To determine the relative viscosity of given liquid using Ostwald’s viscometer

To determine the relative viscosity of given liquid using Ostwald’s viscometer
*Presentation Overview*
Aim, Apparatus and Chemicals, Theory, Procedure, Observations, Calculations, Result

1. To determine the relative viscosity of given liquid using Ostwald’s viscometer Dr. N. G. Telkapalliwar Associate Professor Department of Chemistry Dr. Ambedkar College, Nagpur 1

2. Presentation Overview Aim: To determine the relative viscosity of given liquid using Ostwald’s viscometer Aim Apparatus and Chemicals Theory Procedure Observations Calculations Result 2

3. Aim: To determine the relative viscosity of given liquid using Ostwald’s viscometer Theory Viscosity is the one of property of liquid. A liquid may be considered to be consisting of molecular layers arranged one over the other. When a shearing force is applied to a liquid, it flows. However, the forces of friction between the layers offer resistance to this flow. Viscosity of a liquid is a measure of its frictional resistance. Let us examine a liquid flowing on a glass surface. The molecular layer in contact with the stationary surface has zero velocity. The successive layers above it move with increasingly higher velocities in the direction of the flow. Now consider two adjacent moving layers of a liquid. Let these be separated by a distance dx and have a velocity difference dv . The force of friction (F) resisting the relative motion of the two layers is directly proportional to the area A and the velocity difference dv , while it is inversely proportional to the distance dx between the layers. 3

4. Aim: To determine the relative viscosity of given liquid using Ostwald’s viscometer That is, Where, η (Greek letter eta) is the proportionality constant. It is known as the Coefficient of Viscosity or simply viscosity of a liquid. η has a specific value for a given liquid at the same temperature. Coefficient of Viscosity is defined as the force of resistance per unit area which will maintain unit velocity difference between two layers of a liquid at a unit distance from each other. η = F When, A=1, dv =1, & dx =1 Units of Viscosity CGS unit of η is g cm –1 s –1 . It is called poise (P). SI unit is kg m –1 s –1 . One poise is equal to one-tenth of the SI unit i.e. 1 poise = 1 g cm –1 s –1 = 0.1 kg m –1 s –1 4

5. Aim: To determine the relative viscosity of given liquid using Ostwald’s viscometer Ostwald Viscometer There are intermolecular forces in liquid layers which are responsible for viscosity. Viscosity of a liquid can be determined on the basis of flow time. In fact, viscosity is directly proportional to the flow time. This principle has been used in Ostawald’s viscometer. It consist of two bulbs joined by a U-tube containing a capillary tube. 5

6. Aim: To determine the relative viscosity of given liquid using Ostwald’s viscometer Apparatus Required Beaker Ostwald’s viscometer Pipette Stop Watch The relative viscosity coefficient is calculated from the expression: Where, η 1 and η 2 are the viscosity coefficients of water and given liquid. t 1 and t 2 are the flow time of water and given liquid d 1 and d 2 are the densities of water and given liquid. Knowing the value of the viscosity coefficient of water (η 1 ) at the temperature of the experiment, the absolute viscosity coefficient (η 2 ) of the given liquid can be found. Formula Density bottle 6

7. Aim: To determine the relative viscosity of given liquid using Ostwald’s viscometer Procedure Part-I : Determination of densities of water and given liquid (ethanol) Clean the density bottle with chromic acid solution and then with distilled water. Rinse with water and ether and then dry. Weigh an empty density bottle (W 1 ). Fill the density bottle with distilled water completely, insert the stopper and weigh again (W 2 ). Take out the distilled water and rinse the density bottle 2-3 times with given experimental liquid (ethanol). Fill the given experimental liquid (ethanol) into the density bottle and record the weight again (W 3 ). 7

8. Aim: To determine the relative viscosity of given liquid using Ostwald’s viscometer Procedure Part-II : Determination of viscosity Clean the viscometer with chromic acid solution and then with distilled water. Rinse with water and ether and then dry. Attach the viscometer to the burette stand in exactly vertical position. Fill the distilled water in the lower bulb of the viscometer till the bulb fills completely. Suck the distilled water from other end through rubber tube above mark (A). Allow water to flow freely. Start the stopwatch as soon as the upper layer of water crosses mark A and stop the stopwatch as soon as it crosses mark (B). Repeat the recording of flow time three times for distilled water as well as for the given experimental liquid (ethanol). 8

9. Aim: To determine the relative viscosity of given liquid using Ostwald’s viscometer Observations and Calculations Part-I : Determination of densities of water and given liquid (ethanol) Room temperature = …………… O C Weight of empty density bottle= W 1 = …………. g. Weight of density bottle with water= W 2 = …………. g. Weight of density bottle with given liquid (ethanol) = W 3 = …………. g. Volume of density bottle =V= ………. ml 9

10. Aim: To determine the relative viscosity of given liquid using Ostwald’s viscometer Observations and Calculations Part-II : Determination relative viscosity and absolute viscosity of ethanol Sr. No. Flow Time (Sec) Relative Viscosity Absolute Viscosity For Water Mean (t 1 ) For Ethanol Mean (t 1 ) 1 -- -- -- -- 2 -- -- -- -- 3 -- -- Result: 1) R elative viscosity of given liquid (ethanol) relative to water was found to be ………. 2) Absolute viscosity of given liquid (ethanol) was found to be ………… Poise Viscosity of water at room temperature = η 1 = ……… Poise 10

11. References Essentials of Physical Chemistry, S. Chand Publication by Arun Bahl , B.S. Bahl , G. D. Tuli . University Chemistry, Volume I, Alliance & Co., by R. M. Jugade . A Text Book of Chemistry, B.sc. SEM- I, Himalaya Publishing House. The contents, materials, images, etc. used in this video/presentation are taken from open sources (Internet and Books) for educational purposes only and not meant for any commercial distribution. 11