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LOVE YOU GUYS Determination of surface tension by drop weight method || Physical Pharmaceutics 1 || B.Pharmacy
Object: Determination of Surface Tension by drop weight method
Requirements: Stalagmometer, beaker, graph sheets, weighing bottle, balance
Theory:
Surface tension is defined as the force in dynes acting on the surface of the liquid at right angles to any line of length of surface 1 cm. the unit of surface tension is dyne/cm or Newton/meter.
Surface tension is observed in the liquid due to intermolecular forces of attraction. When substances are added to liquids, they alter the surface and interfacial tension. For example- electrolytes cause a slight increase, on the other hand certain molecules like surfactants decrease the surface and interfacial tension. Surface tension can be determined by capillary rise method, Du-Nouy tensiometer method, drop weight and drop count method with the help of a stalagmometer.
Procedure
A. Clean and dry the stalagmometer with H2O and then with acetone.
B. Suck water in stalagmometer and adjust equipment in such a way that number of drops coming out of is approximately 30 drops per minute.
C. Weigh an empty weighing bottle and note down the weight
D. Once the equipment is fixed, suck water and collect 20 drops of water into the weighing bottle
E. replace the water with the sample solution and follow the procedure as mentioned above for 2 times and find out the weight of one drop of water
Observations
Sl. No.
Sample
Weight of empty bottle (g)
Weight of bottle+ 20 drops of water (g)
Weight of 20 drops (g)
Weight of one drop (g)
Average weight of one drop (g)
Surface tension (dyne/cm)
1.
Water
1.
2.
2.
Sample
1.
2.
5. Calculations
Formula for determination of surface tension is given by
γ1 = (W1/W2) / γw
Where, γ1 is surface tension of the sample solution
W1 is weight of 01 drop of sample
W2 is weight of 01 drop of water
γw is surface tension of water
Results
Calculate the surface tension with the help of the given equation. The surface tension of the given sample was found to be ..........
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