colloids

Question 1

dispersed system

Answer 1

 Dispersed systems consist of particulate matter (dispersed phase), distributed throughout a continuous
phase (dispersion medium).
 They are classified according to the particle diameter (size) of the dispersed material;

Question 2

molecular dispertions

Answer 2

1- Molecular dispersions (less than 1 nm)
 Particles invisible in electron microscope
 Pass through semipermeable membranes and filter paper
 Particles do not settle down on standing or by centrifugation
 Undergo rapid diffusion (small sized particles)
 E.g. ordinary ions, glucose and nutrients and peptides in blood

Question 3

colloidal dispertions

Answer 3

2- Colloidal dispersions (1 nm - 0.5 μm)
 Particles not resolved by ordinary microscope, can be detected by electron microscope.
 Pass through filter paper but not pass through semipermeable membrane.
 Particles made to settle by centrifugation
 Diffuse very slowly e.g., natural and synthetic polymers

Question 4

colloids

Answer 4

 When the diameter of particle of a substance dispersed in a solvent range from 10 Å (1 nm) to 5000 Å
(0.5 μm), the system is termed as colloidal solution or colloidal dispersion or simply a colloid.
 A system with at least one dimension (length, width or thickness) of dispersed particles in the range
of 10 Å to 5000 Å is known as colloidal dispersion or colloids.

Question 5

coarse dispertion

Answer 5

3- Coarse dispersions (> 0.5 μ m)
 Particles are visible under ordinary microscope
 Do not pass through filter paper or semipermeable membrane.
 Particles settle down under gravity
 Do not diffuse e.g., emulsions, suspensions, red blood cells

Question 6

properties

Answer 6

 The colloidal solutions or colloids are intermediate between true solution and suspension.
 The substance distributed as colloidal particles is called as dispersed phase.
 And the second phase in which it is dispersed is called as dispersion medium.
 The dispersed phase and dispersion medium can be in either of three states of matter.
 Surface area of colloidal particles is much larger as compared to equal volume of larger molecules.

Question 7

types of sols or colloids

Answer 7

 Sols are special types of colloids in which dispersion medium is liquid and dispersed phase is solid.
There are three types of sols;
o Lyophilic sols or colloids
o Lyophobic sols or colloids
o Association sols or colloids

Question 8

lyophillic sols

Answer 8

 Lyophilic sols are those in which the dispersed phase exhibits an affinity for the solvent or the
dispersion medium.
 If in the lyophilic colloids, dispersion medium is water, then it will be called as hydrophilic colloids.
 The best example of lyophilic (hydrophilic) colloids are dispersion of acacia, gelatin or proteins in
water.

Question 9

properties of lyophillic colloids

Answer 9

 They can be obtained by direct mixing of dispersed phase into dispersion medium.
 There is no charge on the particles of hydrophilic colloids.
 The particles of dispersed phase of lyophilic sols are surrounded by dispersion medium particles and
solvation occurs.
 In hydrophilic colloids, dispersion medium is water, hence it is termed Hydration.
 Due to solvation, the lyophilic sols or colloids are viscous in nature.
 As lyophilic sols have smaller particles size so they don’t show Tyndall effect (scattering of light by
sol particles).
 They are reversible colloids, because when they coagulate, then they are again converted into colloidal
form.
 Acacia, insulin, albumin and gelatin are among those lyophilic colloids that bear organic molecules
and form colloidal solution in aqueous dispersion medium. (Hydrophilic)
 Rubber and polystyrene form lyophilic colloids in nonaqueous, organic solvents. (Lipophilic)

Question 10

lyophobic colloids

Answer 10

 Lyophobic colloids are solvent hating colloids.
 Those colloids in which the dispersed phase has no attraction for the medium or the solvent are called
as lyophobic sols or colloids.
 Examples of solvent hating (lyophobic colloids) are dispersion of gold, ferric hydroxide and sulphur
in water.

Question 11

propeties of lyophobic colloids

Answer 11

 They cannot be prepared by direct mixing of dispersed phase and dispersion medium.
 As there is no force of attraction between dispersed phase and dispersion medium, so solvation does
not occur in them.
 As there is no solvation in lyophobic colloids, so their viscosity is similar to dispersion medium.
 The particles of lyophobic colloids show tyndall effect.
 When the particles of hydrophobic sols are coagulated, they cannot again form colloidal solution. So
they are called as irreversible colloids.

Question 12

association or amphiphillic colloids

Answer 12

 The substances whose molecules aggregate spontaneously in a given solvent to form particles of
colloidal dimensions at a particular concentration are called as association colloids.
 In dilute solution the molecules of some substances such as soaps and artificial detergents are smaller
than the colloidal particles. But when this concentration is increased their molecules form aggregates
of colloidal size known as micelles. And this concentration at which aggregation occurs is called as
critical micelle concentration (CMC).
 At low concentration: Amphiphiles exist separately (sub-colloidal size)
 At high concentration: Form aggregates or micelles (50 or more monomers) (colloidal size)
 As with lyophilic sols, formation of association colloids is spontaneous, provided that the
concentration of the amphiphile in solution exceeds the CMC.

Question 13

amphiphiles may be

Answer 13

 Anionic (e.g., sodium lauryl sulfate or SLS)
 Cationic (e.g., cetyl triethylammonium bromide or CTAB)
 Nonionic (e.g., polyoxyethylene lauryl ether or POLE)
 Ampholytic (zwitterionic) e.g., dimethyl dodecyl ammonio propane sulfonate or DDAPS.

Question 14

preparation of colloids

Answer 14

 Due to attraction towards solvent molecules, lyophilic colloids can be prepared by simple mixing
method e.g. protein in water or gum in water are prepared by direct mixing of two substances
 On the other hand, lyophobic colloids due to lack of attraction towards solvent have specific methods
for their preparation
 Two important methods are
o Dispersion methods
o Aggregation or condensation methods

Question 15

dispertions methods

Answer 15

In this method, particle size is reduced by various methods to get particles of colloidal range. For this
purpose, various methods are used. Some are given below:
-collodial mills
-bredigs arc method or electro dispetion
-ultrasonic method
-peptozation methods ‘

Question 16

colloidal mills

Answer 16

o The solid along with dispersion medium is fed into a colloidal mill having two steel plates in
which one is at rest and other is moving or rotating at very high speed.
o Due to motion of moving steel plates the solid particles are ground to colloidal size and give
colloidal solution.
o By this method inks and colloidal graphite are formed

Question 17

bredigs ac method

Answer 17

o When electric arc is produced by two metal electrodes in water.
o The intense heat of spark vaporizes some metal and vapors condense under water and they
form colloidal range particles by aggregation.
o The water is kept cold by immersing the container in ice /water bath and trace of alkali (KOH)
is added. As it is present in water so hydrosols are formed. E.g., hydrophobic colloids of silver,
gold and platinum.
o “Purple of cassius” is a colloidal solution of gold and is formed by the reaction of gold salts
with tin(II) chloride

Question 18

ultrasonic method

Answer 18

o Ultrasonic vibrations with frequency range of 20,000 to 2,00,000 cps are used to prepare
colloidal sols. Mercury sols are prepared by disintegrating a layer of mercury into sol particles
in water by this process.
o Lipid nanoparticles (emulsomes) for targeted drug delivery are also prepared by this method.

Question 19

peptization

Answer 19

o The dispersal of precipitated material into colloidal solution by the action of an electrolyte in
solution is called peptization. OR
o Process of breaking up secondary particles (coagulates, aggregates or floccules) into primary
particles (colloids). OR
o Separation of particles from each other is called as peptization.
o It is a reverse process of coagulation.
o When powdered activated charcoal is added to water with stirring, the aggregated grains cannot
be completely broken up and the resulting suspension is gray and translucent.
o The addition of ≤0.1 percent sodium lauryl sulfate deflocculates the grains into finely dispersed
particles and results in a deep-black and opaque dispersion.
AgCl3 + H2O + AgNO3 → Ag sol. + HNO3
Fe(OH)3 + FeCl3 soln. → Fe sol. + 3HCl

Question 20

condensation method

Answer 20

 Sols are prepared from aggregation of true solution or molecular range particles to colloidal range.
 These consists of:
o Change of solvent
o Chemical reaction

Question 21

change of solvent

Answer 21

 Change in solvent to supersaturation leading to nuclei formation i.e. colloidal system formation
 Used to prepare colloidal dispersions of organic material like stearic acid and psudo-latex etc.
 Resin is present in molecular form in ethanol but in water these molecules precipitate out forming
colloidal range particles.
 Sulfur is insoluble in water but somewhat soluble in alcohol. When an alcoholic solution of sulfur is
mixed with water, a bluish white colloidal dispersion results.
 Weak basis and weak acids tend to solubilize in low and high pH, respectively, and likewise precipitate
(condense) above and below their respective pKa values.
 Depending upon the supersaturation of the nonionized bases or acids and the presence of stabilizing
agents, the resultant dispersions may be within the colloidal range.

Question 22

double decomposition

Answer 22

-double decomposition
-reduction
-oxidation
-hydrolysis

Question 23

double decomposition

Answer 23

 A reaction in which the positive ions and negative ions in two compounds switch partners to
form two new compounds.
 E.g., When hydrogen sulfide is passed through a solution of arsenic trioxide in distilled water,
we get a colloidal solution of Arsenic trisulfide.

As2O3 + 3H2S → As2S3 + 3H2O
 Process continues till yellow color of sol attains maximum intensity.

Question 24

reduction

Answer 24

 Silver and gold sols are prepared by treating dilute solutions of AgNO3 and AuCl3 with organic
reducing agents.

AgNO3 + tannic Acid  Ag sol
AuCl3 + tannic acid  Au sol
AuCl3 + SnCl3  2Au + SnCl4
AuCl3 + HCOH + H2O  Au + HCOOH

 In addition, the reduction of copper, mercury, platinum, rhodium, and palladium salts with
formaldehyde, hydrazine, hydroxylamine, hydroquinone, or stannous chloride form hydrosols
of these metals, which are strongly colored (e.g., red or blue)

Question 25

oxidation

Answer 25

 When Hydrogen Sulfide gas is made to pass through an aqueous solution of sulphur dioxide,
aqueous solution of sulfur colloids is obtained. It can also be obtained by passing the gas
through a solution of an oxidization agent such as bromine water as well as nitric acid.

SO2 + 2H2S → 3S + 2H2O
SO2 + Br2 (aq.) → S + 2HBr

Question 26

hydrolysis

Answer 26

 The chemical breakdown of a compound due to reaction with water.
FeCl3 (aq.) + 3H2O → Fe(OH)3 + 3HCl

Question 27

purification of colloids

Answer 27

 Sols or colloids prepared by various methods contain appreciable amount of electrolytes besides
colloidal particles
 These electrolytes tend to destabilize colloids so that’s why their purification is important
 These electrolytes can be removed by various methods to get pure sols
 Some of these methods are given below:
o Dialysis
o Ultrafiltration
o Electro-dialysis

Question 28

dialysis

Answer 28

 The process of removing ions from a sol by diffusing through a permeable membrane is called dialysis
 In this process, sol containing dissolved ions molecules or electrolytes is placed in a bag of permeable
membrane and dipping in pure water, the ions diffuse through the membrane
 By using a continuous flow of water, the concentration of electrolytes inside the membrane becomes
zero. So after some time all the electrolytes present in sol can be removed easily.

Question 29

factors affecting dialysis

Answer 29

The efficacy and speed of dialysis can be determined by the following factors;
 Increased surface of solution exposed to membrane
 Increased temperature
 Electric potential across the membrane
 Maximum concentration difference of dissolved substances across the membrane

Question 30

ultrafilteration

Answer 30

 Separation of sol particles from liquid medium and electrolyte by filtration through an ultra-filter is
called ultrafiltration
 It is a slow process which can be speeded up by increasing pressure (negative pressure). The colloidal
particles are left on the filter in the form of slime. The slime may be again added to fresh medium to
get back the pure sol.
 Ultra filter paper is a filter paper whose relatively larger pores are made small by using specialized
solvents e.g. nitrocellulose.
 It is also called as graded filter.
 Ultrafiltration is conducted under negative pressure (suction) through a dialysis membrane supported
in a Büchner funnel.

Question 31

electodialysis

Answer 31

 When dialysis and ultrafiltration are used to remove charged impurities such as ionic contaminants,
the process can be hastened by the use of an electric potential across the membrane. This process is
called electrodialysis.
 An electric potential may be used to increase the rate of movement of ionic impurities through a
dialyzing membrane and so provide rapid purification.
 Electrodialysis is carried out in a three-compartment vessel with electrodes in the outer compartments
containing water and the sol in the center compartment.
 Application of electrical potential causes cations to migrate to the negative electrode compartment and
anions to move to the positive electrode compartment, in both of which running water ultimately
removes the electrolyte.

Question 32

properties of sols (colloids)

Answer 32

Following are some important physical properties of lyophobic colloids:
 Optical properties
 Kinetic properties
 Electric properties

Question 33

optical properties

Answer 33

-tyndall effect
-electron microscopy
-light scarttering

Question 34

tyndal effect

Answer 34

o The phenomenon of scattering of light by the sol particles is called Tyndall effect & resulting
scattered became of light is called Tyndall became or Tyndall cone.
o Tyndall effect is very useful in determining the particle size of colloidal solution.
o True solutions do not show Tyndall effect because ionic or molecular sizes are very small &
so cannot scatter the light.
o Thus by using this phenomenon we can distinguish true solution & colloidal solution.

Question 35

electron microscopy

Answer 35

o In electron microscopy when a focused became of electrons is allowed to pass through a
colloidal solution.
o The size & shape of colloidal parties can easily be determined individually.
o By this process size & shape of several sol particles like paint pigments, viruses and bacteria
are determined.
o The resolving power of an electron microscope is very high resolving power 1/λ.
o Thus by decreasing λ (wavelength), resolving power in increased.

Question 36

light scattering

Answer 36

o This phenomenon can be explained on the basis of Tyndall EFFECT.
o When light is passed through colloidal system, it will be scattered & turbidity of system is
exulted.
o The fractional decrease in intensity due to scattering as the incident light passes through 1cm
of solution.
o By this we can calculate the size of particles & also their molecular weight, correlating with
turbidity, equation expressing this is

HC/T = 1/M +2BC

T = Turbidity C = Concentration of colloidal system
H = optical constant M = molecular weight of particle
B= interaction of the particles

Question 37

kinetic properties

Answer 37

The properties which are based on the motion of particles with respect to the dispersion medium are
called kinetic properties. Following are the same important kinetic properties of colloids:
-brownian movement
-diffusion
-osmosis
-sedimentation
-viscosity

Question 38

brownia movemnt

Answer 38

o The continuous rapid zigzag movements executed by a colloidal particle in the dispersion
medium is called the Brownian movement or motion.
o At any instant a colloidal particle is struck by several molecules of dispersion medium from
various directions.
o When vapour molecules struck on one side than other the particles change its direction of
motion.
o This constant pushing of particles by dispersion medium does not permit the particles to settle
down.

Question 39

diffusion

Answer 39

o The movement of particles from their higher concentration to lower concentration is known as
diffusion. It is the direct action of Brownian movements.
o And the amount of substance (colloid) moved from one place to another can be determined by
FLICK’s first law:

Dq = – DA dc / dx. dt

Dq = rate of diffusing substance D = diffusion coefficient
A = area of diffusion Dc /dx = conc. Gradient
Dt = time of diffusion

Question 40

osmosis

Answer 40

o It is special type of diffusion in which the particle moves from region of its higher concentration
to lower concentration through semi permeable membrane.
o The external pressure applied on solution to stop the osmosis of the solvent into solution
separated by a semi permeable Membrane is called osmotic pressure and this can be determined
by vent Hoff equation:

Π = NRt n = W/M
Π = W/M RT = M = WRT / Π
Π = osmotic pressure T = absolute temperature
R = gas constant M = molecular weight

Question 41

sedimentation

Answer 41

o The process by which the colloidal particle settles down in the dispersion medium due to force
of gravity is known as sedimentation.
o The velocity of sedimentation can be determined by following equation called stokes Law.
o Most colloids do not show the process of sedimentation b/c the particles are very small
sedimentation is opposed by their Brownian motion.
o However, sedimentation can be achieved by placing the particle in a high speed centrifuge.
o Thus gravitational Forces are replaced by centrifugal forces as much as 100000 times greater.

Question 42

viscocty

Answer 42

o Viscosity is a measure of fractional resistance offered by a system towards applied force.
o And it mainly depends upon the shape & size of particles of the system. In colloidal system,
the Lyophobic colloids are more viscous than solvents.
o The equation of flow for a dilute colloidal system can be written as:

n = no (1+2.5 ǿ)

N= viscosity of the total dispersion no = viscosity of the dispersion medium
ǿ = volume fraction = volume of dispersed phase / volume of dispersion medium

Question 43

electrical properties

Answer 43

The properties of colloids that depend upon the charge on colloids particles are called electric
properties of colloids.
 Electrical Double Layer: The combo nation of compact & diffused layer is called EDL. The
colloidal (sol) particles get a positive or negative charge by adsorbing positive or negative ion from
dispersion medium.
o For example: Fe(OH)3 sol are positively charged by adsorption of Fe 3 ions from Fecl3 use in
the preparation of sol.

 The force of repulsion between similar charges on colloidal particle prevents them to aggregate,
and to settle under the action of gravity.
o For example: the surface of colloids particle esquires’ positive charge by selective adsorption
of positive ion layer around it.
o The counter ions (which are negative in this case) form a layer around colloidal positively
charged particle & this is called stern layer or solvated layer or compact layer.

 The stern layer is surrounded by another layer of counter ions (positive in this case) this layer is called
diffused layer or Guy’s Chapman’s layer.
 The stern layer & diffused layer both are forming an electric double layer, which is very important for
stability of colloids by preventing them from coagulation.
 When different layers are formed on the charged colloidal particles, potential difference will also be
present between them. These are:
o Epsilon or Electro Kinetic Potential = sum of zeta potential & stern potential is called E.P.
o Zeta Potential: The potential difference between the compact layer diffused layer is called
zeta potential.
o Stern potential: The potential difference between compact layer & surface of the particle.

Question 44

electo-kinetic phenomenon

Answer 44

The phenomenon associated with the movement of charged particles through a dispersion medium or
with the movement of dispersion medium over a charged surface is called E.K.P.
1-electrophoresis
2-electro osmosis
3-steaming potential
4-sedimentation potential

Question 45

electrophoresis

Answer 45

 The movement of colloidal is applied across two platinum electrodes dipping in hydrophilic
colloids, the dispersed particles move towards one or the other electrode.
 If water is used as dispersion medium then by this process, we can determine the charge on sol
particles.
 E.g. metals, AS2S3, starch & clay are positively charged because they move towards positive
electrode while Fe(OH)3, Al(HO)3, basic dyes & haemoglobin are positively charged because
they move towards negative electrode.

Question 46

electro osmosis

Answer 46

 The movement of the dispersion medium under the influence of an applied potential is known
as electro-osmosis.
 It occurs due to the existence of zeta potential between the sol particles & the diffused layer
moves & causes electro osmosis.

Question 47

streaming potential

Answer 47

 When dispersion medium is made mobile between two electrodes, a potential difference is
produced between two electrodes & this is indicated by applying galvanometer in open circuit,
this type of potential is called streaming potential.

Question 48

sedimentaton potential

Answer 48

 When colloidal particles are settled down in the dispersion medium due to force of gravity (i.e.
sedimentation) a potential difference is created between top & bottom surfaces of colloidal
medium known as sedimentation potential.

Question 49

DLVO theory

Answer 49

 When two uncharged hydrophobic particles are in close proximity they attract each other by Vander
walls forces and if the particles are positive or negatively charged, they cause repulsion to the particles
of the same charges.
 If dispersion medium contains both the positive & negative charges, then they attract each other and
coagulation will occur.
 This theory explains the stabilization of colloids by electrostatic repulsion. This theory was suggested
by four scientists namely Derjaguin, Landau, very & over beak that’s why called DLVO theory.
 This theory is explained in the form of graph where VA AND Vr’’ represent the Vander walls attractive
energy & electrostatic repulsive energy respectively. Both of these energies decrease with the increase
of the distance of separation of the colloids.
 By the summation of attractive & repulsive forces between the colloidal particles, a net interaction
curve (ABCDEF) is resulted that explain the stability of colloids.
 The net curve indicates that as two particles approach each other (from d D to left side). The repulsive
potential predominates & will be called as energy barrier at point ‘’c’’ If K.E of particles exceeds the
potential energy barrier point ‘’C’’ then the distance between the particle decreases, the attractive
forces.

 Predominating & there will be irreversible flocculation at primary minimum & there will be un-
stability of colloids.

 On the other hand, if we go from pint C to right side, there is fall of repulsive forces & at a certain
distance de, there will also be flocculation of particles at secondary minimum but this type of
flocculation is called reversible flocculation.
Total energy:

VT = VA + VR

Where,
VA = Vander walls attractive forces, VR = electric repulsive forces.

Question 50

interaction of colloids

Answer 50

When two or more colloidal systems are mixed with each other, they interact and affect the properties
of each other. Some of such interactions are
1-mutual percipitation
2-conservation
3-sensitizatin
4-protection

Question 51

mutual percipitation of flocculation

Answer 51

 When two hydrophobic colloids having opposite charge are mixed with each other.
 The opposite charged particles will attract each other leading to coagulation.
 This type of coagulation is known as mutual precipitation or flocculation
 For example, when sulphur colloid (having –ve charged particles) mixed with colloidal solution
of Fe(OH)3 having +ve charges, flocculation will occur.

Question 52

conservation

Answer 52

 When two hydrophillic colloids with opposite charges are mixed together, the charged particles
will interact forming two layers
 Upper one is called colloidal poor layer
 Lower one is colloidal rich layer
 This process of separating the colloidal layers into two layers is known as coaservation
 For example, colloidal solution of acacia (-ve charge) with colloidal solution of gelatin (+ve
charge) at pH=3

Question 53

sensitization

Answer 53

 If a hydrophilic colloidal solution is added to hydrophobic colloidal solution in a very small
amount, the hydrophilic colloid will decrease the zeta potential of the hydrophobic colloid and
make them sensitive for instability and broken on the addition of electrolyte, this process is
called as sensitization.

Question 54

protection

Answer 54

 If in a mixture of hydrophilic and hydrophobic colloid, the conc. of hydrophilic colloid is
greater, it will stabilize the hydrophobic colloid on the addition of electrolyte and protects it
from breaking.
 The hydrophilic colloid which protects the hydrophobic colloid is called as protective colloid.
 E.g. 20% soln. of acacia (hydrophilic) will increase stability of hydrophobic sulphur colloid.
Acacia will thus be called as protective colloid

Question 55

factors affectin stabiity of colloids

Answer 55

 If in a mixture of hydrophilic and hydrophobic colloid, the conc. of hydrophilic colloid is
greater, it will stabilize the hydrophobic colloid on the addition of electrolyte and protects it
from breaking.
 The hydrophilic colloid which protects the hydrophobic colloid is called as protective colloid.
 E.g. 20% soln. of acacia (hydrophilic) will increase stability of hydrophobic sulphur colloid.
Acacia will thus be called as protective colloid

Question 56

presence of charge

Answer 56

 For stability of colloids the presence of charge on the surface of colloids is must
 In the absence of charge, the hydrophobic colloids will coagulate
 For this the dispersed particles of hydrophobic colloids contain a like electric charge +ve or –ve on
their surface
 Due to similar charges they will repel each other and system will be stable

Question 57

removal charge

Answer 57

 In dialysis, when charges are present in colloidal solution they are removed to purify and to be stable

Question 58

presence of solvent layer

Answer 58

 The presence of solvent layer around the particles of lyophilic colloids make them stable and on
addition of electrolyte they have a layer of solvent bound on the layer
 This solvent layer prevents the electrolyte to react with charge on particles and so also form
aggregation
 For example, gelatin particles have +ve charge and a layer of water bound to it
 When electrolyte (NaCl) is added, the water layer prevents the Na ions to react with gelatin so
aggregation does not occur
 This can also be exemplified by considering EDL which prevents coagulation

Question 59

addition of electrolyte

Answer 59

 When a small amount of electrolyte is added to a hydrophobic colloid the energy barrier of colloid is
decreased which cause flocculation of colloid by reduction of EDL
 When sufficient amount of electrolyte is added to hydrophobic colloid it will further decrease EDL
and energy barrier resulting in coagulation and instability

Question 60

schulz hardy rule

Answer 60

 Not only the amount of electrolyte but valency is also responsible for aggregation of particles.

Question 61

gold number

Answer 61

 Hydrophilic colloids are protective for hydrophobic colloids but the degree of protection varies and
determined by their Gold Number
 No. of milligrams of hydrophilic colloids that will just prevent the precipitation of 10mL of gold
solution on addition of 1ml of 10 % NaCl
 Onset of precipitation indicated by change in color from red to violet

Question 62

artifical kidney machine

Answer 62

 Patient’s blood (arterial) pass through Cellophane coils (ideal semi permeable membrane for
haemodialysis).
 Cellophane pass urea, glucose, electrolytes but don’t pass plasma proteins & blood cells
 Pure dialyzed blood enters the body again through a vein.
 Success of the artificial kidney machine depends on its ability to reduce blood urea.
 Cellophane coils are supported on a drum rotating in electrolyte solution (rinsing fluid).
 Cellophane is an ideal smei-permiable membrane for haemodialysis as its pore size is such that
electrolytes, urea and glucose all can pass freely across it, while the larger molecules such as plasma
proteins, lipid fraction and blood cells cannot pass.
 Cellophane tube cannot allow bacteria to pass across it, so that only the inside surface need
sterilization.
 Artificial kidney machine is used for the haemodialysis
 The success of artificial kidney machine depends upon the reduction of blood urea by passage of the
patient’s blood through the coils of cellophane tubing which is immersed in a suitable rinsing fluid
 The molecular composition is designed to create a diffusion gradient from blood to rinsing fluid of
substances which are present in excess in the blood (urea) and from the rinsing fluid to blood of the
substances which are deficient in the body (bicarbonate)
 While the concentration of those diffusible substances which are present in the normal amounts in the
blood is kept unaltered by having them present in same concentration as in rinsing fluid.
 The length of cellophane tubing is about 60m

Question 63

pharmaceutical applications

Answer 63

 Colloidal silver iodide, silver chloride & silver protein are effective germicides or antiseptics & not
cause irritation as ionic silver salts do.
 Colloidal copper is used as anticancer.
Chapter 4. Dispersions

119

Muhammad Muneeb
 Colloidal gold is used as diagnostic (radioactive) agent.
 Colloidal mercury used in syphilis.
 Association colloids are used to increase solubility & stability of certain compounds in aqueous &
oily pharmaceutical preparations.
 Efficiency of certain substances is increased when used in colloidal form due to large surface area. E.g.
efficiency of kaolin in adsorbing toxins from GIT. and efficiency of aluminum hydroxide as antacid.
 Blood plasma substitutes like dextran, PVP & gelatin are hydrophilic colloids and are used to restore
or maintain blood volume.
 Iron - dextran complex form non-ionic hydrophilic sols used for treatment of anemia.
 Therapy: Colloidal system are used as therapeutic agents in different areas.
o E.g. Silver colloid – Germicidal
Copper colloid – Anticancer
Mercury colloid – Anti-syphilis

Question 64

stability

Answer 64

o Lyophobic colloids prevent flocculation in suspensions.
o Colloidal dispersion of gelatin is used in coating over tablets and granules which upon drying
leaves a uniform dry film over them and protect them from adverse conditions of the
atmosphere.

Question 65

absorption

Answer 65

o As colloidal dimensions are small enough, they have a huge surface area. Hence, the drug
constituted in colloidal form is released in large amount.
o E.g.- sulphur colloid gives a large quantity of sulphur and this often leads to sulphur toxicity

Question 66

targetd drug delivery

Answer 66

o Liposomes are of colloidal dimensions and are preferentially taken up by the liver and spleen.

Question 67

photography

Answer 67

o A colloidal solution of silver bromide in gelatin is applied on glass plates or celluloid films to
form sensitive plates in photography.

Question 68

clotting of blood

Answer 68

o Blood is a colloidal solution and is negatively charged.
o On applying a solution of FeCl3 bleeding stops and blood clotting occurs as Fe+3 ions neutralize
the ion charges on the colloidal particles.