3. Molarity
Number of moles of solute present in
one litre of solution.
Moles of solute
M
Volume (in litre)
=
Moles of solute 1000
M
Molecular mass volume (in ml)
×
=
×
Moles = Molarity x volume (in litre)
Milli moles = Molarity x volume (in ml)
4. Illustrative example
Calculate the molarity of a solution of
NaOH in which 0.40g NaOH dissolved
in 500 ml solution?
A sample of NaNO3 weighing 8.50 grams is placed in a 500. ml
volumetric flask and distilled water was added to the mark on the
neck of the flask. Calculate the Molarity of the resulting solution.
5. Relation between normality and
molarity
Mass of solute 1000
N
Molecular mass
volume (in ml)
n factor
×
=
×
N = M x n factor
For HCl, n = 1
H2SO4, n = 2
H3PO4, n = 3
NaOH, n = 1
Ca(OH)2, n = 2
For monovalent compound (n = 1)
Normality and molarity is same.
6. Molality
Number of moles of solute present in 1 Kg
(or 1000 gram) of solvent. It is represented
by m (small letter).
Moles of solute
m
Mass of solvent
=
7. Illustrative Problem
Calculate the molality of 1 molar solution of NaOH given
density of solution is 1.04
gram/ml.
Determine the molality of 3000 grams of solution containing 37.3
grams of Potassium Chloride KCl.
9. Gram Equivalent weight
Equivalent mass is equal to the molecular or atomic mass divided by
the number of electrons involved in the reaction per molecule, atom
or ion. For example in the reaction,
two electrons are needed to produce one molecule of hydrogen gas.
So, 2 Faraday of electricity is needed to produce one mole of
hydrogen gas.
Hence,
10. Molarity = Moles of solute/Liters of Solution (M)
Molality = Moles of solute/Kg of Solvent (m)
Mole Fraction = Moles solute/total number of moles
Mass % = Mass solute/total mass x 100
Volume % = volume solute/total volume x 100
ppm = parts per million *
ppb = parts per billion *
29. Staining tests
If a water-soluble dyes is added in an o/w emulsion the emulsion takes
up the color uniformity, phase is continuous phase.
Conversely if the emulsion is w/o type and dye being soluble in water,
the emulsion takes up the color only in the dispersed phase and the
emulsion is not uniformly colored. W /O emulsion
O/W emulsion
30. Fluorescence Method
Many oils fluoresce under ultraviolet
light. Thus, if the whole field
fluoresces under fluorescent light
microscope, the emulsion is w/o, if,
on the other hand, only a few
fluorescent dots are evident, the
emulsion is o/w.
Wetting of Filter Paper Method
This method depends on the respective abilities of oil and water to wet filter
paper. A drop of the emulsion is placed on a piece of filter paper; if the liquid
spreads rapidly, leaving a small drop at the center, the emulsion is o/w. If no
spreading occurs, the emulsion is w/o.
O/W emulsion
W /O emulsion
31. Stability of Emulsions
What are the characteristics of a stable emulsion?
A stable emulsion is one in which:
-dispersed globules retain their initial character
-and remain uniformly distributed throughout the continuous
phase.
Thus change in number of dispersed globules
Change in size of globules
Change in globule size distribution (polydispersity index)
and change in viscosity means unstable emulsions.
33. Creaming and Sedimentation:
• This process results from external forces, usually
gravitational or centrifugal.
• When such forces exceed the thermal motion of the
droplets (Brownian motion), a concentration gradient
builds up in the system such that the larger droplets
move more rapidly either to the top resulting in
CREAMING (if their density is less than that of the
medium)
• or to the bottom resulting in SEDIMENTATION (if their
density is greater than that of the medium) of the
container.
Physical Instability:
34. Physical Instability: Creaming & sedimentation
Creaming and sedimentation results temporary changes of emulsion into two
regions, one of which is richer in the disperse phase than the other e.g. the
creaming of milk, when fat globules slowly rise to the top of the product.
Creaming and sedimentation are reversible process.
Velocity of the creaming and sedimentation is governed by Stokes’ law
g = gravity constant
r = radius of the dispersed globules
η = viscosity of the external phase
ρ = density of the internal phase
ρo= density of the external phase
v = velocity of sedimentation of the dispersed spherical particles
V =
2 r2
(ρ - ρo) g
9 η
35. B- Coalescence (Breaking, Cracking)
Process of thinning and disruption of the liquid
film between the droplets, with the result that
fusion of two or more droplets occurs to form
larger droplets.
Cracking or coalescence of an emulsion leads to
the separation of dispersed phase as a layer.
Cracking is a irreversible process (permanent loss) .
36. Preventing Coalescence (Breaking, Cracking)
The coalescence of oil globules in an o/w emulsion is
resisted by the presence, of a mechanically strong
adsorbed layer of emulsifier around each globule.
37. • Flocculation : Aggregation of the droplets (without any
change in primary droplet size) into larger units.
• Flocculation occurs when there is not sufficient
repulsion to keep the droplets apart at distances
where the van der Waals attraction is weak.
• Ostwald Ripening: Aggregation of the droplets with
change in primary droplet size.
• With emulsions which are usually polydisperse, the
smaller droplets will have a greater solubility when
compared to larger droplets (due to curvature effects).
• With time, the smaller droplets disappear and their
molecules diffuse to the bulk and become deposited on
the larger droplets.
Physical Instability: Flocculation & Ostwald ripening
38. O/W→ W/O
• Nature of emulsifier: Making the emulsifier more oil soluble tends to
produce a W/O emulsion and vice versa. (Bancroft's rule)
• Phase volume ratio
Oil/Water ratio ↑ →W/O emulsion and vice versa.
• Temperature of the system: ↑ Temperature of O/W makes the
emulsifier more hydrophobic and the emulsion may invert to W/O.
• Addition of electrolytes and other additives: Addition of Strong
electrolytes to O/W (stabilized by ionic surfactants) may invert to
W/O
Example. Inversion of O/W emulsion (stabilized by sodium cetyl sulfate
and cholesterol) to a W/O type upon addition of polyvalent Ca.
Physical Instability: Inversion of Emulsions
(Phase inversion)
39. 2- Chemical Instability of Emulsion
1) Chemically incompatibility of the emulgent system with the active agent
and with the other emulsion ingredients
• Ionic emulsifying agents are usually incompatible with materials of
opposite charge. i. e. anionic and cationic emulgents .
• Addition of electrolyte may cause salting out of the emulsifying agent or
phase inversion e.g. sodium soap stabilize o/w emulsion so when a divalent
electrolyte such as CaCl2 is added it may form the calcium soap, which
stabilize a w/o emulsion.
• Emulgents may also be precipitated by the addition of materials in which
they are insoluble e.g. precipitation of hydrophilic colloids by the addition
of alcohol.
• Changes in pH may also lead to the breaking of emulsions. Sodium soaps
may react with acids and produce the free fatty acid and the sodium salt of
the acid. Soap-stabilized emulsions are therefore usually formulated at an
alkaline pH.
40. 2) Oxidation
Many of the oils and fats used in emulsion formulation are of
animal or vegetable origin and can be susceptible to oxidation
by:
Atmospheric oxygen or .
By the action of microorganisms.
The resulting rancidity is manifested by the formation of
degradation products of unpleasant odour and taste.
This can be controlled by the use of:
Antioxidants.
Antimicrobial preservatives.
2- Chemical Instability of Emulsion
41. 3) Microbiological Contamination
Microbial contamination may causes:
Gas production.
Colour and odour changes.
Hydrolysis of fats and oils.
pH changes in the aqueous phase.
Breaking of the emulsion.
Why it happens?
Some of the hydrophilic colloids (emulsifying agents) may provide a suitable
nutritive medium for microorganisms.
Most fungi and many bacteria will multiply readily in the aqueous phase of an
emulsion.
o/w emulsions tend to be more susceptible to microbial spoilage than w/o products,
why? In w/o emulsions the continuous oil phase acts as a barrier to the spread of
microorganisms throughout the product, and the less water there is present the less
growth there is likely to be.
Therefore an antimicrobial agent must be added.
2- Chemical Instability of
Emulsion
42. 4) Adverse Storage Conditions
Increase in temperature will causes:
An increase in the rate of creaming, due to a fall in
apparent viscosity of the continuous phase.
increased kinetic motion of the dispersed droplets thus the
number of collisions between globules will increase
The emulsifying agent at the oil/water interface will result
in a more expanded monolayer, and so coalescence is more
likely.
Certain macromolecular emulsifying agents may be
coagulated.
Decrease in temperature may cause:
Precipitation of certain emulgents.
2- Chemical Instability of Emulsion….
43. Stability Testing of Emulsions
1) Macroscopic Examination
Examination of the degree of creaming or coalescence occurring over a period
of time.
This is carried out by calculating the ratio of the volume of the creamed or
separated part of the emulsion and the total volume.
2) Globule Size Analysis
Microscopic examination - Coulter counter - laser diffraction sizing are most
widely used to determine the mean globule size as an increase with time is a
sign for coalescence.
3) Viscosity Changes
Any variation in globule size or number or in the orientation or migration of
emulsifier over a period of time may be detected by a change in apparent
viscosity.
In order to compare the relative stabilities of similar products it is often
necessary to speed up the processes of creaming and coalescence by
temperature cycling or centrifugation.
