Download Colloids

COLLOids
Aqueous &Non-aqueous Solutions
Aqueous Solutions
Solutions that contain water as the solvent.
For example:
sugar in water, carbon dioxide in water, etc.
Non-aqueous Solutions
Solutions that contain solvent other than water .
Ether, benzene, petrol, carbon tetrachloride etc.,
are some common solvents.
For example:
sulphur in carbon disulphide, naphthalene in
benzene, etc.
Concentrated Solutions and Dilute
Solutions
The concentration of a solution is expressed as
the amount of solute present in a given amount
(mass or volume) of the solution; or the amount
of solute dissolved in a given mass or volume of
a solvent. It is expressed as a percentage of
these quantities.
Between two solutions, the solute quantity may be
relatively more or less. If the proportion of solute
is less, the solution is said to be dilute.
Solutions
True Solutions:
A true solution is a homogeneous solution in which the
solute particles have diameters between 0.1 nm to 1 nm
i.e., the solute particles are of molecular dimensions.
Such dispersed particles dissolve in solution to form a
homogenous system. These do not settle down when the
solution is left standing. The particles are invisible even
under powerful microscopes and cannot be separated
through filter paper ,parchment paper or animal
membranes. For example, sodium chloride in water is a true
solution. Most ionic compounds form true solutions in water.
Organic compounds like sugar and urea also form true
solutions in water.
http://academic.pgcc.edu/~ssinex/Solutions.ppt
Comparison of Solutions, Colloids, and Suspensions
< 1 nm
solutions
-single atoms
-small molecules
-ions
-polyatomic ions
> 100 nm
colloids
-aggregates of
atoms, molecules
or ions
-macromolecules
(proteins)
suspensions
-clumps of
particles,
-mineral grains
such as sand
Suspensions
• Suspensions consist of particles of a solid suspended in
a liquid medium. Suspensions are systems with two
distinct phases. The particles in suspensions are bigger
than 100 nm to 200 nm across. The particles of a
suspension may not be visible to the naked eye but are
visible under a microscope. Suspensions are
heterogeneous systems. They stay only for a limited
period i.e. these are not stable as the particles have a
tendency to settle down under the influence of gravity.
The particles of a suspension can neither pass through
ordinary filter paper nor through animal membranes.
• Examples of suspensions are sodium chloride in
benzene, turmeric in water, silver chloride, barium
sulphate or sand in water.
Colloidal solution or colloidal state or
colloidal dispersion
They represent an intermediate kind of a mixture between
true solution and suspension. The size of a colloidal
particle lies roughly between 1-100 nm. Colloids are
also a two-phase heterogeneous system consisting of
the dispersed phase and dispersion medium.
Colloidal solution or colloidal state or colloidal
dispersion
Since the dispersed phase in a colloidal system is uniformly
distributed in the dispersion medium, the colloidal state
appears homogenous to the naked eye or even an
ordinary microscope (due to particles being invisible).
However it is a heterogeneous dispersion of two
immiscible phases and this is proved by viewing it under
an ultra-microscope, where the light reflected by colloidal
particles can be seen. Colloidal particles do not settle
down under gravity: a colloidal solution of gold prepared
by Faraday over 125 years ago continues to be in
excellent condition even today. Colloids can pass
through ordinary filter paper but do not pass through
animal membranes.
Difference Between True Solutions,
Suspensions and Colloidal Solutions
http://academic.pgcc.edu/~ssinex/Solutions.ppt
< 1 nm
solutions
transparent
(clear)
molecular motion
never settle
> 100 nm
colloids
transparent with
Tyndall effect
Brownian motioncolloidal particles
moved by solvent
coagulation – can settle
suspensions
translucent
(cloudy)
movement by
gravity
Classification of Colloids Based
on Type of Phases
Each of the two phases of a heterogeneous
colloidal system i.e., the dispersed phase and
dispersion medium, can be in any one of the
three physical states of matter. We have eight
different types of colloidal solutions (not nine),
since a colloidal state of gas-in-gas forms a
single phase (gases consist of molecules, and
with molecules of both gases mixing in all
proportions, two separate phases do not form).
http://academic.pgcc.edu/~ssinex/Solutions.ppt
Using whole blood as an example…
solutions
-dissolved in water
electrolytes
(salts)
gases
glucose
colloids
-plasma proteins
albumins
globulins
fibrinogen
suspensions
-cellular stuff
red blood cells
white blood cells
platelets
Types of Colloidal Solutions
Properties of Colloids
1. Heterogeneity
A colloidal solution is heterogeneous system
consisting of two phases of dispersed
phase (colloidal particles of a solid) and
the aqueous dispersion medium. Often a
colloidal sol appears to be homogeneous
as the particles are small in size and not
visible to the naked eye. However, this is
disproved when it is viewed under
electron microscope.
Properties of Colloids
2-Stable nature
Colloidal solutions are quite stable. The colloidal
particles do not settle at the bottom under the
influence of gravity. This is because of the
constant motion of colloidal particles.
3-Filterability
Colloidal particles do not pass through ultrafilter
papers, animal and vegetable membranes. The
large pore size of ordinary filter paper enables
colloidal particles to pass through.
Colligative properties
In colloidal systems the number of colloidal
particles per liter of the sol is relatively much
smaller than solute particles in a true solution.
Colloidal particles are aggregates of simple
molecules and colligative properties such
elevation in boiling point, depression in freezing
point and lowering of vapour pressure depend
upon the number of colloid particles present in
system and not on the nature of the particle. The
values of colligative properties are consequently
much smaller as compared to true solutions.
Mechanical Properties (Brownian movement)
• When colloidal solutions have been
observed through ultra microscope, the
colloidal particles are seen in constant and
rapid zigzag motion called Brownian
movement. Sir Robert Brown first
observed the phenomenon in 1827.
Suspensions and true solutions do not
exhibit Brownian movement.
Optical Properties (Tyndall Effect)
When a strong beam of light is passed
through a colloidal solution, the path of the
light becomes visible when viewed from a
direction at right angle to that of the
incident light. This occurs because the
colloidal particles absorb light energy and
then scatter it in all directions. The
phenomenon of scattering of light by sol
particles to form illuminated beam or cone
is called Tyndall effect or Tyndall beam or
Tyndall cone.
http://academic.pgcc.edu/~ssinex/Solutions.ppt
< 1 nm
solutions
> 100 nm
colloids
suspensions
Absorption of light
Passage of light
Scattering in beam
Scattering in
all directions
Electrical Properties (Electrophoresis)
Colloidal particles of a sol either carry positive or negative
charge. Sols in, which the colloidal particles carry positive
charge are called positive sols. When colloidal particles carry
negative charge, the sols are called negative sols. The
existence of charge on the colloidal particles can be
demonstrated by a phenomenon called electrophoresis
where the colloidal particles, when placed in an electric field,
move towards either cathode or anode depending upon the
charge on them. Sols of basic dyestuffs, ferric hydroxide,
aluminium hydroxide etc., are some common examples of
positive sols. Colloidal solutions of gums, starch, soap
solution, metals (Ag, Cu, Au, Pt etc.), metal sulphides, and
some acid dyestuffs are the examples of negative sols
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