Rheology, Viscosity, Shearing Stress, Dispersed System, Colloidal Dispersion, Colloids & Coarse Dispersion.
Rheology:
Rheology is the
study of the flow and deformation properties of the matter.
Viscosity:
The viscosity of
a fluid is its resistance to flow or movement.
According to
flow, fluids are of two types. They are:-
1.
Newtonian
Fluids &
2.
Non-
Newtonian Fluids.
1. Newtonian Fluids:- Liquids which follow
Newton’s law of viscous flow are known as newtonian’s liquids.
2.
Non-Newtonian
Fluids:- Liquids which do not follow Newton’s law are known as non-newtonian
fluids.
Example:
Colloidal dispersion, emulsions, suspensions and ointments.
Shearing Stress:
The force per
unit area F/A required to bring about flow is called the “Shearing Stress”
·
The
flow properties of Non-Newtonian Materials are three types. They are:-
1.
Plastic
flow
2.
Pseudo
plastic flow
3.
Dilatants
flow.
Dispersed System:
A dispersed
system is defined as a system in which one phase, the dispersed phase, is
distributed uniformly as particles throughout another phase, called the
sispersion medium or continuous phase.
Colloidal Dispersion:
If the particles
have a size ranging from 1 nm to 1 µm, which is dispersed in the continuous
phase, this system is called colloidal dispersion.
Colloids:
The particles
have a size ranging from 1 nm to 1 µm is called colloids.
Because of their large surface area, colloids show greater efficiency
for absorption or adsorption.
|
Coarse Dispersion:
The size of the
dispersed particles ranging from 1 µm to 100 µm, which is dispersed in the
continuous phase, this system is called coarse dispersion.
Parts, Molarity, Molality, Normality, Moles, Mole fraction, Mill/equivalents and normal solutions, Percent, ppm, ppb, ppt & ppq.
Parts
Pharmacopoeias
express some concentrations in terms of the number of 'parts' of solute
dissolved in a stated number of 'parts' of solution.
Molarity : Moles of solute
per liter of solution.
[Example:
Molecular weight of NaOH is “40” (Na=23; O=16; H=1). When the unit of this
number is expressed as “gram” and when this 40 gm of NaOH is dissolved in 1
liter solution this is called “1 molar NaOH Solution”
Molality : Moles of solute
per kilogram of solvent.
[Example:
Molecular weight of NaOH is “40” (Na=23; O=16; H=1). When the unit of this
number is expressed as “gram” and when this 40 gm of NaOH is dissolved in 1 kilogram
of solvent this is called “1 molal NaOH Solution”
Normality : Equivalent
weight of solute per liter of solution.
[Example:
Molecular weight H2SO4 is “98” (and equivalent weight of H2SO4
is “46”. When the unit of this number is expressed as “gram” and when
this 46 gm of H2SO4 is dissolved in 1 liter solution this
is called “1 normal H2SO4 Solution”
Moles : When the
molecular weight of a compound expressed as mass and unit is “gram”, then this
amount is called as mole of that compound.
Mole fraction
This is often
used in theoretical considerations and is defined as the number of moles of
solute divided by the total number of moles of solute and solvent, i.e.:
n1
mole fraction of
solute ( x1 ) = -----------
n1
+ n2
where n\ and
n2
are
the numbers of moles of solute and solvent, respectively.
Mill/equivalents and normal solutions
The concentrations
of solutes in body fluids and in solutions
used as replacements for those fluids are usually expressed in terms of the
number of millimoles (1 millimole = one thousandth of a mole) in a litre of
solution. In the case of electrolytes, however, these concentrations may still
be expressed in terms of milliequivalents per litre. A milliequivalent (mEq) of
an ion is, in fact, one thousandth of the gram equivalent of the ion, which is
in turn the ionic weight expressed in grams divided by the valency of the ion.
Alternatively,
ionic weight in mg
1mEq =
----------------------------
valency
Percent:
One part per hundred is
generally represented by the percent (%) symbol and denotes one part per 100
parts, one part in 102
ppm:
One part per moillion (ppm)
denotes one part per 1,000,000 parts, one part in 106; One ppm is
equivalent to 1 milligram of something per liter of water (mg/l) or 1 milligram
of something per kilogram solid (mg/kg) (1/1,000,000)
ppb:
One part per billion (ppb) denotes one part per
1,000,000,000 parts, one part in 109, One ppb represents one microgram
of something per liter of water (ug/l), or one microgram of something per
kilogram of solid (ug/kg). (1/1,000,000,000)
ppt:
One part pertrillion (ppt)
denotes one part per 1,000,000,000,000 parts, one part in 1012
(1/1,000,000,000,000).
ppq:
One part per quadrillion (ppq) denotes one part per
1,000,000,000,000,000 parts, one part in 1015 (1/1,000,000,000,000,000).
Dissolution, Factors affecting the rate of dissolution, Solubility & Types of Solubility.
Dissolution and
Solubility:
Solution:
Solution is the homogenous mixture of solute and solvent.
Generally
the largest portion of the solution is called solvent and the smallest portion
which is dissolved is the solvent is called solute.
Dissolution:
The transfer of molecules or ions from a solid state into solution is known as
dissolution.
Factors
Factors affecting the
rate of dissolution:
1. Size
of solid particles.
2. Dispersibility
of powdered solid in dissolution medium.
3. Porosity
of solid particles.
4. Temperature
5. Nature
of dissolution medium.
6. Molecular
structure of solute.
7. Crystalline
form of solid.
8. Volume
of dissolution medium.
9. pH
Solubility:
The solubility of a substance is the maximum amount of that substance
which can dissolve in a certain amount of solvent definition
A good solvent
is usually based on the 'like dissolves like' principle, that is, a solute
dissolves best in a solvent with similar chemical properties. The concept
traditionally follows two rules:
1.
Polar
solutes dissolve in polar solvents.
2.
Non-polar
solutes dissolve in non-polar solvents.
Determination of
the solubility of a solid in a liquid
The following
points should be observed in all solubility determinations:
1.
The
solvent and the solute must be pure.
2.
A
saturated solution must be obtained before any solution is removed for
analysis.
3.
The
method of separating a sample of saturated solution from undissolved solute
must be satisfactory.
4.
The
method of analysing the solution must be reliable.
5.
Temperature
must be adequately controlled.
Types of Solubility:
Description
|
Approximate weight of solvent (ml)
necessary to dissolve 1 g of solute
|
|
Very
soluble
|
<
1
|
less than 1 ml solvent is
required to dissolve 1 gm of solute
|
Freely
soluble
|
Between
1 and 10
|
Solvent between 1 ml to 10 ml is
required to dissolve 1 gm of solute
|
Soluble
|
Between
10 and 30
|
Solvent between 10 ml to 30 ml
is required to dissolve 1 gm of solute
|
Sparingly
soluble
|
Between
30 and 100
|
Solvent between 30 ml to 100 ml
is required to dissolve 1 gm of solute
|
Slightly
soluble
|
Between
100 and 1000
|
Solvent between 100 ml to 1000
ml is required to dissolve 1 gm of solute
|
Very
slightly soluble
|
Between
1000 and 10 000
|
Solvent between 1000 ml to 10
000 ml is required to dissolve 1 gm of solute
|
Practically
insoluble
|
>
10 000
|
Greater than 10 000 ml solvent is required to
dissolve 1 gm of solute
|
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