To Determine Surface Tension of Liquid by Drop Number Method

APPARATUS REQUIRED:

1. Water and given liquid

THEORY:

                 The formula for the calculation of surface tension of given liquid by drop number method using stalangometer is

 rl         =  nw×dl

rw                nl×dw

where rl and rw are the surface tension of the liquid and water respectively and dl and dw are the density of liquid and water respectively nl and nw are the number of drops made by same volume of liquid and water respectively.

Pyknometer is used to determine the density of liquid. Stalangometer is used to determine number of drops of liquid. If ml and mw are weights of given liquid and water then,

dl    =   ml/v    =   ml      [ i.e. weight of same volume is density ratio]

dw        mw/v       mw

PROCEDURE:

 A stalangometer was taken and rinsed with water. Then, it was filled with water taken from beaker. Any obstruction in the capillary tube of the stalangometer was checked carefully. The stalangometer was clamped vertically in a stand and water was allowed to fall drop wise through capillary tube. The reading from upper point to lower point was taken and total no. of drops was counted. The process was continued two or more times and total drops were counted. The same process was applied for given liquid and reading was noted.

OBSERVATION TABLE:

S.N.	Sample	No. of drops	Mean value
1.	water	30
	water	32	29
	water	27
2.	liquid	43
	liquid	40	41
	liquid	40

 Weight of empty pyknometer (w1) = 23.8057 g

Weight of pyknometer’s liquid (w2) = 34.0264 g

Weight of pyknometer’s water (w3) = 34.0647 g

Weight of given volume of liquid (m1) = w2 – w1

                                                               = 10.207 g

Weight of given volume of water (m2) = w3 – w1

                                                               = 10.259 g

Surface tension (rw) = 72.09 dyne/cm

CALCULATION:

here,

     Or, r1 =  nw (w3-w1   ) rw

          n1   w2 – w1                                 

= 28 (10.259   ) × 72.09

• 10.2207

= 0.707 × 1.003 × 72.09

= 51.111 dyne/cm      

RESULT:

            The surface tension of liquid by using stalangometer by dropwise method was found to be 51.111 dyne/cm.

CONCLUSION:

                            Hence, surface tension of liquid can be determined by drop wise method by using stalangometer.

PRECAUTION:

1. Reading should be noted carefully.
2. Chemical should be used carefully.
3. Apparatus should be handled carefully.
4. Any obstruction in capillary tube should be checked properly.