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Detergents and Surface Tension

Last updated date: 28th May 2024
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An Introduction

There are some questions that we must have come across in our day-to-day lives. Have you ever encountered a raindrop that does not adhere to any glass panel in a uniform order? What is the speciality of detergent or soap that can wash our clothes much better than normal water? Well, in this subject, we are going to study and analyse all kinds of behaviours regarding surface tension and detergents.


What is Surface Tension? 

All the substances that we find in our surroundings consist of molecules which in turn are formed by the combination of one or more atoms. The substances are usually found in three states such as solid-liquid and gas. solution rigid bodies that do not change their shape and size. This is because the molecules of a solid are bound to each other by strong chemical forces. The chemical bonds between the molecules in liquids are relatively weaker and they can move around each other. all the molecules in the gaseous state are free to move randomly with respect to each other.

Thus surface tension is defined as the attractive force which is applied to the molecules available on the surface of the liquid by the molecules underneath. This inclines to attract into the bulk of the liquid and influences the liquid to imagine the shape consisting of the lowest surface area. Another special characteristic of the molecules in a liquid is their interaction with other molecules nearby them. They can be attracted to the molecules of subsistence which is known as cohesion or can be attracted more strongly to the molecules of other substances which is known as adhesion. If you observe a drop of water you can notice the cohesive force acting strongly to keep it in a round shape. This force of attraction applied by the molecules on the surface is known as surface tension.


Surface Tension of Soap Solution

Soap molecules consist of a long chain of hydrogen and carbon atoms. This is the infrastructure of atoms that enjoy inside water. The other terminal is easily connected with the soap molecule. The molecules of soap surround the water particle. The surface tension of water breaks with the help of the detergent molecules attached to the water molecule at both its ends.


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The grease particle is moved apart and connected with soap molecules, to be accomplished by a water jet spray. The two terminals of detergent molecules help to break the surface tension of water. This is called hydrophobic. The hydrophobic terminals of the detergent particle are being pushed up to the water surface in an attempt to draw out from the water molecule. This phenomenon helps to weaken the hydrogen bonding of water molecules available at the surface. This destroys the surface tension of water. The soap molecule does not desire to convert into liquid form in a soap and water solution. The molecules which have found their path to the surface destroy their path between the molecules of surface water by raising the hydrophobic ends on the water surface. This phenomenon breaks the water molecules apart from each other.



The long chain of hydrocarbons having sodium (Na) or potassium (K) atoms at one end are known to be a special type of sodium salts or potassium salts respectively. The Hydrocarbon part is usually the nonpolar portion that is hydrophobic in nature. and sodium or potassium atoms attached at one end are polar and hydrophilic in nature. The combination of two such distinct characteristics gives a unique property to the molecules of detergents. As when detergents mix with water it decreases the surface tension of water molecules so they are known as surfactants. When a hydrophobic substance such as oil or grease come in contact with detergent molecules then the nonpolar end gas is attached to the grease or oil molecule. This explains why grease or oil molecules get dissolved and removed in detergent or soap water instead of in pure water.

The effect of detergent on surface tension brings a non-adhesive nature to water molecules. It does not stick to the surface of the glass. It happens because of the cohesive force in the water-detergent molecule. The exact thing appears when it comes to washing clothes with water. Water can’t help much to clean the dirt. This is where we need detergent powder. The mixture of detergent and water decreases water’s surface tension. We call detergents and shops surfactants. The surfactants decrease the surface tension and increase the sticking capacity of the things. Water in combination with detergent has the capability of strain through thin fibres of dirty clothes. The detergent solution spreads throughout clothes more easily than water. This is the only reason why water can’t help along with the washing of clothes.


The Surface Tension of Water on Adding Detergent to It.

When detergent is combined with water, it reduces its surface tension. The compounds which help to reduce water’s surface tension are known as surfactants. In this whole phenomenon, the lowered surface tension area can be seen where the surfactant is combined with water. These surfactants can be illustrated as detergents, soaps, emulsifiers, foaming agents, and dispersants. The word “surfactant” is the composite of a surface-active agent.


How Detergent Reduces the Surface Tension of Water?

As we have seen how detergent is acting in the water molecule, we can easily determine that it lowers the surface tension in the water. This phenomenon is caused because of surfactants that reduce the surface tension.

What are the Factors Affecting Surface Tension?

These are the following reasons affecting surface tension


Surfactant- It is the prime factor that helps to reduce surface tension. The surfactants combine with a water molecule and lower its original surface tension.


Chemical additions- It changes the characteristics of surface tension. When some random chemical is mixed with a substance, it changes the surface tension. A surfactant in water is the best example of chemical addition.


Oxidation- It has a direct effect on surface tension. Oxidation is a natural phenomenon that appears when oxygen available in the atmosphere helps to lower the surface tension. The impurities that exist on the surface directly influence the surface tension.


Temperature- This temperature factor initiates a decrease in surface tension. Though surface tension decreases, the molecules inside the solution have become operative, with the hike of temperature turning into zero.


Uses of Surface Tension in Real Life

Some real-life applications of the surface tension are:

  • It generates a high surface tension in water. The molecules are combined to create a film on the water surface.

  • This film, or the thin layer, is strong enough to embrace light objects like a blade or a pin made of tin.

  • Surface tension helps to form water drops without making it into a thin layer.

  • It also permits water to pass through roots, stems, thermometers, and in the blood vessels of our body. The pulling effect comes into action when one molecule moves up; it attracts the nearest one.

FAQs on Detergents and Surface Tension

1. What are the different categories of detergents?

Depending on the charge of the surfactant group in a molecule of detergent they are known to be of 4 types. The first classification is among ionic detergents and non-ionic detergents. Non-ionic detergents don't have any charge on the hydrophilic head groups. The ionic detergent molecule with a charged particle can be an Anionic detergent or Cationic detergent. Anionic detergent is the most common one with a fatty acid group as alkylbenzene sulfonate.  In the cationic group, it is replaced by quaternary ammonium. The other type is amphoteric detergents. It also has a neutral charge due to the presence of two positive and negative charges in equal amounts.

2. What are the benefits of surface tension?

Surface tension is a very peculiar and important property of liquid or fluid molecules that we observe in our nature. The element Mercury (Hg) is a liquid metal and is known to have the highest surface tension. It is used in thermometers. Detergents are used while washing clothes to decrease their surface tension and make them more effective. The capillary action of water is also a property of water-related surface tension. Due to capillary action, the water at groundwater tables rises up through the small pores of soil particles and gets available to the plants growing on the surface.

3. How does the mixing of detergents in water change its quality?

The cleaning action performed by water is due to the property of surface tension of water containing dissolved water detergent. Due to less surface tension, it sticks easily to any surface nearby it and wets the cloth dipped inside it. The dirt in the cloth which is a hydrophobic oil or grease particle gets attached to the hydrophobic sodium ends of the detergent molecule. The other portion of the detergent molecule which is hydrophilic in nature gets attached to the water molecules. Thereby the detergent molecules remove the dirt clinging to the cloth.

4. Are there any chemical reaction formulas and equations to be remembered under this topic?

Though there are very few formulas for the different types of detergent that we use in our daily life, detergents are a very vast category in itself studied by organic chemistry researchers. For high school level chemistry, there are very few formulas to be remembered. Students can learn about all the types and formulas of detergents in the concerned chapter and also by the resources provided by Vedantu. The resource articles on all topics are available at completely free cost after registration on the portal.

5. What is the chemical formula of detergents or soaps?

The Chemical formula of any soap or detergent is a little complex. The long hydrocarbon portion is usually a chain of alkyl hydrogen sulphate or sometimes a long chain of benzene sulphonic acid. The word has been adopted from a Latin verb detergent that means clean by wiping or polishing. Some of the common formulas are Linear alkylbenzene sulphonates, sodium dodecylbenzene sulfonates. Some of the formulas of co-surfactants that we learn in this chapter are cocamidopropylamine oxide and the zwitterionic Cocamidopropyl betaine and many more.

6. Why is the surface tension of water lowered by soap?

Soap molecules contain long chains of hydrogen as well as carbon atoms that differentiate the water molecules from each other by decreasing their surface tension. As a result, there is a rise in the distance between water molecules.

7. What is the portrayal of detergent?

It helps to reduce the surface tension of water. Detergent acts as a surface-active agent or surfactant for short. They act with a water molecule to create a gap between them, which lowers the surface tension among them.

8. Mention some reaches, which helps to increase the surface tension of water?

The availability of impurities in the surface water reduces its surface tension. When the highly soluble impurities are added to water molecules, it pushes to the surface tension of water.

9. What happens when water will lose its surface tension?

If there is no surface tension, the water molecules will evaporate immediately. This is a condition which only arises when there will be no attractive forces among the molecules of the fluid.

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