Physio-chemical processes

1. Physio-Chemical Processes
Dr Nasir Abbas

2. Course Outline & Topics to be covered :
1. Precipitation
2. Ignition
3. Distillation
4. Vaporization
5. Evaporation
6. Dessication
7. Levigation
8. Trituration
9. Efflorescence
10. Exiccation

3. Contd…..
11 Deliquescence
12 Fusion
13 Crystallization
14 Lyophillization
15 Adsorption
16 Sublimation
17 Elutriation
18 Calcination
19 Decantation .

4. 1. Precipitation .
General Introduction :
• Crystallization and precipitation are two similar concepts , which are
used as separation techniques.
• In both the methods , the end product is a solid and its nature can be
controlled by manipulating different variables throughout the
process.
• Precipitation is a unit process in which a settleable and/or filterable
solid is formed by the chemical joining of two or more inorganic
dissolved chemical species , the objective of which is to remove one
of the chemical species .

5. Contd…
Process
• Precipitation occurs when solutions of materials which react
chemically are mixed to form a product which is sparingly soluble in
the liquid and therefore deposits out.
• When the reaction occurs in a liquid, the solid formed is called the
Precipitate (but when subjected by a centrifuge, it is called as a
pellet.)
• The liquid remaining above the solid is in either case is called the
supernatant.

6. Contd…
• Precipitation is a convenient method for producing solids in a very
fine state of subdivision – up to 0.1 μm in diameter
• The substances produced by the process of precipitation are usually
microcrystalline.
• On laboratory scale, precipitation is best performed in a conical
beaker. The form of which is most convenient for washing the
precipitate by decantation before collecting it on a filter paper.

7. Contd…
• In precipitation reactions, two compounds exchange parts in a
solution to form a solid precipitate. The general form of the equation
for such a reaction is;
AB + CD --------- AD + CB
• In a precipitation reaction one product is insoluble in water. As the
product forms, it emerges, or precipitates from the solution as a solid.
The solid is called as a precipitate e.g.,
Ca(NO3)2 (aq) + Na2CO3 (aq) --------- CaCO3 (s) + 2NaNO3 (aq)

8. Contd….
• The solubility rules are used to determine whether precipitation
reactions occur or not.
• When chemically equivalent quantities of the reactants are used,
then the order of mixing is usually not of much importance.
• When an excess of one reactant is required for complete precipitation
of the product, this reactant is usually gradually added to the other
reactant until no further precipitate is produced. This procedure
avoids waste of materials and the precipitate formed will require less
washing in order to obtain it in a pure condition.

9. Contd….

10. Contd…..
• If we add a solution of KCl to an AgNO3 solution the precipitate will form.
KCl(aq) + AgNO3(aq) --------- KNO3 + AgCl(s)
• When we look at the solubility table to see if any of the products are
insoluble in water, we see that the table indicates that AgCl is insoluble -
most chlorides are soluble except for Ag+, Hg2+and Pb2+. The molecular
equation then becomes:
KCl(aq) + AgNO3(aq) ---------- KNO3(aq)+ AgCl(s)
• The net ionic equation is:
Cl-(aq) + Ag + (aq) ---------- AgCl(s)
• If we add a solution of NaNO3 to an NH4Cl solution the precipitate will not
form. The equation then becomes:
NaNO3 (aq) + NH4Cl (aq) ---------- NaCl + NH4NO3

11. Contd….
• We see that the table indicates that both compounds are soluble
• Most chlorides are soluble, NaCl is soluble, nitrates are soluble as well
as NH4+ compounds, so mixing these two solutions gives no
precipitates and no reaction results.
• A precipitate (ppt) will generally form when two solutions are mixed
and if one solution has a strong positive charge (+2 or +3) and the
other solution has a strong negative charge (-2 or -3).
• The distinction between precipitation and crystallization is quite often
based on the speed of the process and the size of the solid particles
produced.

12. Contd…
• The term precipitation commonly refers to a process which results in
rapid solid formation that can give small crystals that may not appear
crystalline to the eye, but still may give very distinct x-ray diffraction
peaks.

13. Contd….
• The character/nature of a precipitate usually depends upon the conditions
under which it has been produced.
• When the reacting substances are mixed at temperatures near to their
boiling points, the precipitate produced is usually granular and heavy.
• On the other hand, the precipitate of the same substance produced by
mixing cold solutions may be light, take a long time to settle and wash. It
may also pass through the filter.
• Similarly, concentrated solutions produce a precipitate with larger
particles, than do the dilute solutions.
• Some substances can be precipitated from cold solutions only e.g.,
potassium tartarate and magnesium ammonium sulphate.

14. Contd…
Example
• Let we have two solutions; one of sodium carbonate and one of calcium chloride.
• Both ionic substances are soluble because they have at least one weak (+1 or –1)
ion each.
• Sodium carbonate is made of Na+1 and CO3-2 ions, so is soluble because of the
sodium while calcium chloride is made of Ca+2 and Cl-1 so also is soluble due to
the chloride ions.
• Each solution by itself is soluble because of the presence of a +1 or –1 charge.
• But after mixing Ca+2 having a strong positive charge is in the same beaker with a
strong negative charge, CO3-2 , the strong charges are looking for other strong
charges to bond with, these two ions can bond together to form a brand new
compound: Ca+2 CO3-2 or CaCO3.

15. Contd….
• The calcium and carbonate ions bond strongly together to form the
precipitate of calcium carbonate.

16. Contd…
Example 2
• Let we now have two solutions of NaCl and Mg(NO3)2.
• When they are mixed together, we do not get a cloudy result in the
beaker; because their mixing did not form a precipitate.
• In order to form a precipitate we need a strong positive charge and a
strong negative charge.
• The magnesium is a strong positive charge looking for a strong
negative but it is not there. There is no strong negative charge
present. Thus, no precipitate forms and the solution does not get
cloudy.

17. Contd…..
• These are general rules that do not work in all circumstances.

18. Contd…
Applications :
• In preparation of pharmaceuticals, dyes, paints, printing inks.
• Precipitation reactions can be used for making pigments, in water
treatment, and in qualitative inorganic analysis.
• Many consumer products are produced via precipitation processes, such as
magnetic recording media, which contain ferric or chromic oxides, and
photographic materials.
• Precipitation has also played an important role in wastewater treatment
(e.g., removal of calcium salts).
• Precipitation is also useful in purifying products.
• In metallurgy, precipitation from a solid solution is also a useful way to
strengthen alloys; this process is known as solid solution strengthening.

19. 2. Ignition
• It is also called as incineration
• It is the process by which an organic substance is strongly heated until
whole of the carbonaceous matter burns and an inorganic residue
known as Ash is left behind.
• This is a process of heating the organic substances in excess of air,
until all the Carbon atoms have burnt as CO2 and residue of inorganic
matter (Ash) is left behind. The residue is called as Ash and the
process as Ashing.
• On laboratory scale ignition is carried out in silica or platinum
crucibles.

20. Contd…
• It consists of strongly heating ("igniting") a sample of the material at a
specified temperature, allowing volatile substances to escape, until its
mass ceases to change. This may be done in air, or in some other
reactive or inert atmosphere.
Process :
• The simple test typically consists of placing a few grams of the
material in a tarred, pre-ignited crucible and determining its mass,
placing it in a temperature-controlled furnace for a set time, cooling it
in a controlled (e.g. water-free, CO2-free) atmosphere, and re
determining the mass.

21. Contd …..
Applications :
• This process is mainly used for the standardization of organic
substances and crude drugs by means of gravimetric analysis.
• Used to determine impurities of organic salts of alkali metals such as
tartarates, citrates, Benzoates and many drugs.
• Purity of a drug is determined by its ash content.

22. 3. Distillation
General Introduction :
• Distillation is the process in which a liquid is vaporized (turned to
vapours), re condensed (turned back into a liquid) and collected in a
container.
• Distillation may be defined as the separation of the constituents of a
mixture including a liquid by partial vaporization of the mixture and
separate collection of the vapors.

23. Contd…..
1: Heat source 2: Still pot 3: Still head 4:
Thermometer/Boiling point temperature
5: Condenser 6: Cooling water in 7: Cooling water out 8:
Distillate/receiving flask
9: Vacuum/gas inlet 10: Still receiver 11: Heat control 12:
Stirrer speed control
13: Stirrer/heat plate 14: Heating (Oil/sand) bath 15: Stirrer
bar/anti-bumping granules
16: Cooling bath.

24. Contd….
• The separations may include;
Separation of a liquid from non-volatile impurities.
The separation of a liquid from one or more other liquids, with which
it may be miscible, partially miscible or immiscible.
• The process of vaporizing a liquid mixture in one vessel and
condensing the vapors into another vessel is called distillation.
• The liquid being distilled is heated in a flask, which is sometimes
called a distillation flask or distillation pot or Still.

25. Contd….
• The vapors are condensed on a cool surface, usually a water-cooled
condenser.
• The resulting liquid is called the distillate and is collected in a
receiving flask or Receiver.

26. Contd…
• The boiling point of mixtures depends upon mole fraction of the
component present i.e :
a) In pure substances the temperature remains constant during
distillation process so long as both vapor and liquid are present.
b) In miscible liquid mixture the temperature increases throughout
process because composition of vapor changes continuously.

27. Contd….
Types of Distillation
• Simple Distillation
• Fractional Distillation
• Steam Distillation
• Vacuum Distillation
• Destructive Distillation

28. Contd….
1- Simple Distillation
• Simple distillation is a process of converting a liquid into its vapors,
transferring the vapors to another place, and recovering the liquid by
condensing the vapors, usually by leading contact with a cold surface.
The apparatus used consists of 3 parts;
• Still in which volatile material is vaporized.
• Condenser in which vapors are condensed.
• Receiver in which distillate is collected.

29. Contd….
• Simple distillation can produce partial separation of components with
different boiling points in a liquid mixture.
• The process is generally used for separation of liquids from non-
volatile solids, e.g., preparation of distilled water and recovery of
alcohol in the preparation of dry extracts.
• Simple distillation is practiced for a mixture in which the boiling
points of the components differ by at least 70°C.
• It is also followed for the mixtures contaminated with nonvolatile
particles (solid or oil) and those that are nearly pure with less than 10
percent contamination

30. Contd….
Double distillation is the process of repeating distillation on the
collected liquid in order to enhance the purity of the separated
compounds.
Process of Simple Distillation
• For simple distillation on laboratory scale, a distillation flask with side
arm slopping downwards is used
• The temperature at which the vapors distil is observed on a
thermometer
• Thermometer is inserted through a cork and having its bulb just
below the level of the side arm.

31. Contd….
• The size of the flask should be good enough to hold the volume
double than the required volume .
• Bumping, due to heating is avoided by adding a small chip of porous
pot before the start of distillation in the flask.
• If the process is interrupted, a fresh chip should be added. They will
prevent superheating of the liquid being distilled and they will cause a
more controlled boil, eliminating the possibility that the liquid in the
distillation flask will bump into the condenser.
• Chips should not be added to the superheated liquid; otherwise an
instantaneous evolution of a large volume of vapors will occur.

32. Contd…..

33. Contd….
Condenser
• A condenser is a heat exchanger; its surface is kept cold by a stream of cold water.
It should have the following properties;
1. Construction of condenser should be such that it can be easily cleaned.
2. The broken parts may be easily replaced so that the cost of new one is saved.
3. Provide maximum cooling surface because the rate of condensation is directly
proportional to the cooling area.
4. Condensing surface should be good conductor of heat, therefore where
practicable metal condensers are preferred over glass.
5. Water used for cooling must leave the condenser quickly so as to provide space
for water to get in and provide cold surface.
6. Water must flow in opposite direction to vapors so that the condensed liquid
should leave the condenser in as cool a condition as possible.

34. Contd ….
• Limitations of Simple Distilllation
• It produces a distillate that is always impure at any temperature range
between the ranges of boiling points of the components. Therefore, it
is impossible to completely separate the components in a mixture
with Simple Distillation.
• Relatively pure substances can be obtained from a mixture with
Simple Distillation if the boiling points of the components differ by a
large amount (>70ºC).
• This may be a very tedious process involving a large number of
distillations.

35. Contd….
Properties of Simple Distillation
• Simple set up.
• Fast process.
• Consumes less energy.
• Poor separation.
• Best for relatively pure liquids.
•
Applications of Simple Distillation
• For purification of organic liquids.
• Separation of liquids from non-volatile solids – recovery of alcohol in the preparation of
dry extracts.
• Preparation of different substances – ether amyl nitrate etc.
• Preparation of distilled water.
• Identification.

36. Contd….
2. Fractional Distillation
Introduction :
• Simple Distillation separates components of a mixture based on the
differences in boiling points of the pure components.
• The closer the boiling points are to each other, the more difficult the
separation , hence Fractional Distillation is used instead of simple
distillation .
• The boiling point of a substance determined by distillation is a useful
physical property for the characterization of pure compounds

37. Contd…..
• Fractional Distillation is one of the most common separation method
used when purifying liquid organic samples.
• especially to separate miscible volatile liquids having different boiling
points e.g.., mixture of Alcohol and water.
• It is quite easy to separate a liquid from non-volatile solids by simple
distillation but it is very difficult to separate two volatile liquids
completely from each other by simple distillation.
• The fractional Distillation accomplishes the same Condensation
Cycles, by inserting a Fractionating Column between the Distillation
Flask and the Distillation Head.

38. Contd….
• The Fractionating Column subjects the mixture to many Condensation
Cycles as the material moves up the column toward the Distillation
Head. With each cycle within the column, the composition of the
vapor is progressively enriched in the lower boiling liquid. This
process continues until most of the lower boiling compound is
removed from the original mixture and condensed in the receiving
flask.

39. Contd….
Process
• Distillation is one of the oldest and still most common methods for
both the purification and the identification of organic liquids. It is a
physical process used to separate chemicals from a mixture by the
difference in how easily they vaporize. As the mixture is heated, the
temperature rises until it reaches the temperature of the lowest
boiling substance in the mixture, while the other components of the
mixture remain in their original phase in the mixture. The resultant
hot vapor passes into a condenser and is converted to the liquid,
which is then collected in a receiver flask.

40. Contd….
• When the lower boiling liquid is effectively removed from the original
mixture, the temperature rises and a second fraction containing some
of both compounds is produced. As the temperature approaches the
boiling point of the higher boiling point compound, the distillate
condensing into the third receiving flask is increasingly pure in the
higher boiling point compound

41. Contd…
Principle
• The principle of fractional distillation is based on the establishment of a large
number of theoretical vaporization-condensation cycles .
• The apparatus of a simple distillation is modified by inserting a fractionating
column between the distillation flask and the distillation head.
• The fractionating column provides a large surface area in which the initial
distillate is redistilled and condensed again.
• This process continues as the vapors rise up the column until the vapors finally
make it into the condenser.
• These vapors and the final distillate will contain a greater percentage of the lower
boiling liquid.
• Continuous repetition of re distillation process in fractional distillation gives good
separation of the volatile liquid components.

42. Contd…

43. Contd…
Azeotropic mixtures
• Azeotropic mixture or constant boiling mixture is one in which the
composition of the liquid and the vapor in equilibrium with it, is the same.
• Their proportions cannot be altered by simple distillation.
• The mixture behaves like a pure liquid and distils without change in
composition or boiling point. Such mixtures cannot be separated into their
pure components by simple distillation, e.g., alcohol and water, alcohol and
benzene, alcohol and chloroform.
Ternary mixtures
• Mixtures of three components, which do not form azeotropes may be
separated by fractional distillation in the same way as the binary mixtures.

44. Contd…
Properties of Fractional Distillation
• complicated
• slow
• Consumes more energy
• better separation
• Best for mixtures with close B.P
Applications of Fractional Distillation
• Separation of two immiscible liquids having different boiling points.
• Separation of ternary mixtures.
• Manufacture of Alcohol

45. Contd….
3. Steam Distillation
Introduction :
• Steam distillation is a special type of distillation for temperature sensitive
materials like natural aromatic compounds.
• Many organic compounds tend to decompose at high sustained
temperatures. Separation by normal distillation would then not be an
option, so water or steam is introduced into the distillation apparatus
• By adding water or steam, the boiling points of the compounds are
depressed, allowing them to evaporate at lower temperatures, preferably
below the temperatures at which the deterioration of the material
becomes appreciable

46. Contd….
• Steam distillation is used for the distillation of water-immiscible
liquids of high boiling points, e.g., turpentine, aniline.
• By bubbling steam through the liquid, the mixture boils at below the
normal boiling point of the either component.
• The distillate consists of the two liquids in the same proportions as in
the vapor E.g. Turpentine has a boiling point of 160 C, when mixed
with water it can be distilled at about 95.6C.

47. Contd…
Steam Distillation Principle
This method is based on the fact that, total vapor pressure above a
mixture of two immiscible liquids is equal to the sum of the vapor
pressures of the individual liquids i.e,
Ptotal = P1 + P2 Hence, P2 = Ptotal - P1
A liquid boils at the temperature when its vapor pressure becomes
equal to the atmospheric pressure.
Steam is continuously passed over the impure organic liquid; the
steam heats the liquid and gets condensed into water itself.
The resulting mixture of liquid and water begins to boil when the
vapor pressure above the mixture becomes equal to the atmospheric
pressure.

48. Contd…
• Hence the mixture of the two immiscible liquids will boil at a
temperature lower than the normal boiling points of both the liquids.
• The mixture will continue to boil at the same temperature until one
of the liquids is completely distilled out.
• The distillate, which contains water and the liquid, separates out into
two layers as both are immiscible with each other.
• The two layers can be separated using a separating funnel.

49. Contd….
Steam Distillation Process
• The impure compound and water are placed in a distillation flask kept
at a slight slant position and heated on a sand bath.
• Steam is then bubbled through this mixture.
• The vapors of the compound, along with steam, leave the flask from
the outlet and get condensed in the water condenser.
• The condensate collected in the receiver is transferred to a separating
funnel.
• The liquid compound being immiscible with water forms a separate
layer and can be separated.

50. Contd….
Solid Drying Agents
• Final traces of water are removed by treating the organic solution with a
drying agent.
• A drying agent is an inorganic salt which readily takes up water to become
hydrated.
• Several such salts are used routinely in labs. Magnesium sulphate is a good
general choice as it is fast and not very soluble in water.
• There is no set “rule” as to how much drying agent needs to be added. The
amount required depends on the amount of water in the liquid or solvent
solution which you are drying. This amount varies from experiment to
experiment.

51. Contd….
• Use as much as it takes to dry the solution. In most cases, drying is
complete in 20 minutes.
• When drying is complete, you need to remove the dried organic
solution from the drying agent. There are several methods by which it
can be done.
• If the powder is quite fine (as when using magnesium sulphate) or if
the volume is large, gravity filtration is the method of choice.
• In case the drying agent is of larger particle size (as when using
sodium sulphate or calcium chloride, decanting is the method of
choice.

52. Contd….
Small Scale Steam Distillation
• On laboratory scale the apparatus consists of a steam generator fitted with
a rubber bung/plug having two holes.
• Through one hole a long safety tube is passed which permits the expulsion
of some water if excessive pressure is generated inside the steam
generator.
• Through the second hole, a bent tube is passed which carries the steam to
the flask containing the liquids to be distilled (immicible liquid + water).
• The bent tube must dip almost to the bottom of the flask.

53. Contd…..
• The steam must touch below the surface of the liquid, and heat it up.
So that a rapid current of steam passes through the boiling mixture in
the flask.
• The vapors are allowed to pass through the condenser and the
condensed liquid is collected in the Florentine receiver.

54. Contd….

55. Contd….
Florentine Flasks
• The distillate which forms in two layers – one aqueous and the other
non-aqueous , are separated from each other as completely as
possible. For separation Florentine receivers or separating funnel is
used. Florentine receiver is a specialized receiver for collecting the oil
and water in the same receiver.

56. Contd….
Applications
• For distillation of water immiscible liquids of high boiling points –
turpentine, aniline, phenylalanine etc.
• For extraction of volatile oils from their crude drugs – clove oil, anise
oil and Eucalyptus oil from clove, anise and Eucalyptus.
• For purification of volatile substances.
• In the manufacture of essential oils, for use in perfumes.
• To separate intermediate or final products during the synthesis of
complex organic compounds.

57. Contd….
4- Vacuum Distillation
• Vacuum distillation is also known as distillation under reduced
pressure.
• It works on the principle that a liquid boils when its vapor pressure is
equal to the atmospheric pressure or the external pressure.
• This technique is used for purifying or separating thermally unstable
liquid compounds that decompose at their normal boiling points.
• Liquids which are unstable at their boiling points can be distilled at a
much lower temperature than their boiling points, under reduced
pressure with less likelihood of decomposition.

58. Contd….
• Boiling under reduced pressure also increases the rate of distillation.
• Under this condition, the compounds boil below their normal boiling
temperature. Hence, vacuum distillation is best suited for separation of
compounds with higher boiling points (more than 200°C), which tend to
decompose at their boiling temperature.
Vacuum Distillation Principle
• The lowering of pressure on the surface of a liquid lowers its boiling point.
As a result of this, a liquid can be boiled and distilled, without any
decomposition, at temperature much below its normal boiling point.
Distillation under reduced pressure or vacuum is carried out in a specially
designed glass apparatus. A two necked 'Claisen's flask' is used.

59. Contd….

60. Contd….
Process
• Distillation under reduced pressure is very commonly used for the
evaporation of the menstrum in the preparation of the extracts.
• Vacuum distillation is most conveniently carried out in a specially
designed flask, known as Claisen flask
• This special flask has two necks. Through one neck, a thermometer is
inserted and is attached to the condenser. Through the other neck a
very fine capillary tube is introduced which completely dips in the
boiling liquid.

61. Contd….
• Bumping readily occurs during the distillation under reduced
pressure, but it can be easily prevented by introducing stream of air
bubbles passing into the liquid, through the fine capillary tube
• The capillary tube should be sufficiently fine to permit only a slow
stream of bubbles to be blown into the tube.
• The side tube of the receiver is connected to a vacuum pump to
provide the suitable vacuum

62. Contd….
• In all vacuum distillations, a small pressure gauge (manometer)
should be inserted between the receiver and the vacuum pump
• In carrying out the distillation, heating is not commenced until the
required vacuum has been attained above the surface of the liquid,
otherwise frothing of the hot liquid will result in the receiver.
• Heating of the flask should be done on a water bath or oil bath
maintained at about 20ºC higher than the boiling point of the liquid
under reduced pressure.

63. Contd….
• Thin walled glass apparatuses, such as ordinary flat bottomed flasks
and conical flasks should never be used for vacuum distillation;
otherwise collapsing of such apparatus may result.
• In some cases, persistent foaming occurs during the process of
vacuum distillation. This may be overcome by adding capryl alcohol to
the liquid to be distilled, or by inserting a second air capillary tube in
the thermometer neck of the claisen flask. The stream of air drawn
through the tube breaks the rising foam.

64. Contd….
Vacuum Distillation Advantages
• The compounds that decompose on heating to their boiling points can be
purified by distillation under reduced pressure. This is because at the
reduced pressure, a liquid would boil at a temperature much below its
normal boiling point.
• Distillation under reduced pressure is more fuel-economical as it makes the
liquid boil at temperatures well below the normal boiling point.
• Vacuum distillation is used to safely recover higher boiling point solvents.
• It is used to safely recover solvents with boiling points over 300º
Fahrenheit.
• Vacuum distillation should not be used on solvents with boiling points
below 200º Fahrenheit.

65. Contd….
Applications
• For distillation of thermo labile substances.
• For concentration and drying of extracts which get destroyed at high
temperature.
• Vitamins.

66. Contd….
5- Destructive distillation
• Destructive distillation is the term used to describe the
decomposition of a substance, usually a natural product, by heat
followed by the condensation and collection of the volatile products
of decomposition.
• It is not a pharmaceutical process but is used in the manufacture of
some substances used in medicines.

67. 4. Vaporization
Introduction .
• Vaporization of an element or compound is a phase transition from
the liquid to gas phase
• There are two types of vaporization -- evaporation and boiling
• Evaporation is a phase transition from the liquid phase to gas phase
that occurs at temperatures below the boiling temperature at a given
pressure.
• Evaporation usually occurs on the surface.

68. Contd….
• Boiling is a phase transition from the liquid phase to gas phase that
occurs at or above the boiling temperature.
• Boiling, as opposed to evaporation, does not occur only at the
surface.
• Sublimation on the other hand is a direct phase transition from the
solid phase to the gas phase, skipping the intermediate liquid phase.
• Heat must be supplied to a solid or liquid to effect vaporization.
• If the surroundings do not supply enough heat, it may come from the
system itself as a reduction in temperature.

69. Contd….
• The atoms or molecules of a liquid are held together by cohesive
forces, and these forces must be overcome in separating the atoms or
molecules to form the vapour.
• The heat of vaporization is a direct measure of these cohesive forces
• Condensation of a vapour to form a liquid or a solid is the reverse of
vaporization
• In condensation heat must be transferred from the condensing
vapour to the surroundings. The amount of this heat is the same as
the heat of vaporization.

70. Contd….
Applications :
• Coating of Tablets .
• Control of Moisture Content of Powders
• Drying of wet granules , to be used in compression of tablets .

71. 5. Evaporation .
Introduction :
• Evaporation is a type of vaporization of a liquid that occurs only on
the surface of a liquid.
• The other type of vaporization is boiling, which instead occurs on the
entire mass of the liquid
• Theoretically evaporation means free escape of vapours from the
surface of a liquid below its boiling point.
• As evaporation is a very slow process, therefore a liquid is usually
boiled / heated to speed up this process.

72. Contd….
• So, practically evaporation may be defined as the removal of liquid
from a solution, by boiling the solution in a suitable vessel from
where the vapors are withdrawn and a concentrated liquid is left
behind.
• The Evaporation is maximum at the boiling point of a substance.
• For molecules of a liquid to evaporate, they must 1)be located near
the surface,2) be moving in the proper direction, and 3)have
sufficient kinetic energy to overcome liquid-phase intermolecular
forces

73. Contd….
• Only a small proportion of the molecules meet these criteria, so the
rate of evaporation is limited.
• Since the kinetic energy of a molecule is proportional to its
temperature, evaporation proceeds more quickly at higher
temperatures.
• As the faster-moving molecules escape, the remaining molecules
have lower average kinetic energy, and the temperature of the liquid,
thus, decreases.

74. Contd….
Factors Effecting Evaporation .
• Temperature
• Surface Area
• Agitation
• Atmospheric Aq Vapor Pressure
• Type of Product required
• Economic Factors

75. Contd….
1) Temperature
The rate of evaporation is directly proportional to the temperature.
The higher the temperature, the higher will be evaporation but
evaporation is maximum at the boiling point of the liquid.
2) Surface Area
The rate of evaporation is directly proportional to the surface area of
the vessel exposed to evaporation. Greater the surface exposed to
evaporation, the higher will be the rate of evaporation.

76. Contd….
3) Agitation
During evaporation a layer or scum is formed at the surface. Therefore
it is necessary to agitate and stir the solution during evaporation.
Agitation also increases the rate of evaporation .
4) Atmospheric aqueous vapor pressure
If atmospheric moisture contents in air are high, rate of evaporation
will be slow but if less then evaporation will be fast. Rate of
evaporation can be increased by circulation of warm air over the
evaporating pan.

77. Contd….
5) Atmospheric Pressure
Rate of evaporation is inversely proportional to the atmospheric pressure on
the surface of the liquid. Rate of evaporation become doubled by reducing
the atmospheric pressure on the liquid to one half. Due to this reason , in
many cases evaporation is done under reduced pressure.
6) Type of the product required
Selection of method and apparatus depends on the type of the product
required.
7) Economic factors
They contribute significantly in selecting the method and the type of
apparatus to be used for evaporation.

78. Contd….
Types of Evaporators
1. Small Scale Evaporators
2. Large Scale Methods
a) Evaporating Pans
b) Evaporating Stills

79. Contd…
1. Small Scale Evaporators (Lab Scale )
• Small quantity of liquids may be evaporated in porcelain or glass dish.
• Direct heat by Bunsen burner or electric hot plate may be applied,
but direct heat leads to decomposition of the substances towards the
end of the evaporation
• A fixed maximum temperature can easily be attained by employing
different types of baths as a source of indirect heating
• Water bath is most suitable when liquids are to be heated up to
100ºC. These are simple and cheap

80. Contd….
• Sand bath or oil bath containing liquid paraffin or soft paraffin may be
used when higher temperatures upto 300ºC are required.
• Glycerin bath is used to attain a temperature upto 150ºC
• To prevent decomposition, whole of the liquid should not be
evaporated to dryness; instead the last traces of the solvent from the
concentrated liquid should be removed under controlled
temperature.
• In case of large quantities of liquids or solutions having costly
solvents, the evaporation should be carried out by distillation under
reduced pressure.

81. Contd….
2- Large scale methods
(a) - Evaporating pans
• On large scale, liquid extracts containing water as a menstruum are
evaporated in large open pans called evaporating pans.
• They consist of hemispherical or shallow pans, made of copper,
stainless steel, aluminum, enameled iron or other metal and
surrounded by a steam jacket.

82. Contd….

83. Contd….
• The hemispherical shape is most suitable because it gives the best
surface/volume ratio for heating and the largest area for
disengagement of vapours.
• The pans may be fixed, or have a mounting, permitting it to be tilted
to remove the product.

84. Contd….
• Advantages
1.They are simple, easy and cheap to construct.
2.Easy to use, clean and maintain.
3.Stirring of the evaporating liquid can easily be done.
• Disadvantages
1.On the evaporating surface a scum is rapidly formed which decreases rate of
evaporation.
2.Solids may be deposited at the bottom, which makes stirring necessary.
3.Cannot be used for extracts containing organic solvents like alcohol etc.
4.The rooms, in which the evaporating pans are used, must have an efficient
exhaust system. Otherwise the room will be filled with dense fog of condensed
vapors and water will start falling from the roof and along the sides of the wall

85. Contd….
(b) - Evaporating stills
• These are similar to pans, and consist of a vessel made of copper or
stainless steel .
• They are used in large scale pharmaceutical manufacturing
Applications of Evaporation :
1.One of the most important method in manufacture of
pharmaceuticals.
2.Used for preparation of different type of extracts.
3.In the manufacture of drugs containing antibiotics, hormones,
enzymes etc.

86. 6. Dessication
General Introduction :
• Desiccation is the state of extreme dryness, or the process of extreme
drying.
• A desiccant is a hygroscopic substance ,that induces or sustains such a
state (Dryness) in its local vicinity ,in a moderately sealed container.
• A desiccator is a heavy glass or plastic container used for making or
keeping small amounts of material very dry.

87. Contd…..
• The material is placed on a shelf, and a drying agent or desiccant,
such as dry silica gel or anhydrous sodium hydroxide, is placed below
the shelf.

88. Contd…..
• Desiccation is the process of removing adhered moisture from liquid or
solid substances.
• The term desiccated is used for those substances from which the water or
moisture has been completely removed.
Process:
• On small scale, desiccation can be carried out in a desiccator which consists
of a tightly closed glass or plastic vessel , containing a drying agent at its
bottom, which absorbs the moisture from the substance being desiccated.
• Commonly used desiccants are, conc. Sulphuric acid, phosphorus
pentoxide, exsiccated calcium chloride and silica gel.
•

89. Contd…..
• The drug or substance to be dried is taken in a china dish and placed
inside the desiccator above the surface of drying agent .
• For continuous operation the desiccator may sometimes be
connected to a vacuum pump.
• The moisture sensitive substances formulated in tablets and capsules
are protected by enclosing them in sealed vials, on bottom of which a
small cloth bag containing silica gel is placed which acts as a
desiccant.
• In case of organic solvents, the traces of moisture are removed by
passing them through a column of alumina or silica gel.

90. Contd…..
Applications
• In preservation of vegetable and animal drugs that are destroyed in
presence of moisture.
• Comminution of drugs is difficult when they are wet, but it becomes
easy when they are dried.
• To decrease the bulk and weight of substances containing moisture to
facilitate their easy handling.
• To increase the stability of drugs.

91. 7. Levigation
General Introduction :
• Levigation is commonly used in small scale preparation of ointments
to reduce the particle size and grittiness of the added powders.
• A mortar and pestle or an ointment tile is used for this purpose.
• A paste is formed by combining the powder and a small amount of
liquid (the levigating agent) in which the powder is insoluble
• The paste is then triturated in the mortar by the pestle or on the
ointment tile by a spatula to reduce the particle size.

92. Contd…..
• The levigated paste is then added to the ointment base and the
mixture is made uniform and smooth by rubbing it together with a
spatula on the ointment tile.
• The most common levigating agents are mineral oil, water, alcohol
and glycerin.
• The process of levigation is also known as wet grinding and is used to
reduce the particle size of a substance to finer state of subdivision
• This process is often used to incorporate solid substances into
dermatological and ophthalmic ointments and suspensions.

93. Contd…..
Applications
1. Size reduction.
2. Preparation of ointments.

94. 8. Trituration
• Trituration may be used both to comminute and to mix powders.
• By trituration the grinding of a solid substance is done to fine powder
by continuous striking or rubbing the particles in a mortar with a
pestle.
• If simple admixture is required without special need for comminution,
the glass mortar is usually preferred.
• When a small amount of a potent substance is to be mixed with a
large amount of diluent, geometric dilution method is used to ensure
the uniform distribution of the potent drug.

95. Contd…..
• This method is specially indicated when the potent and other ingredients
are of the same color and a visible sign of mixing is lacking. By this method
the potent drug is placed on an approximately equal volume of the diluent
in the mortar and mixed thoroughly by trituration. Then a second portion
of diluent equal in volume to the mixture is added and the trituration
repeated and so on. This process is repeated until all the diluent is
incorporated.
Applications
1. Size reduction.
2. Geometric mixing of powders.

96. 9.Efflorescence
• Efflorescence is the loss of water of crystallization from a hydrated salt to
the atmosphere on exposure to air.
• The hydrated substances under normal conditions exert vapor pressure due
to their water of crystallization.
• HYDRATES: Solids that contain water molecules as part of their crystalline
structure.
• The water in the hydrate is known as the water of hydration or the water of
crystallization.
• The combination of water molecules with molecules of a compound results
in a hydrate.

97. Contd…..
• A large number of compounds crystallize in hydrated form. e.g.,
CuSO4 combines with 5 molecules of water.
Na2SO4 combines with 10 molecules of water.
MgSO4 combines with 7 molecules of water.
FeSO4 combines with 7 molecules of water.
• Presence of water of crystallization is not essential for crystal
structure, as Sodium chloride, potassium nitrate and many other
compounds have definite crystal structures without water of
crystallization.

98. Contd…..
Principle
• If the vapor pressure of a hydrated salt is greater than the pressure
exerted by the water vapors in the surrounding atmosphere then the
salt will tempt to attain equilibrium with its surroundings, and will
therefore tend to lose water to form a lower hydrate or an anhydrous
salt.
• This phenomenon is called as Efflorescence

99. Contd…..
• For example, the vapor pressure of washing soda (Na2CO3•10H2O)
normally exceeds that of the water vapor in the atmosphere, these
salts effloresce (i.e., lose all or part of their water of hydration), and
their surfaces assume a powdery appearance.
• . Hydrated cupric sulfate, or blue vitriol (CuSO4•5H2O), the aqueous
vapor pressure of which is lower, undergoes efflorescence only if the
air in contact with it is relatively dry

100. Contd…..
• A salt such as copper sulfate may form more than one hydrate, each
of which possesses its own definite vapor pressure at a given
temperature. The following hydrates of copper sulfate are known:
CuSO4 . 5 H2O, CuSO4 . 3 H2O and CuSO4 . H2O
• When certain substances of low vapor pressure, such as CaCl2 . H2O,
are exposed to air, they form higher hydrates. Such salts may be used
in the removal of moisture from air or other gases.

101. Contd…..
Example
• Pressure of water vapor in the atmosphere is about 13.3X10² N/m² at
293 k.
• Therefore the hydrates with vapor pressure greater than this will
show efflorescence and will be unstable, provided that the lower
hydrate formed still exerts a vapor pressure greater than the
surrounding atmosphere.
• If this is not so, the water will be taken up from the atmosphere by
the lower hydrate as fast as it is formed and the final equilibrium will
depend on the rates at which water is lost or taken up by the two
hydrates.

102. Contd…..
• E.g. The behavior of various forms of sodium carbonate.
Na2CO3.10 H2O (V.P = 32X10² N/m²)
Na2CO3.H2O (V.P = 16X10² N/m²)
Na2CO3 (anhydrous) (V.P = 0)

103. Contd…..
• The Vapor pressure exerted by the Decahydrate is much greater than
that of normal atmosphere and it loses water by efflorescence and is
converted to monohydrate.
• The vapor pressure of it is still above that of atmosphere, but further
apparent loss of water does not occur because the anhydrous salt is
rehydrated at a faster rate than dehydration of the monohydrate.
• The vapor pressure of hydrated salts, and therefore the rate of
efflorescence increases with rise in temperature

104. 10- Exsiccation
• It is the process of accelerating the rate of efflorescence by increasing
the temperature in order to remove the water of crystallization from
a hydrated salt .
• It may be regarded as process of Efflorescence, controlled and
accelerated, but is applied in cases where water is not normally lost
by efflorescence.

105. Contd….
Process:
• Exsiccation may be carried out by taking a weighed amount of the
substance in a tarred dish (weight of dish is subtracted from the
weight of substance, or dish is auto-zeroed)
• It is then heated on a water bath, sand bath or in an oven with
continuous stirring until a constant weight is obtained and there is no
further loss in weight.
• No further loss in weight indicates that exsiccation has been
completed and no further water loss can take place
• Mostly a sand-bath or air oven is used for this process.

106. Contd….
• The principles involved in the process of exsiccation are the same as
those in the process of efflorescence.
• The temperature required to remove the water of crystallization is
very important and varies widely.
• For example in CuSO4.5H2O, when heated at 30°C loses two
molecules of water of crystallization forming CuSO4.3H2O
• At 100°C it loses two more water molecules resulting in CuSO4.H2O
• The last water molecule is removed at 200°C thus forming anhydrous
CuSO4.

107. Contd….
• Some exsiccated substances are not necessarily anhydrous.
• For example Ferrous sulphate (FeSO4.7H2O) when heated at about
100-105°C loses 6 molecules of water of crystallization .
• When further heated to remove the last water molecule, its
decomposition takes place.
• Hence, FeSO4.H2O is called exsiccated ferrous sulphate.

108. Contd….
• If its exsiccation is carried out under vacuum then anhydrous
FeSO4can be obtained below 100°C.
• The examples of exsiccated salts used in pharmacy are exsiccated
ferrous sulphate, exsiccated copper sulphate, exsiccated sodium
sulphate, exsiccated magnesium sulphate, exsiccated sodium
carbonate, exsiccated sodium phosphate and exsiccated alum etc.
• As the exsiccated salts are very hygroscopic, they must be stored in
air-tight containers.

109. Contd….
Applications
• Exsiccation is carried out to get an anhydrous product required in the
formulation of pharmaceuticals. .
• After the removal of water the bulk and weight of the drug is reduced
and they can be easily administered/used in manufacturing.
• Potency of drug is increased after the removal of water.
• After exsiccation fine powder is obtained which is easy to handle.

110. 11- Deliquescence
• HYGROSCOPIC: A substance is hygroscopic if it readily absorbs water
from the atmosphere and forms a hydrate.
• DELIQUESCENT: A substance is deliquescent if it absorbs water from
the air until it forms a solution.
• Both these terms are used to indicate that a material takes up water
vapors from the atmosphere and is converted to a more hydrated
form. In case of hygroscopic substance, the more hydrated state is till
a solid but in deliquescence there is eventual formation of a liquid
phase i.e., a solution.

111. Contd…..
• Such substances are said to be DELIQUESCENT, and the process is
termed DELIQUESCENCE.
• Very soluble salts, such as CaCl2 are often extremely deliquescent.
• In both phenomena, the final more hydrated state must still exert a
lower vapor pressure than that of the water vapor in the surrounding
atmosphere. Otherwise the newly formed hydrated state will
immediately lose water by efflorescence and revert to the initial state

112. Contd…..
• Thus for a liquid phase to be produced by deliquescence, it is
necessary that the V.P. exerted by the saturated solution of the
deliquescent material should be less than that of the surrounding
atmosphere.
• Deliquescent materials are substances (mostly salts) that have a
strong affinity for moisture and will absorb relatively large amounts of
water from the atmosphere if exposed to it, forming a liquid solution

113. Contd…..
• Deliquescent salts include calcium chloride, magnesium chloride, zinc
chloride, potassium carbonate, potassium phosphate, potassium
hydroxide, and sodium hydroxide.
• Examples of hygroscopic materials include, exsiccated sodium sulphate,
ammonium chloride etc.
• For Hygroscopic and deliquescent pharmaceutical preparations specialized
storage conditions are required.
Applications :
• Owing to their very high affinity for water, these substances are often used
as desiccants; these compounds are used in the chemical industry to
remove the water produced by chemical reactions.

114. 12 Fusion
• It is the process by which the solids get converted into liquids without
the addition of any solvent.
• In other words it is defined as the process of heating the solids until
they melt.
• In a pure crystalline solid, this process occurs at a fixed temperature
called the melting point
• An impure solid generally melts over a range of temperatures below
the melting point of the principal component.

115. Contd…
• Amorphous (non-crystalline) substances such as glass melt by
gradually decreasing in viscosity as temperature is raised, with no
sharp transition from solid to liquid.
• The structure of a liquid is always less ordered than that of the
crystalline solid and, therefore, the liquid commonly occupies a larger
volume
• Thermal fusion of a given mass of a solid requires the addition of a
characteristic amount of heat, the heat of fusion

116. Contd…
• In the reverse process, the freezing of the liquid to form the solid, the
same quantity of heat must be removed.
• The heat of fusion of ice, the heat required to melt one gram, is about
80 calories; this amount of heat would raise the temperature of a
gram of liquid water from the freezing point (0° C, or 32° F) to 80° C
(176° F).

117. Contd…
Applications
• Fusion is done to purify certain solid and semisolid substances e.g.,
substances like Bees wax, hard paraffin, soft paraffin and wool fat are
heated to melt and filtered while hot to remove the dissolved impurities.
Then cooling is done to obtain a product free from dissolved impurities.
• This method is also applied for the preparation of ointments when they
contain solids and semisolids in the formulation. All the substances are first
molted and then cooled slowly with constant stirring until a uniform
product is obtained. To avoid overheating, the substances with higher
melting points are melted first to which substances with lower melting
points are added.

118. • 13. Crystallization
• 14. Lyophillization
• 15 Adsorption
• 16. Sublimation
• 17 Elutriation
• 18. Calcination
• 19 Decantation
The above listed topics have been covered in class presentations
assigned to students .