VISCOCITY OF SOLUTIONS || B.TECH FIRST YEAR CHEMISTRY PRACTICAL
Viscocity of Solutions
TITLE=Viscocity of solutions
OBJECT=Determination of percentage composition of sugar solution from viscocity using Ostwald Viscometer.
THEORY= The force of friction which one part of the liquid is called viscocity.For measuring viscocity coefficient, Ostwald viscometer method is used which is based on Poiseuille's law. According to this law ,the rate of flow of liquid through a capillary tube having viscocity coefficient η, can be expressed as
Where V=volume of liquid ( in ml)
t= flow time through capillary(in sec)
r= radius of capillary (in cm)
l= length of the capillary(in cm)
p= hydrostatic pressure (in dyne/sq cm)
η=viscocity coefficient (in poise)
Since ,the hydrostatic pressure (the driving force) of the liquid is given by p= dgh ( where h is the height of the column and d is the density of liquid);
η α pt or, η α dght
If,η1 and η2 are the viscocity coefficients of the liquids under study, d1,d2, are their densities and t1 and t2 are their times of flow of equal volume of liquids through the same capillary respectively,then.
η α d1ght1 and η2 α d2ght2
Hence, η1/η2=d1t1/d2t2
Here,usually the viscocity of given liquid is measured with respect to water whole viscocity is known very accurately at different temperatures.The SI physical unit of viscocity is the Pascal second (pa.s),(i.e,kg/m.s).This means if a fluid with a viscocity of one pa.s is placed between two plates ,and one plate is pushed sideways with a sheer stress of one pascal,it moves a distance equal to the thickness of the layerbetween the plates in one second. The cgs unit for the same is the poise (p).It is more commonly expressed ,as centipoise(cp).[1cp=0.001 pa.s].water at 20ºc has a viscocity of 1.0020cp.
OBSERVATION TABLE
RESULT = The percentage composition of unknown solution is 6.15%.
Where V=volume of liquid ( in ml)
t= flow time through capillary(in sec)
r= radius of capillary (in cm)
l= length of the capillary(in cm)
p= hydrostatic pressure (in dyne/sq cm)
η=viscocity coefficient (in poise)
Since ,the hydrostatic pressure (the driving force) of the liquid is given by p= dgh ( where h is the height of the column and d is the density of liquid);
η α pt or, η α dght
If,η1 and η2 are the viscocity coefficients of the liquids under study, d1,d2, are their densities and t1 and t2 are their times of flow of equal volume of liquids through the same capillary respectively,then.
η α d1ght1 and η2 α d2ght2
Hence, η1/η2=d1t1/d2t2
Here,usually the viscocity of given liquid is measured with respect to water whole viscocity is known very accurately at different temperatures.The SI physical unit of viscocity is the Pascal second (pa.s),(i.e,kg/m.s).This means if a fluid with a viscocity of one pa.s is placed between two plates ,and one plate is pushed sideways with a sheer stress of one pascal,it moves a distance equal to the thickness of the layerbetween the plates in one second. The cgs unit for the same is the poise (p).It is more commonly expressed ,as centipoise(cp).[1cp=0.001 pa.s].water at 20ºc has a viscocity of 1.0020cp.
OBSERVATION TABLE
RESULT = The percentage composition of unknown solution is 6.15%.
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