Capillarity: Surface Tension and Liquid Surface

Topics: Surface tension, Liquid, Capillary action Pages: 23 (4798 words) Published: April 25, 2013
Determination of Cleansing Action of Detergents

(Using Capillary rise)


This project report explains about the surface tension and capillarity of liquid through a simple experiment of finding the capillarity of various detergents. Oil stains and grease on dirty clothes cannot be removed, using water alone, because water does not wet them. If detergents added , surface tension is decreased, the area of contact is increased. Detergent molecules have the shape of a hairpin, one of which is attracted to water and the other end to the molecule of the grease, thus forming a water grease interface and so the surface tension is reduced. The dirt can be removed and carried away by the flow of the water.


Two capillary tubes of different radii are cleaned well by immersing in caustic soda, dilute metric acid and distilled water. The liquid rises in the tubes due to the surface tension. The liquid meniscus is seen in one tube. The microscope reading is taken. The needle N is adjusted such that it just touches the liquid surface. The differences between the two readings give the height of the liquid raised in the tube.

The first chapter explains surface tension and capillarity by taking examples from day to day life and from a simple experiment .it gives the definition of surface tension. It also explains cohesive and adhesive force. Explanation of surface tension based on molecular theory is also given in this chapter. It gives the reason why the shape of small drops are spherical whereas larger drops are elliptical. This chapter also gives a brief description of angle between the tangent to the liquid surface at the point of contact and solid surface inside the liquid, which is called angle of contact. The chapter also informs about the pressure difference across a liquid surface and excess pressure inside a drop. All basics of surface tension are covered in this chapter.

The second chapter instructs us with the steps by which we can find the surface tension of water when different detergents are added into it.

The readings taken from the experiment can be observed in the third chapter. The surface tension of water on adding various detergents is also calculated in this chapter. The fourth chapter gives the complete analysis of the experiment done. The last chapter gives the sources of this report. Contents

Page No.

Chapter 1 : Introduction 4 1.1: Experiment to illustrate surface tension. 5 1.2: Shape of liquid meniscus in a tube. 9 1.3: Capillarity 12 1.4: Rise of liquid in a tube of insufficient length 13

Chapter 2 : Experiment to find the surface tension by capillary rise 14 method.
2.1: Measurement of surface tension by capillary rise method. 15

Chapter 3 : Observations of calculation. 16 3.1 : Least count of traveling microscope. 18 3.2 : To find mean height of capillary rise of each detergent. 18 3.3 : Calculation of surface tension of each detergent. 19

Chapter 4 : Result analysis 20 Chapter5 : Bibliography...
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