (hydrogen), the species which gains
electrons is reduced, becomes less positive.
Na0 → Na+ + 1e-
Cl20 + 2e- → 2Cl-
Oxidation and reduction reactions occur simultaneously
chemical reactions where one of the reactants is oxidized and one of the
reactants is reduced
Decide, in which direction the following reaction is an oxidation and
in which it is a reduction
Oxidation – reduction reactions
(redox reactions)
- electrons are exchanged between chemical species
Na Cl
+ -
-
Na Cl
In these reactions there are changes in the valence shells of atoms
+ -
Oxidizing agent – oxidant - is the chemical species causing the
oxidation. This species is reduced and can also be called the
electron acceptor.
2Na0 + Cl20 2Na+Cl-
oxidant
Reducing agent – reductant- is the species causing the
reduction. This species is oxidized and can be called the electron
donor.
reductant
The number of electrons lost by the reductant must be equal to the
number of electrons gained by the oxidant.
e-
Dismutation (disproportionation)
The special case of oxidation – reduction reaction
a compound of intermediate oxidation state converts to two different
compounds, one of higher and one of lower oxidation states.
Examples:
The dismutation of superoxide free radical to hydrogen peroxide and oxygen,
catalysed in living systems by the enzyme superoxide dismutase
2 O2
.− + 2 H+ → H2O2 + O2
With oxidation numbers:
2 O2. −1 + 2 H+1 → H2
+1 O2-2 + O2
0
The dismutiation of hydrogen peroxide catalysed by the enzyme catalase
2 H2O2-2 → 2 H2O
-2 + O20
Oxidation-reduction reactions
Oxidation – reduction reactions occur together
Fe2+ + Cu2+ Fe3+ + Cu+
This reaction can be described in two half-reactions:
(1) Fe2+ Fe3+ + 1e-
(2) Cu2+ + 1e- Cu+
Which ion is a reducing agent (reductant)?
Reductant – donates electrons
Which ion is an oxidizing agent (oxidant)?
Oxidant – accepts electrons
Electron donor e- + electron acceptor
Conjugate redox pair
Biological oxidation-reduction reactions
In biological systems, oxidation is often synonymous with dehydrogenation
Many enzymes that catalyze oxidation reactions are oxidoreductases, called
dehydrogenases.
O : H ratio1 : 6
O : H ratio1 : 4
O : H ratio1 : 2
More reduced compounds are richer in hydrogen than in oxygen
More oxidized compounds have more oxygen and less hydrogen
The oxidation states of carbon in biomolecules
Most oxidized
Most reduced
Oxidation in organism can occur in one of four different ways:
1. Directly, as transfer of electrons
Fe2+ + Cu2+ Fe3+ + Cu+
2. As transfer of hydrogen atoms
H = H+ + 1e-
AH2↔ A + 2 eˉ + 2 H+
AH2+ B ↔ A + BH2
Hydrogen/electron donor
Reduced
3. As a transfer of hydride ion (Hˉ), which has two electrons (H+ + 2e-)
This occurs in the case of NAD-linked dehydrogenases
4. Through direct combination with oxygen
R−CH3+ ½O2 R−CH2OH
Reduction potentials
When two conjugate redox pairs are together in solution, electron transfer from the electron donor of one pair to the electron acceptor of the other may occur spontaneously.
The tendency for a reaction depends on the relative affinity of the electron
acceptor of each redox pair for electrons.
The standard reduction potential (E0) is the tendency for a chemical
species to be reduced, and is measured in volts at standard conditions
H+ + eˉ ½ H2 E0 = 0 V
The electrode at which this half-reaction occurs is arbitrarily assigned a
standard reduction potential of 0.00V.
Fe2+ + Cu2+ Fe3+ + Cu+
Element with the more positive redox potential has a higher
affinity towards electrons – it has an oxidizing property
Fe0 + Cu2+SO4 → Cu0 + Fe2+SO4
Element with the more negative redox potential has a lower
affinity towards electrons – it can easily donate electrons – it has
an reducing property
Reduction potentials
R is gas constant (8.314 JKˉ1molˉ1
T is temperature (Kelvin degree),
n is the number of electrons transferred per molecule
F is the Faraday constant (9.68 . 104 Cmolˉ1).
The Nerst – Peterson equation:
Reduction potentials in medicine
Known oxidation-reduction potentials of biological redox systems allow to
determine the direction and sequence of oxidation-reduction reactions
in biological systems.
The strict sequence of enzymatic reactions in “respiratory chain” allows a
gradual release of energy during biological oxidation.
Thank you for your attention...