Determination of Surface tension of liquid sample by Drop weight method - Principle, Procedure, Calculation

Determination of surface tension of liquid sample by drop weight method

Aim

To determine the surface tension of a given liquid by drop weight method.

Requirement

Stalagmometer

100ml beaker

Liquid sample

Distilled water

Weighing balance

Principle

The surface tension is defined as force in dynes acting along the surface of the liquid at right angle to any line in 1 cm length. In CGS system the unit is dynes/cm (dynes cm^-1). In SI system the unit is newton/metre (Nm^-1).

The surface tension of a liquid can be determine by using stalogmometer by drop weight  method. The surface tension of a liquid sample is calculated by following formula.

γ₂= W₂/W₁  × γ₁

Where,

γ₂ = Surface tension  of a given liquid sample  in dynes/cm

γ₁ = Surface tension  of a given liquid water is 72.75 dynes/cm

W₂ = Weight  of drops of liquid sample

W₁ = Weight  of drops of water

 

The surface tension is determined by using stalagmometer. Surface tension of sample solution depends on the concentration of the solution.

Procedure

1. Take a clean stalagmometer and rinse with acetone then dry it in a hot air oven.

2. Fix the stalagmometer to the stand firmly in a  vertical position and dip the stalagmometer in a beaker of water and suck water upto the  upper mark.

3. 20 – 30 drops of water is collected from the stalagmometer into the specific gravity bottle and weight it.

4. Remove the water drops, clean the stalagmometer then repeat the procedure for weight  the drops of sample by following the above mentioned procedure surface tension of the given sample was calculated by using following formula.  

γ₂= W₂/W₁  × γ₁

Note :  Surface tension of water is 72.75 dynes/cm

 

Stalagmometer

Calculation

Room temperature = ---------- °C

Weight of empty specific gravity bottle                                        (A) = ------------g

Weight of  specific gravity bottle and ------drops of water           (B) = ------------g

Weight of specific gravity bottle and -----drops of liquid sample (C) = ------------g

Weight  of Water           (W1)  = B - A                       

                                                        =-------------------------

                                                       =------------------------- g

Weight of liquid sample (W2) = C - A

                                                       = -------------------------

                                                       = ------------------------- g

 

 

 Surface tension of liquid sample          (γ₂)= W₂/W₁  × γ₁

                                                                        = ------------------------------

                                                                        = ------------------------------

                                                                        = ------------------------------ dynes/cm

 

Report

The surface tension of the given liquid sample by drop count method was found to be  ----------------------- dynes/cm.