How to Determine the Parachor value of the given liquid?

 

Experiment:

Determine the Parachor value of the given liquid. Molecular weight of the given liquid is 32.


 

Theory:

 

Macleod in 1923 discovered a relationship between surface tension and density for normal liquids. It is expressed as

 

C = g1/4 / D – d

 

Where g is the surface tension of the liquid, D is density of the liquid, d is the density of vapour and C is a constant, characteristic of the liquid. This equation holds well over a wide range of temperature. In 1924, it was pointed out by Sudgen that the following expression is also valid.

MC = Mg1/4 / D – d

 

Where M is the molar mass (molecular weight). MC was called Parachor, denoted by [P].

 

Mg1/4 / D – d = [P]

 

At ordinary temperature d is negligible, therefore

[P] = Mg1/4/D

 

Apparatus:

Stalagmometer, specific gravity bottle, screw type pinch cock, beakers, rubber tube, balance, stand etc.

 

Procedure:

 

·         Take a stalagmometer, wash it with ether, dry it and then fill it with water up to the level of the upper mark A by sucking through rubber tube.

·         Release water at a very slow rate and count the number of drops of water from the upper mark A to the lower mark B.

·         Also count the number of drops for each of the given liquids in the same way.

·         Take a specific gravity bottle and weigh it. Then fill it with water and weight it.

·         Find the weight of water by subtracting the weight of empty bottle from the total weight of bottle filled with water.

·         Also find the weight of each liquid in the same way. Then calculate the density of each of the liquid as follows.

 

Density of Liquid = (Weight of liquid / Weight of water) x Density of water as density of water is usually taken as 1 therefore Density of liquid = (Weight of liquid / Weight of water)

 

Observations:

 

Liquid

No. of Drops (n)

Surface tension (g)

Water

 

 

Given Liquid

 

 

 

Room temperature =   oC

Weight of empty specific gravity bottle =W1 g

Weight of empty specific gravity bottle + water = W2 g

Weight of water = W2 – W1 = W3

Weight of specific gravity bottle + liquid 1 = W4 g

Weight of liquid =W4 – W1 = W5 g

 

Calculations:

 

Surface tension of a liquid is calculated using the following relationship

gl = gwx (nw / nl) x (dl/ dw)

 

Surface tension of water at 30oC is 71.22

Molar mass of the liquid =

 

 

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