Category Archives: Third semester
PRACTICAL – DETERMINATION OF HLB NUMBER (HYDROPHILLICLYPOPHILLIC BALANCE)
Object – To determine the HLB number (HydrophillicLipophillic Balance number) of a surfactant by saponification method.
Reference – Mohanta G.P. & Manna P.K., Physical pharmacy – Practical Text, Pharma Book Syndicate, Hyderabad, 2006, 3033
Materials required –
Chemicals – polyoxyethylene sorbitan monolaurate (Tween 20), alcoholic potassium hydroxide (2.82%), phenolphthalein, lauric acid, standard N/2 hydrochloric acid, standard N/10 Potassium hydroxide, alcohol, ether.
Glasswares & Apparatus – round bottom flask, condenser, waterbath, burette, burette stand, pipette, beaker, measuring cylinder, conical flask
Theory – The hydrophiliclipophillic balance (HLB) of a surfactant is a measure of its polarity. The HLB value of nonionic surfactant can be calculated using the formula –
HLB = 20 (1S/A)
Where S= Saponification number of ester and A = Acid number of fatty acid.
Saponification number is defined as number of milligram of potassium hydroxide required to neutralize the acid present in one gram of substance.
Acid number is defined as the number of milligram of potassium hydroxide required to neutralize the free acid present in one gram of substance.
The normal values of tween 20 (polyethelene sorbitan monolaurate) are Saponification number (S) = 45.5, Acid number (A) = 276 and HydrophillicLypophillic balance number (HLB) = 16.7
Procedure – Determination of saponiofication number – First of all, 1 gram of sample (Tween 20) was accurately weighed and taken in a round bottom flask. Then 30 ml of alcoholic potassium hydroxide (2.82%) was added and refluxed on boiling water bath for 1 hour. A blank experiment was performed in the same way but without sample. The reaction mixtures were cooled down to room temperature and titrated against standard N/2 hydrochloric acid using phenolphthalein as indicator taking color change from pink to colorless or slightly yellow as end point.
Determination of acid number – First of all, 500 milligram of lauric acid was accurately weighed and taken in a conical. Then 10 ml of alcohol and 10 ml ether were added. It was heated slightly to dissolve the lauric acid. The above mixture was titrated against standard N/10 potassium hydroxide using phenolphthalein as indicator.
Observation & Calculation – Saponification number
Weight of sample taken for saponification number determination = ……………. gram
Let the titre value of sample = V_{1} ml
Titre value of blank = V_{2} ml
(V_{2}V_{1}) ml of N/2 hydrochloric acid equivalent potassium hydroxide was required to neutralize the sample taken
(V_{2}V_{1}) ml of N/2 HCl = (V_{2}V_{1}) ml of N/2 KOH
1000 ml N KOH = 56000 x N/2 x V_{2}V_{1}/1000 mg KOH
Saponification number = 56000 x N/2 x V_{2}V_{1}/1000 whole divided by amount of sample in gram.
Acid number
Let the titre value of N/10 KOH = V_{3} ml
V_{3} ml of N/10 KOH was required to neutralize the free acid in taken sample
Acid number (A) =
V_{3} X Eq. weight of KOH / weight of sample taken in gram x normality of KOH / Weight of sample in gram
HLB = 20 X (1S/A)
Result – The HLB value of polyoxyethelene sorbitan monolaurate (Tween 20) was ……………..
PRACTICALPHARMACEUTICAL ENGINEERINGIFACTORS AFFECTING RATE OF EVAPORATION
Object – To see the effect of following factors on rate of evaporation –
 Concentration
 Surface area
 Thickness/Viscosity
Reference – Subrahmanyam C.V.S. etal, Laboratory manual of Pharmaceutical engineering – unit operations, Vallabh publications, Delhi, II edition, 2011, 116120.
Materials required –
Chemicals – Glycerine, sodium chloride
Glasswares and apparatus – Water bath, beaker, graph paper, measuring cylinder
Theory – Change of water to water vapor or liquid to vapor phase is called evaporation. Rate of evaporation is effected by many factors like surface area, concentration and thickness/viscosity. As surface area increases, the rate of evaporation increases because number of molecules are more for getting the heat. As concentration increases, the rate of evaporation decreases and as viscosity increases, the rate of evaporation decreases.
Procedure –
 Effect of concentration –
 Three beakers were taken of different capacity.
 25 ml water was taken in each beaker.
 All beakers were kept over boiling water bath for 30 minutes.
 After 30 minutes, the volume of water left was measured.
 Quantity of water evaporated was then calculated.
 Then rate of evaporation was calculated.
 Surface area of each beaker was calculated.
 A graph was plotted between rate of evaporation and surface area.
Observation –
S.NO.  BEAKER  RADIUS  VOLUME OF WATER TAKEN  VOLUME OF WATER LEFT AFTER HEATING  QUANTITY OF WATER EVAPORATED 
1  50 ml  2.0 cm  25 ml  
2  150 ml  2.75 cm  25 ml  
3  250 ml  3.25 cm  25 ml  
4  500 ml  4 cm  25 ml 
Calculation –
Rate of evaporation = Quantity of water evaporated / Time of heating in minutes.
Let for 50 ml beaker, amount of water evaporated = 1 ml, then rate of evaporation = 1/30 ml/min
Surface area of beaker = πr^{2}
 If radius is 2 cm for 50 ml beaker, then area = 3.14 x 2 x 2 = 12.56 sq.cm.
 If radius is 2.75 cm for 150 ml beaker, then area = 3.14 x 2.75 x 2.75 = 23.74 sq.cm.
 If radius is 3.25 cm for 250 ml beaker, then area = 3.14 x 3.25 x 3.25 = 33.16 sq.cm.
 If radius is 4 cm for 500 ml beaker, then area = 3.14 x 4 x 4 = 50.24 sq.cm.
 Effect of Thickness/Viscosity
 In same capacity beakers, solutions of different ratios of glycerine and water were prepared as given below
S.NO.  GLYCERINE  WATER  CONCENTRATION 
1  5  45  10% 
2  10  40  20% 
3  15  35  30% 
4  20  30  40% 
 The above solutions were kept on boiling water bath for 30 minutes.
 After 30 minutes, volume of water left in all the beakers were measured.
 Quantity of water evaporated was then calculated.
 Then rate of evaporation was calculated.
 A graph was plotted between rate of evaporation and viscosity.
Observation –
S.NO.  TYPE OF SOLUTION  VOLUME OF SOLUTION  VOLUME OF WATER LEFT AFTER HEATING  QUANTITY OF WATER EVAPORATED 
1  10%  50 ml  
2  20%  50 ml  
3  30%  50 ml  
4  40%  50 ml 
Calculation –
Rate of evaporation = Quantity of water evaporated / Time of heating in minutes.
 Effect of concentration –
 In same capacity beakers, sodium chloride solution of different concentrations were prepared as given below
S.NO.  SODIUM CHLORIDE  WATER  CONCENTRATION 
1  5  100  5% 
2  10  100  10% 
3  15  100  15% 
4  20  100  20% 
 The above solutions were kept on boiling water bath for 30 minutes.
 After 30 minutes, volume of water left in all the beakers were measured.
 Quantity of water evaporated was then calculated.
 Then rate of evaporation was calculated.
 A graph was plotted between rate of evaporation and concentration.
Observation –
S.NO.  TYPE OF SOLUTION  VOLUME OF SOLUTION  VOLUME OF WATER LEFT AFTER HEATING  QUANTITY OF WATER EVAPORATED 
1  5%  100 ml  
2  10%  100 ml  
3  15%  100 ml  
4  20%  100 ml 
Calculation –
Rate of evaporation = Quantity of water evaporated / Time of heating in minutes.
Result – After performing the experiment, graphs were plotted. From the obtained graph, it was concluded that
 As surface area increases, rate of evaporation increases.
 As viscosity increases, rate of evaporation decreases.
 As concentration increases, rate of evaporation decreases.
PRACTICAL PHYSICAL PHARMACEUTICS – DETERMINATION OF SURFACE TENSION
Object – To determine the surface tension of given liquid by –
 Drop number method
 Drop count method
Reference – Bahl B.S. etal, Essentials of Physical chemistry, S.Chand & Company Limited, New Delhi, 24^{th} edition, 1997, 348352
Materials required –
Chemicals – Benzene or Toluene or ethyl alcohol or methyl alcohol
Glasswares & Apparatus – Measuring cylinder, Weighing balance, beaker, stalagmometer, weighing bottle
Theory – Surface tension arises on the surface of the liquid due to the intermolecular forces among the molecules of liquid. Molecules in the interior of the liquid is pulled in all directions equally but the molecules in the surface of the liquid is pulled in three direction only i.e. sidewards and downwards. This downward force pulls the molecules of the liquid to come inside which is called surface tension and this is the reason why a drop of water takes spherical shape. Hence, on this concept surface tension is defined as the force in dynes acting on the surface of liquid at right angles to a line 1 centimeter in length. In CGS system the unit of surface tension is dyne/cm and in SI system the unit of surface tension is Newton/meter. Stalagmometer is the apparatus which is used for the determination of surface tension.
Surface tension of some liquids at 20⁰C are –
LIQUIDS  SURFACE TENSION 
Water  72.75 
Ethyl alcohol  22.27 
Methyl alcohol  22.6 
Acetone  23.7 
Toluene  28.43 
Benzene  28.9 
Procedure –
 Drop number method
For sample liquid (1)
 A cleaned and dried stalagmometer was taken and it was filled with the sample liquid say toluene or benzene.
 20 drops of the sample liquid from the stalagmometer was taken in weighing bottle.
 Now the weighing bottle was weighed.
 From the obtained weight of 20 drops of sample liquid , weight of one drop of sample liquid (m_{1}) was calculated.
For reference liquid (2)
 A cleaned and dried stalagmometer was taken and it was filled with the sample liquid say toluene or benzene.
 20 drops of the sample liquid from the stalagmometer was taken in weighing bottle.
 Now the weighing bottle was weighed.
 From the obtained weight of 20 drops of sample liquid , weight of one drop of sample liquid (m_{2}) was calculated.
Observation table for sample liquid –
Weight of empty weighing bottle (a)  Weight of weighing bottle with the 20 drops of sample liquid (b)  Weight of 20 drops of sample liquid (c)= ba  Weight of one drop of sample liquid (m_{1})= c/20 

Observation table for reference liquid –
Weight of empty weighing bottle (a)  Weight of weighing bottle with the 20 drops of reference liquid (b)  Weight of 20 drops of reference liquid (c)= ba  Weight of one drop of reference liquid (m_{2}) = c/20 

Formula used to calculate surface tension
γ_{1 }m_{1}
_{ ——————— = ———————– } OR γ_{1 =} m_{1} γ_{2 / }m_{2}
γ_{2 }m_{2 }
_{ }where _{ }γ_{1 }= surface tension of sample liquid, γ_{2 }= surface tension of reference liquid, m_{1 }= weight of one drop of sample liquid and m_{2 }= weight of one drop of reference liquid_{ }
 Drop Count Method –
Procedure –
 First of all, a cleaned and dried stalagmometer was taken and it was filled with the sample liquid.
 Now the number of drops of sample liquid were counted from mark A to B.
 The same above steps were repeated for the reference liquid (water).
 Density of the sample liquid was determined by using the weighing bottle.
Observation table for density of sample liquid –
Weight of empty weighing bottle (a)  Weight of weighing bottle with sample liquid (b)  Weight of sample liquid (M)= ba  Volume of sample liquid (V) 

Observation table –
No. of drops of sample liquid (n_{1}) 

No. of drops of reference liquid (n_{2})

Calculation –
Density (d_{1}) = Mass / Volume = M / V =…………………..g/ml
Surface tension of sample liquid (γ_{1}) is calculated by using the formula –
γ_{1 / }γ_{2 }= n_{2}d_{1} / n_{1}d_{2}
Where γ_{1} = Surface tension of sample liquid, γ_{2 }= Surface tension of reference liquid (water = 72.75 dyne / cm), n_{1} = Number of drops of sample liquid, n_{2} = Number of drops of reference liquid, d_{1} = Density of sample liquid, d_{2} = Density of reference liquid (water = 1.0 g/ml)
Result – The surface tension of given sample liquid was carried out by drop weight method and drop count method and found ……………………. dyne /cm and ………………… ..dyne /cm respectively.