Interfacial tension between water and organic Liquid heavier than water by Capillary Rise Method.

Ulhas Balkrishna Hadkar¹, Asavari Sameer Hadkar²

¹Director/Professor, Mumbai Educational Trust Institute of Pharmacy, Bandra (west), Mumbai – 400050.

²Research Assistant, Mumbai Educational Trust Institute of Pharmacy, Bandra (west), Mumbai – 400050.

*Corresponding Author E-mail: ulhashadkar@yahoo.com, asavarihadkar@gmail.com

ABSTRACT:

Interfacial tension between two liquids water and immiscible organic liquid heavier than water has been determined by capillary rise method. The difficulties encountered in the determination of interfacial tension by capillary rise method and how to overcome the difficulties has been discussed. The interfacial tensions between water and organic liquids, carbon tetrachloride, chloroform, nitrobenzene and o-anisidine which are heavier than water have been determined at room temperature (29±1^oC) by capillary rise method using a pyrex glass capillary tube of uniform radius. The values of the interfacial tension determined by the capillary rise method were found to be negative indicating that the interfacial tension was acting in the downward direction. The force in the vertically upward direction was considered as positive. The interfacial tensions determined by capillary rise method were in close agreement with the reported values.

KEYWORDS: Surface tension, Interfacial tension, temperature dependence, Capillary rise method, uniform radius, Drop weight method, Organic liquids.

INTRODUCTION:

Interfacial tension is the force per unit length existing at the interface between two immiscible liquid phases¹. Surface tension of a liquid is defined as the force in dynes acting along the surface of the liquid at right angle to any line in the surface one centimeter in length². The various methods used to determine interfacial tension between two immiscible liquids are Dunoy ring method, Drop weight method, Pendant drop method and Wilhelmy plate method. The interfacial tension between water and organic liquids lighter than water by capillary rise method have been reported by U.B. Hadkar³ et al.

The measurement of interfacial tension between immiscible liquids of equal density using a glass capillary tube has been reported by S.B. Reddy Karri and K. Mathur⁴. Interfacial tension measurement of immiscible liquids using a capillary tube has been reported by N. Rashidnia, R. Balasubsramaniam and D. Del Signore⁵. In the present investigation a capillary of uniform radius was used to determine the interfacial tension between water and the organic liquid heavier than water, namely, carbon tetrachloride, chloroform, nitrobenzene and o-anisidine.

MATERIAL AND METHODS:

Materials:

Organic liquids: carbon tetrachloride, chloroform, nitrobenzene and o-anisidine were of LR grade supplied by s-d Fine Chem-limited.

Capillary: Pyrex glass capillary of uniform bore size, radius 0.0165cm.

METHOD:

The capillary required for the experiment was prepared in the laboratory using a pyrex glass tube by heating it in a strong gas flame and pulling it sideways.

Uniformity of the bore size (radius) of the capillary:

The major difficulty in the capillary rise method was to confirm the uniformity of the bore size (radius) of the capillary. A simple method was used to confirm the uniformity of the radius of the capillary. The dry and clean capillary was held in a vertical position. A test tube filled with liquid toluene was raised upward slowly just to touch the toluene surface to the capillary tip. The test tube was slowly raised vertically upward and again slowly brought down so that the tip of the capillary was about 1mm inside the liquid toluene. The height of the steady toluene column was measured with an accuracy of ±0.05cm using a ruler graduated in mm. The procedure was repeated five times and the constant column height (h_o) of the liquid column was recorded. The test tube was then further raised so that the tip of the capillary was 1cm below the toluene surface. The constant height (h₁) of the toluene column in the capillary above the toluene surface was measured. The test tube was further raised slowly so that the tip of the capillary was 2, 3, 4, 5cm below the surface of toluene and the corresponding heights h₂, h₃, h₄, h₅ were measured. It was found that the height of the liquid column (h) above the liquid surface remained constant. This observation indicated that the capillary was of uniform bore size (uniform radius).

Determination of radius of the capillary:

The radius of the capillary was determined by using capillary rise method⁶. The tip of the capillary was dipped into the liquids of known surface tension namely chloroform, carbon tetrachloride, nitrobenzene. The equation used for the calculation of radius “r” is

2πrγcosθ   ₌ πr²hρg 

where,

r = radius of the capillary in cm

θ = angle of contact between liquid and glass which was considered as 0^o

γ = surface tension of the liquid in dynes/cm

h = height of the liquid column in the capillary in cm

ρ = density of the liquid in gm/cc

g = acceleration due to gravity in cm/s²

The average value of radius of the capillary determined by using the three liquids was 0.0165cm.

Interfacial Tension using Capillary Rise Method:

The capillary was cleaned with acetone and then with absolute alcohol and was dried. A test tube filled with distilled water was raised slowly till the water surface just touched the tip of the capillary tube, held in a vertical position. The water level in the capillary increased and remained steady. The steady height of the water column was found to be 9.0cm. The test tube was gradually lowered till the tip of the capillary was detached from the liquid surface. The test tube filled with organic liquid carbon tetrachloride (heavier than water) was gradually raised to touch the tip of the capillary containing the water column of height 9.0cm. It was observed that carbon tetrachloride did not enter the capillary even after raising the test tube by 1cm to 3cm. On lowering the test tube back to its original position, carbon tetrachloride level was found to remain at the tip of the capillary. It did not rise in the capillary. This was also observed with other organic liquids chloroform, nitrobenzene and o-anisidine. From this observation it was concluded that the interfacial tension between water and organic liquids heavier than water was acting in the downward direction.

The capillary was cleaned and dried, water was allowed to rise in the capillary (9.0cm).To reduce the weight of the water column in the capillary, the water level in the capillary was brought down to about 2cm to 4cm (h_w) by gently touching the tip of the capillary with a filter paper. The test tube filled with carbon tetrachloride was raised just to touch the tip of the capillary. It was observed that the carbon tetrachloride entered into the capillary (Fig 1). The test tube was gradually raised by a distance of about 3cm and brought back gradually till the carbon tetrachloride liquid surface just touched the tip of the capillary. The steady heights of the water column (h_w) and carbon tetrachloride column (h_o) were noted. The length of the liquid column was measured with the accuracy of ±0.05cm using a ruler graduated in mm. The experiment was repeated with other organic liquids heavier than water namely, chloroform, nitrobenzene and o-anisidine. The observations are recorded in Table 1.

Fig 1: Capillary Rise Method to determine interfacial tension.

h_w = Height of the water column

h_o = Height of the organic liquid column heavier than water

Calculation for the interfacial tension (γ_int) between water and Organic liquid heavier than water:

At equilibrium, force due to the surface tension of water and that due to the interfacial tension in the upward direction is balanced by the downward force namely, the weight of the water column and the weight of organic liquid column.

2πrγ_w cosθ_w   + 2πrγ_int cosθ_o/w   = m_wg + m_og

2πrγ_w cosθ_w   + 2πrγ_int cosθ_o/w   = πr²h_wρ_wg + πr²h_oρ_og   (1)

where,

m_w = mass of water column in gm

m_o = mass of organic liquid column in gm

g = acceleration due to gravity = 980 cm/s²

r = radius of the capillary in cm = 0.0165cm

γ_int = interfacial tension between water and organic liquid in dynes/cm

γ_w = the surface tension of water in dynes/cm = 72 dynes/cm

h_w = height of the water column in cm

ρ_w = density of water = 1.0 gm/cc

h₀ = height of the organic liquid column in cm

ρ_o = density of organic liquid in gm/cc

θ_w = angle of contact between water and glass

θ_o/w = angle of contact between interface of the two liquids and the capillary wall (glass)

The angle of contact θ_w and cos θ_o/w were considered as 0^o hence, cosθ_w = 1 and cosθ_o/w = 1

And substituting these values in equation (1),

∴ 2πrγ_w + 2πrγ_int = πr²h_wρ_wg + πr²h_oρ_og

2πr (γ_w + γ_int) = πr²g (h_w ρ_w + h_o ρ_o)

∴    -                          (2)

The values of interfacial tension determined at 29±1^oC are given in Table 1.

Table 1: Interfacial tension between water and organic liquids heavier than water at 29^oC

Sr. No	Organic liquids	Density gm/cc	Height of water column (hw) cm	Height of organic liquid column (ho) cm	Interfacial Tension (γint) dynes/cm by Capillary rise method at 29±1^oC	Standard deviation	Interfacial tension dynes/ cm (literature values) by Drop weight method
1	CCl4	1.583	3.1	0.35	42.46	±0.318	45^7 at 20^oC
2	CHCl3	1.498	3.5	1.3	27.94	±0.363	32.8^7 at 20^oC
3	nitrobenzene	1.200	2.7	2.8	23.01	±0.357	25^7 at 20^oC
4	o-anisidine	1.0864	3.6	3.0	16.58	±0.383	10.97*

The interfacial tension between o-anisidine and water has not been reported.

Freshly distilled o-anisidine was used since it deepens in colour on exposure to atmosphere.

In general, the surface tension of liquid decreases with increase in temperature. The dependence of surface tension on the temperature is given by the equation⁸

γ = α – bt                                                                       (3)

where, α is surface tension of the liquid in dynes/cm at a given temperature (20^oC) and t is the temperature in degree celsius and b is the constant for thr organic liquid given in the table of Lange’s Hand book of Chemistry. Assuming that equation (3) is also applicable to interfacial tension, equation (3) can be written as

γ_int^t = γ_{int 20}^o – bt 

γ_{int 29}^o = γ_{int 20}^o – b (29)                                                   (4)

Equation (4) gives variation of interfacial tension with temperature.

The interfacial tension between CCl₄/water, CHCl₃/water, nitrobenzene/water at 20^oC was calculated using equation (4) replacing the value of α by interfacial tension γ_int.

The literature value of interfacial tension reported in Table (1) was considered as α and the values of b, for CCl₄, CHCl₃, nitrobenzene were taken from Lange’s Handbook of chemistry and the value of t was taken as 29^oC.

The values of interfacial tension determined at 29^oC by capillary rise method were in the close agreement with the reported literature values as seen from Table 2.

Table 2: Comparison between Interfacial tension (literature values and the experimental values at 29^oC)

Sr. No	Organic liquids	γint20^o	b*	γint29^o	γexpt at 29±1^oC
1	CCl4	45	0.1224	41.45	42.46
2	CHCl3	32.8	0.1295	29.04	27.94
3	nitrobenzene	25	0.1157	21.65	23.01
4	o-anisidine	#			16.58

γ_{int 20}^o = Reported literature value of interfacial tension at 20^oC

b* = Value from Lange’s Handbook of Chemistry⁹

γ_{int 29}^o = Calculated literature value of interfacial tension at 29^oC using equation (4)

# = The interfacial tension has not been reported

γ_expt = Interfacial tension between water and organic liquid heavier than water at 29^oC determined by capillary rise method

RESULTS AND DISCUSSION:

The interfacial tension between water and organic liquids heavier than water has been reported by N. Rashinia¹⁰ et al by capillary rise method. How ever the authors have not given the observation details such as height of water column, height of organic liquid column. The values of interfacial tension reported are positive. The values of interfacial tension between water and organic liquids heavier than water were found to be negative by the authors of the present article. The negative sign indicates that the interfacial tension acts in the downward direction and that is the reason why the heavier liquid in the test tube did not rise in the capillary containing water of height 9.0cm. Hence the water column height in the capillary was reduced to 2-4cm. This decreased the weight of the water column in the capillary. The organic liquid was found to rise in the capillary after reducing the water column height, because the upward force due to surface tension of water then was greater than the interfacial tension between water and the organic liquid acting in the downward direction. The height of the water column h_w, the height of the organic liquid column h_o were recorded and used for the calculation of interfacial tension (γ_int) using equation (2). For the calculation of interfacial tension, angle of contact θ_w, θ_o/w were considered as 0^o. It has been reported¹¹ that if the angle of contact θ is less than 10^o the error in assuming it to be zero in equation (1) is less than 1.5%. The values of interfacial tension are reported in Table 1 neglecting the negative sign. The comparison between interfacial tension determined experimentally at 29±1^oC and the literature values at 29±1^oC are given in Table 2 and are in close agreement.

CONCLUSION:

The capillary rise method was successfully used to determine the interfacial tension between water and organic liquids heavier than water namely, carbon tetrachloride, chloroform, nitrobenzene and o-anisidine.

ACKNOWLEDGEMENT:

The authors of the article wish to thank the Trustees of Mumbai Educational Trust for the laboratory facilities provided to carry out the research work.

REFERENCES:

1. Martin’s Physical Pharmacy and Pharmaceutical Sciences. 2006. 5^th Ed, pp. 438.

2. A. Bahl, B. Bahl G. Tuli. Essentials of Physical Chemistry, S. Chand and Company Ltd. 2009, pp.423.

3. Ulhas Balkrishna Hadkar and Asavari Sameer Hadkar. Interfacial tension between water and organic liquid lighter than water by capillary rise method. Asian Journal of Pharmacy and Technology. Vol. 9, Issue 1, January- March 2019; pp 27-30.

4. S.B. Reddy Karri, V. K. Mathur. Measurement of Interfacial Tension of Immiscible Liquids of Equal Density. American Institute of Chemical Engineers Journal, Vol 34, Issue 1 January 1988; pp.155-157.     

5. N. Rashidnia, R. Balasubramaniam, D. Del Signore. Interfacial tension measurement of immiscible liquids using a capillary tube. Scientific and Technical Aerospace Report. March 1992.

6. Martin’s Physical Pharmacy and Pharmaceutical Sciences. 2005. 4^th Ed, pp. 336.

7. Leon Lachman, Herbert A Lieberman, Joseph. L. Kanig. The Theory and Practice of Industrial Pharmacy, 3^rd Ed, 1987. pp. 103.

8. Lange’s Handbook of Chemistry, Editor: John A. Dean, McGraw Hill Book Company, 12^th Ed. pp.10-98.

9. Lange’s Handbook of Chemistry, Editor: John A. Dean, McGraw Hill Book Company, 12^th Ed. pp.10-105, 10-112

10. Ibid 5

11. Ibid5

Received on 08.01.2020 Modified on 10.02.2020

Accepted on 24.02.2020      ©Asian Pharma Press All Right Reserved

Asian J. Pharm. Tech.  2020; 10(1):11-14.

DOI: 10.5958/2231-5713.2020.00003.3