To determine the viscosity of given unknown liquid.

 

Experiment

Aim:

To determine the viscosity of given unknown liquid.

Requirements:

• Oswald viscometer

• Relative density bottle 

• Stand 

• Unknown liquid

• Beaker 

• Distilled water

Theory:

Principle:

• The force of friction with the one part of the liquid offer to another part of liquid is 

called viscosity. For measuring the viscosity co-efficient Oswald viscometer is used 

which is basedon poise tuller’s law.

• According to this law the rate of flow of liquid through a capillary tube having viscosity 

co-efficient (n) can be expressed as

      N = 𝜋r 2tp/8vl

r → Radius of the capillary tube (cm).

n → Viscosity co-efficient (poise).

V → volume of liquid.

t→flow time in seconds through capillary 

l→Length of capillary

p→Hydrostatic pressure.

• Since the hydro pressure.(driving force)of the liquid is given by,

• P=dgh

P = dgh

h→ Height of the column.

d→ Density of the liquid.

             N α Pt

• If n, and n2 of the viscosity co-efficient of liquid D1 and D2 are the density of liquid as 

well as t1 and t2 are the time of flow of equal volume of liquid through the capillary respectively then 

n1 α d1 ght1

n2α d2 ght2

n1 /n2 = d1 ght1 / d2 ght2

n1 /n2 = d1 t1 / d2 t2

• Here, usually the viscosity of the given liquid is measured with respective water whose viscosity is known as very accurately at different temperature.

o The SI unit of viscosity of is pascal second.

• Pas = Kg m-1 s-1

• The cgs unit for the same is poise. It is most commonly expressed as centipoises (icp = 0.001 pascal sec).

• Water at 20 ̊ C has viscosity of 1.0020 cp.

Procedure: 

• Wash the relative density bottle with distilled water and dried. Take the weight of empty and 

filled relative density bottle with the given liquid clean and rinse the viscometer property with distilled water.

• Fix the viscometer vertically in the stand and fill the specific amount of given unknown liquid in viscometer.

• Time offlow where recorded when the liquid starts to flow from the mark C and D above and below the bulb A. the experiment is repeated 3-4 times.

Observation:

Draw a observation table.

Calculation:

Weight of an empty density bottle (w1) =

Weight of the density bottle with water (w2) =

Weight of the density bottle with unknown liquid (w3) =

Weight of the water ( ww) = w2 - w1

Weight of the liquid ( wL) = w3 - w1

Relative density = Demsity of liquid/Density of water

Densisty of liquid (d2 ) = mass/volume

Densisty of the water (d1) = masss /volume

Viscosity of liquid n2 = e2t2 / e1t1 X n1

Result:

The viscosity of the unknown liquid was found to be ______centipoises.